solar_energy

Passive Solar Energy

Active solar heating systems involve installing special equipment that uses energy from the sun to heat or cool existing structures. Passive solar energy systems involve designing the structures themselves in ways that use solar energy for heating and cooling. For example, in this home, a ìsun spaceî serves as a collector in winter when the solar shades are open and as a cooler in summer when the solar shades are closed. Thick concrete walls modulate wide swings in temperature by absorbing heat in winter and insulating in summer. Water compartments provide a thermal mass for storing heat during the day and releasing heat at night.

© Microsoft Corporation. All Rights Reserved.¹

INTRODUCTION  ÝSolar Energy, radiant energy produced in the sun as a result of nuclear fusion reactions (see Nuclear Energy; Sun). It is transmitted to the earth through space in quanta of energy called photons (see Electromagnetic Radiation; Photon), which interact with the earthís atmosphere and surface. The strength of solar radiation at the outer edge of the earthís atmosphere when the earth is taken to be at its average distance from the sun is called the solar constant, the mean value of which is 1.37 × 10⁶ ergs per sec per cm², or about 2 calories per min per cm². The intensity is not constant, however; it appears to vary by about 0.2 percent in 30 years. The intensity of energy actually available at the earthís surface is less than the solar constant because of absorption and scattering of radiant energy as photons interact with the atmosphere.

The strength of the solar energy available at any point on the earth depends, in a complicated but predictable way, on the day of the year, the time of day, and the latitude of the collection point. Furthermore, the amount of solar energy that can be collected depends on the orientation of the collecting object.

        II      NATURAL TRANSFORMATION OF SOLAR ENERGY Ý
Natural collection of solar energy occurs in the earthís atmosphere, oceans, and plant life. Interactions between the sunís energy, the oceans, and the atmosphere, for example, produce the winds, which have been used for centuries to turn windmills. Modern applications of wind energy use strong, light, weather-resistant aerodynamically designed wind machines that, when attached to generators, produce electricity for local, specialized use or as part of a community or regional network of electric power distribution. See Windmill.

Approximately 30 percent of the solar energy reaching the outer edge of the atmosphere is consumed in the hydrologic cycle, which produces rainfall and the potential energy of water in mountain streams and rivers (see Potential Energy). The power produced by these flowing waters as they pass through modern turbines is called hydroelectric power. See also Dam; Meteorology; Water Supply and Waterworks.

Through the process of photosynthesis, solar energy contributes to the growth of plant life (biomass) that can be used as fuel, including wood and the fossil fuels that are derived from geologically ancient plant life. Fuels such as alcohol or methane can also be extracted from biomass.

The oceans also represent a form of natural collection of solar energy. As a result of the absorption of solar energy in the ocean and ocean currents, temperature gradients occur in the ocean. In some locations, these vertical variations approach 20ƒ C (36ƒ F) over a distance of a few hundred meters. When large masses exist at different temperatures, thermodynamic principles predict that a power-generating cycle can be created to remove energy from the high-temperature mass and transfer a lesser amount of energy to a low-temperature mass (see Thermodynamics). The difference in these two heat energies manifests itself as mechanical energy (for example, output from a turbine), which can be linked with a generator to produce electricity. Such systems, called ocean thermal energy conversion (OTEC) systems, require enormous heat exchangers and other hardware in the ocean to produce electricity in the megawatt range. See also Ocean and Oceanography.

        III     DIRECT COLLECTION OF SOLAR ENERGY Ý
The direct collection of solar energy involves artificial devices, called solar collectors, that are designed to collect the energy, sometimes through prior focusing of the sunís rays. The energy, once collected, is used in a thermal process or a photoelectric, or photovoltaic, process. In thermal processes, solar energy is used to heat a gas or liquid, which is then stored or distributed. In the photovoltaic process, solar energy is converted directly to electrical energy without intermediate mechanical devices (see Photoelectric Effect). Solar collectors are of two fundamental types: flat plate collectors and concentrating collectors.

        A       Flat Plate Collectors Ý
In thermal processes, flat plate collectors intercept solar radiation on an absorber plate in which passages for so-called carrier fluid are integral or to which they are attached. The carrier fluid (liquid or air) passing through these flow channels has its temperature increased by heat transfer from the absorber plate (see Heat; Heat Transfer). The energy transferred to the carrier fluid, when divided by the solar energy incident on the collector and expressed as a percentage, is called the instantaneous collector efficiency. Flat plate collectors generally have one or more optically transparent cover plates intended to minimize heat losses from the absorber plate, in an effort to achieve maximum efficiency. Typically, they are capable of heating carrier fluids up to 82ƒ C (180ƒ F) with efficiencies between 40 and 80 percent.

Flat plate collectors have been used efficiently for water and comfort heating. Typical residential applications employ roof-mounted, fixed collectors. In the northern hemisphere, they are oriented in a southerly direction; in the southern hemisphere, they are oriented to face north. The optimum angle at which to mount collectors relative to the horizontal plane depends on the latitude of the installation. Generally, for year-round applications such as providing hot water, collectors are tilted (relative to the horizontal plane) at an angle equal to the latitude angle ± 15ƒ, and are oriented to face true south (or north) within ± 20ƒ.

In addition to the flat plate collectors, typical hot-water and comfort heating systems include circulating pumps, temperature sensors, automatic controllers to activate the circulating pump, and a storage device. Either air or a liquid (water or a water-antifreeze mixture) can be used as the fluid in the solar heating system, and a rock bed or a well-insulated water storage tank typically serves as an energy storage medium.

        B       Concentrating Collectors Ý
For applications such as air conditioning, central power generation, and numerous industrial heat requirements, flat plate collectors generally cannot provide carrier fluids at temperatures sufficiently elevated to be effective. They may be used as first-stage heat input devices; the temperature of the carrier fluid is then boosted by other conventional heating means. Alternatively, more complex and expensive concentrating collectors can be used. These are devices that optically reflect and focus incident solar energy onto a small receiving area. As a result of this concentration, the intensity of the solar energy is magnified, and the temperatures that can be achieved at the receiver (called the ìtargetî) can approach several hundred or even several thousand degrees Celsius. The concentrators must move to track the sun if they are to perform effectively, and the devices used to achieve this are called heliostats.

        C       Solar Furnaces Ý
One important high-temperature application of concentrators is for solar furnaces. The largest of these, located at Odeillo in the Pyrenees Mountains of France, uses 9600 reflectors with a total area of approximately 1860 sq m (about 20,000 sq ft) to produce temperatures as high as 4000ƒ C (7200ƒ F). Such furnaces are ideal for research requiring high temperatures and contaminant-free environmentsófor example, materials research.

        D       Central Receivers Ý
Central electric power generation from solar energy is under development. In the central receiver, or ìpower tower,î concept, an array of reflectors mounted on computer-controlled heliostats reflect and focus the sunís rays onto a water boiler mounted on a tower. The steam thus generated can be used in a conventional power-plant cycle to produce electricity.

        E       Solar Cooling ÝSolar cooling can be achieved through the use of solar energy as a heat source in an absorption cooling cycle (see Refrigeration). One component of standard absorption cooling systems, called the generator, requires a heat source. Because temperatures in excess of 150ƒ C (300ƒ F) are generally required for the absorption device to perform effectively, concentrating collectors are more suitable than flat plate collectors for cooling applications.

        IV      PHOTOVOLTAICS Ý
Solar cells made from thin slices of crystalline silicon, gallium arsenide, or other semiconductor materials convert solar radiation directly into electricity. Cells with conversion efficiencies in excess of 30 percent are now available. By connecting large numbers of these cells into modules, the cost of photovoltaic electricity has been reduced to 30 cents per kwh, about twice the rate that the largest U.S. cities were paying for electricity in 1989. Current use of solar cells is limited to remote, unattended low-power devices such as buoys and equipment aboard spacecraft.

        V       SOLAR ENERGY FROM SPACE ÝA futuristic scheme that has been proposed to produce power on a large scale envisions placing giant solar modules in geosynchronous earth orbit, where energy generated from sunlight would be converted to microwaves and beamed to antennas on earth for reconversion to electric power. To produce as much power as five large nuclear power plants (1 billion watts each) several square miles of solar collectors, weighing 10 million pounds, would have to be assembled in orbit; an earth-based antenna 5 miles in diameter would be required. Smaller systems could be built for remote islands, but the economy of scale suggests advantages to a single large system (see Space Exploration).

        VI      SOLAR ENERGY STORAGE DEVICES Ý
Because of the intermittent nature of solar radiation as an energy source, excess solar energy during periods of small demand must be stored in order to meet demands when solar energy availability is insufficient. Besides simple water and rock storage systems, more compact devices that rely on the phase-change characteristics of eutectic salts (salts that melt at low temperatures) can also be used, particularly in cooling applications. Batteries can serve as storage devices for excess electric energy produced from wind or photovoltaic devices (see Battery). A broader concept is the delivery of excess electric energy to existing power networks and the use of these power networks as supplemental sources when solar availability is insufficient. The economics and reliability of such a scheme, however, place limits on this alternative.

Contributed By:
Richard S. Thorsen
²

Solar Home

In this solar home in Corrales, New Mexico, a flat plate solar collector (lower right) provides energy to heat water pumped by the windmill. The water is stored in large drums on the side of the home.

Tom McHugh/Photo Researchers, Inc.³

Solar Collecting Panels

Panels on a rooftop collect energy from sunlight and convert it directly into electricity. The solar panels contain semiconducting materials. When light strikes the material, electrons move from one layer of the material to another, forming an electric current.

Chinch Gryniewicz/Corbis⁴

Solar Heating

Flate plate collectors utilize the sunís energy to warm a carrier fluid, which in turn provides usable heat to a household. The carrier fluid, which in this case is water, flows through copper tubing in the solar collector, and in the process absorbs some of the sunís energy. Next, the carrier fluid moves to the heat exchange, where the carrier fluid warms water that is used by the household. Finally, a pump moves the carrier fluid back to the solar collector to repeat the cycle.

© Microsoft Corporation. All Rights Reserved.⁵

Photovoltaic Cells

In a photovoltaic cell, light excites electrons to move from one layer to another through semi-conductive silicon materials. This produces an electric current.

Walter Rawlings/Robert Harding Picture Library⁶

Solar Energy

Photovoltaic cells are a means of directly converting radiation from the sun into electricity. These cells, made from thin slices of semiconductor materials, appear to produce significant amounts of energy at little cost. Experiments with photovoltaics continue in Arizonaís desert areas.

Arizona Solar Energy Office⁷

Solar Maximum Mission

The Solar Maximum Mission Satellite was a scientific satellite designed to study solar radiation. Launched in early 1980, the craft failed later in the year. It was repaired and relaunched by the space shuttle in 1984, collecting information until 1989, when it was destroyed by a solar flare. Information collected by the satellite indicated that the sunís corona experiences an unexpectedly high amount of violent activity related to sunspot cycling. Data also showed that sunspots reduce the amount of solar energy reaching the earthís atmosphere.

NASA⁸

The Energy Story

Introduction

Energy is one of the most fundamental parts of our universe.

We use energy to do work. Energy lights our cities. Energy powers our vehicles, trains, planes and rockets. Energy warms our homes, cooks our food, plays our music, gives us pictures on television. Energy powers machinery in factories.

Energy is defined as "the ability to do work."

When we eat, our bodies transform the food into energy to do work. When we run or walk,
we "burn" food energy in our bodies. When we think or read or write, we are also doing work.

Cars, planes, trollies, boats and machinery also transform energy into work.

Work means moving something, lifting something, warming something, lighting something. All these are a few of the various types of work. But where does energy come from?

There are many sources of energy. In this guide, we will be looking at the energy that makes our world work. Energy is an important part of our daily lives.

The forms of energy we will look at include:

• Geothermal Energy
• Fossil Fuels -- Coal, Oil and Natural Gas
• Hydro Power and Ocean Energy
• Nuclear Energy
• Solar Energy
• Wind Energy

We will also look at turbines and generators, at what electricity is, how energy is sent to users, and how we can decrease the energy we use.

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Table of Contents

Chapter 1: Energy -- What Is It?

Chapter 2: What is Electricity?

Chapter 3: Generators, Turbines and Power Plants

Chapter 4: Geothermal Energy

Chapter 5: Fossil Fuels -- Coal, Oil and Natural Gas

Chapter 6: Hydro Power

Chapter 7: Nuclear Energy -- Fission and Fusion

Chapter 8: Ocean Energy

Chapter 9: Solar Energy

Chapter 10: Wind Energy

Chapter 11: Electricity Transmission System

Chapter 12: Natural Gas Distribution System

Chapter 13: Energy for Transportation

Chapter 14: Biomass Energy

Chapter 15: Saving Energy and Energy Efficiency

Conclusion

All around us energy is causing things to happen. Look out a window. If it's daytime, the sun is giving out light and heat energy. If it's nighttime, street lamps are using electrical energy to make light.

A car drives by your school or house. It is being powered by gasoline, a type of stored energy.

Our bodies eat food, which has energy in it. We use that food to play or study.

Energy makes everything happen. Energy can be divided into two different types, depending on whether the energy is moving or stored.

Energy that is stored is called potential energy.

Energy that is moving is called kinetic energy.

If you have a pencil on your desk, try this example that shows the two different types of energy.

Put the pencil at the side of the desk and push it off to the floor. The pencil is moving and is using kinetic energy.

Now, pick the pencil back up and put it back on the desk. You used your own energy to lift and move the pencil. Moving it higher than the floor adds energy to it. As it rests on the desk, it has potential energy. The higher it is, the further it could fall, so the pencil has more potential energy the higher you raise it.

If you have a rubber band, stretch it out. The stretched rubber band has potential energy. If you let it go, it moves and has kinetic energy. Just don't shoot anyone with the rubber band!

Energy is measured in a couple of different ways.

One of the basic measuring blocks is called a Btu. This stands for British thermal unit.

Btu is defined as the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.

One Btu equals about:

• One blue-tip kitchen match

One-thousand (1,000) Btu roughly equals:

• One average candy bar
• 4/5 of a peanut butter and jelly sandwich

It takes, for example, about 2,000 Btus to make a pot of coffee.

Energy can also be measured in joules. Joules sounds the same way as the word jewels, like diamonds and emeralds. It takes 1,000 joules to equal a British thermal unit. So:

	 1,000 joules = 1 Btu

So, it would take 2 million joules to make a pot of coffee.

Joule is named after an English physicist named James Prescott Joule (pictured on the left) who lived from 1818 to 1889. He discovered that heat is a type of energy.

One joule is the amount of energy needed to lift one pound about nine inches.

Around the world, scientists measure energy in joules rather than Btus. It's much like people around the world using the metric system, meters and kilograms, instead of the English system of feet and pounds.

Like in the metric system, you can have kilojoules -- "kilo" means 1,000.

	1,000 joules = 1 kilojoule = 1 Btu

A piece of buttered toast contains about 315 kilojoules of energy. With that energy you could:

• Jog for 6 minutes
• Bicycle for 10 minutes
• Walk briskly for 15 minutes
• Sleep for 1-1/2 hours
• Run a car for 7 seconds at 80 kilometers per hour (about 50 miles per hour)
• Light a 60 watt light bulb for 1-1/2 hours

Energy can only be changed into another sort of energy. It cannot be created nor can it be destroyed.

Here are some changes in energy from one form to another.

Stored energy in a flashlight's batteries becomes light energy when turned on.

Food contains energy stored as chemical potential energy. Your body uses the stored energy to do work, kinetic energy.

If you overeat, the food's energy is stored as potential energy in fat.

When you talk on the phone, your voice is changed to electrical energy. The phone on the other end changes the electrical energy into sound energy.

A car uses stored chemical energy in gasoline to move. The engine changes the chemical energy into heat and kinetic energy to power the car.

A toaster changes electrical energy into heat energy.

A television changes electrical energy into light and sound energy.

Heat Energy

Heat is a form of energy. We use it for a lot of things like warming our homes and cooking our food.

Heat energy moves in three ways:

1. Conduction
2. Convection
3. Radiation

Conduction is when energy is passed directly from one item to another. If you stirred a pan of soup on the stove with a metal spoon, the spoon will heat up. The heat is being conducted from the hot area of the soup to the colder area of spoon.

Metals are excellent conductors of heat energy. Other things like wood or plastics are not good conductors of heat energy. These "bad" conductors are called insulators. That's why a pan is usually made of metal and the handle is made of a strong plastic.

Convection is the movement of gases or liquids from a cooler spot to a warmer spot. If the soup pan above was made of glass, we could see the movement of convection currents in the pan. The warmer soup moves up from the heated area at the bottom of the pan to the top where it is cooler. The cooler soup then moves to take the warmer soup's place. The movement is in a circular pattern within the pan (see picture above).

Wind is often caused by convection currents. During the daytime, cool air from over water moves to replace the warm air over land that rises. During the nighttime, the directions changes and the water is warmer and the land is cooler.

Radiation is the final form of movement of heat energy. The sun's light and heat cannot reach us by conduction or convention because space is almost completely empty. There is nothing to transfer the energy from the sun to the earth. The sun's rays travel in straight lines called heat rays. When it moves like that, it is called radiation.

When the sun light hits the earth, its radiation is absorbed or reflected. Darker surfaces absorb more of the radiation and lighter surfaces reflect the radiation. So, if you wear light or white clothes outside during the summer, you would be cooler.

Here's What We Learned

1. Energy is the ability to do work.

2. There are two different types of energy. Kinetic energy is energy in motion. Potential energy is energy that is stored.

3. Energy is measured in units, two of which are Btu (British thermal unit) or joule.

4. Energy cannot be created, nor can it be destroyed. It can only be changed in form.

5. Heat energy comes in three forms: conduction, convection and radiation.

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Go To Chapter 2: What Is Electricity?

The Energy Story

Chapter 2: What is Electricity?

The Energy Story

Chapter 3: Generators, Turbines and Power Plants

The Energy Story

Chapter 4: Geothermal Energy

The Energy Story

Chapter 5: Fossil Fuels - Coal, Oil and Natural Gas

Where Fossil Fuels Come From

There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds millions of years ago before the time of the dinosaurs -- hence the name fossil fuels. The age they were formed is called the Carboniferous period, getting its name from carbon the basic element in coal and other fossil fuels.

Fossil fuels are made up of decomposed plant and animal matter. Plants change energy they receive from the sun into stored energy. This energy is food used by the plant. This is called photosynthesis. Animals eat plants to make energy. And people eat animals and plants to get energy to do work.

When plants and other ancient creatures died, they decomposed and became buried, layer upon layer under the ground. It took millions of years to form these layers into a hard, black colored rock-like substance called coal, a thick liquid called oil or petroleum, and natural gas. Fossil fuels can be found under the earth in many locations around the country. In California, we have oil and natural gas resources.

Each of the fossil fuels is extracted out of the ground differently.

Coal used in power plants is not found in California but is abundant in other states. It is mined in deep mines or in strip mines closer to the surface and brought to California to power a few small power plants.

Oil or Petroleum

To find oil and natural gas, companies drill through the earth to the deposits deep below the surface. The oil and natural gas are then pumped from below the ground by oil rigs (like in the picture above). They then usually travel through pipelines, like the ones in the picture to the right in Alaska.

Oil is found in 18 of the 58 counties in California. Kern County, the County where Bakersfield is found, is one of the largest oil production places in the country. But we only get one-half of our oil from California wells. The rest comes from Alaska, and a small amount comes from other countries. This oil is brought to California by large tanker ships. The petroleum or crude oil must be changed or refined into other products before it can be used.

Refineries

Oil is stored in large tanks until it is sent to various places to be used.

Oil is also made into many different products -- fertilizers for farms, the clothes you wear, the toothbrush you use, the plastic bottle that holds your milk, the plastic pen that you write with. They all came from oil.

There are thousands of other products that come from oil. Almost all plastic comes originally from oil. Can you think of some things made from oil?

At oil refineries, crude oil is split into various types of products by heating the thick black oil.

The products include gasoline, diesel fuel, aviation fuel, home heating oil, oil for ships and oil to burn in power plants to make electricity.

But in California, 74 percent of our oil is used for transportation -- cars, planes, trucks, buses and motorcycles. We'll learn more about transportation energy in Chapter 13.

Natural Gas

Natural gas is also found in California. We use more than what is found in California. So, we also bring natural gas to California from other states and from Canada.

Natural gas is lighter than air. Natural gas is mostly made up of a gas called methane. Methane is a simple chemical compound that is made up of carbon and hydrogen atoms. It's chemical formula is CH4. This gas is highly flammable.

Natural gas is usually found near petroleum underground. The natural gas is pumped from below ground and sent in large pipelines like the ones to the right.

Natural gas usually has no odor and you can't see it. Before it is sent to the pipelines and storage tanks, it is mixed with a chemical that gives a strong odor. The odor smells almost like rotten eggs. The odor makes it easy to smell if there is a leak.

From the storage tanks natural gas is sent through underground pipes to your home to cook your food and heat your house. Natural gas is also sent to factories and to power plants to make electricity. We'll learn more about the pipelines in California in Chapter 12.

Saving Fossil Fuels

Fossil fuels take millions of years to make. We are using up the fuels that were made more than 65 million years ago in the time of the dinosaurs. Once they are gone they are gone.

So, it's best to not waste fossil fuels. They are not renewable; they can't really be made again.

We can save fossil fuels by conserving energy.

We'll learn more about saving energy in Chapter 14.

Here's What We Learned

1. Fossil fuels were formed during the time of the dinosaurs when plants and animals died. Their decomposed remains gradually changed over the years to make coal, oil and natural gas.

2. Fossil fuels are usually found below ground and must be either dug out (like coal) or pumped from below the ground (like oil and natural gas).

3. California produces about one-half of the oil it uses. The rest comes from Alaska and other countries.

4. Oil is transported in huge pipelines and tanker ships to places where it is made into other products.

5. Many products, like plastic and fertilizer come from oil.

6. Natural gas is found near oil.

7. Natural gas is sent through a series of pipes until it comes to our homes, schools and businesses.

8. Fossil fuels are not renewable. They can't be remade.

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Go To Chapter 6: Hydro Power

The Energy Story

Chapter 6: Hydro Power

When it rains in hills and mountains, the water becomes streams and rivers that run down to the ocean. The moving or falling water can be used to do work. Energy, you'll remember is the ability to do work. So moving water, which has kinetic energy, can be used as a source of energy.

For hundreds of years, moving water was used to turn wooden wheels that were attached to grinding wheels to grind flour or corn. Today, moving water can also be used to make electricity.

Hydro means water. Hydro-electric means making electricity from water power.

Hydroelectric power uses the kinetic energy of moving water to make electricity. Dams can be built to stop the flow of a river. Water behind a dam often forms a reservoir. Dams are also built across larger rivers but no reservoir is made. The river is simply sent through a hydroelectric power plant.

The water flows through a pipe called a penstock and pushes against blades in a turbine, causing them to turn. The turbine is similar to the kind used in a power plant that we learned about in Chapter 3. But instead of using steam to turn the turbine, water is used.

The turbine spins a generator to produce electricity. The electricity can then go to your home, to your school, to factories and businesses.

Hydro power today can be found in the mountainous areas of California where there are reservoirs and along major rivers.

Here's What We Learned

1. Hydro power uses the kinetic energy of moving water.

2. The moving water can be used to turn wheels to grind grains or in a hydroelectric power plant to make electricity.

3. Moving water goes through a turbine spinning the shaft, which turns a generator to make electricity.

4. California's hydroelectric power plants are found along dams on rivers and in the mountains.

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Go To Chapter 7: Nuclear Energy - Fission and Fusion

ÝÝÝThe Energy Story

ÝÝÝChapter 7: Nuclear Energy - Fission and Fusion

This equation says:

E [energy] equals m [mass] times c² [c stands for the speed of light. c² means c times c, or the speed of light raised to the second power -- or c-squared.]

Please note that some web browser software may not show an exponent (raising something to a power, a mathematical expression) on the Internet. Normally c-squared is shown with a smaller "2" placed above and to the right of the c.

Scientists used Einstein's famous equation as the key to unlock atomic energy and also create atomic bombs.

The ancient Greeks said the smallest part of nature is an atom. But they did not know 2,000 years ago about nature's even smaller parts.

As we learned in chapter 2, atoms are made up of smaller particles -- a nucleus of protons and neutrons, surrounded by electrons which swirl around the nucleus much like the earth revolves around the sun.

Nuclear Fission

An atom's nucleus can be split apart. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it makes a tremendous explosion in an atomic bomb. The word fission means to split apart.

A nuclear power plant (like Diablo Canyon Nuclear Plant shown on the right) uses uranium as a "fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor.

Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction.

In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast.

If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor.

The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome in the picture is designed to keep this material inside if an accident happens.

This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy.

This water from around the nuclear core is sent to another section of the power plant. Here it heats another set of pipes filled with water to make steam. The steam in this second set of pipes powers a turbine to generate electricity.

Learn more about nuclear fission by visiting other web sites:

• Uranium Information Centre (Australia)

Nuclear Fusion

Another form of nuclear energy is called fusion. Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. The sun uses nuclear fusion of hydrogen atoms into helium atoms. This gives off heat and light and other radiation.

In the picture to the right, two types of hydrogen atoms, deuterium and tritium, combine to make a helium atom and an extra particle called a neutron.

Also given off in this fusion reaction is energy! Thanks to the University of California, Berkeley for the picture.

Scientists have been working on controlling nuclear fusion for a long time, trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to control the reaction in a contained space.

What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun.

You can learn more about nuclear fusion by visiting other locations on the Internet. The locations are:

• General Atomics Fusion Education Program
• Joint European Torus Project - Introduction to Fusion
• University of California, Berkeley

Here's What We Learned

1. Nuclear fission means splitting an atom apart.

2. Splitting an atom releases heat and light energy.

3. In a nuclear power plant, an atomic chain reaction is controlled to produce heat to boil water. That water boils water in pipes to make steam to turn a turbine and a generator to make electricity.

4. Nuclear fusion means combines atomic nuclei to make a larger nucleus.

5. The sun uses nuclear fusion of hydrogen into helium to make light and heat energy.

6. Scientists are trying to create nuclear fusion to make a cleaner source of power.

Links to other nuclear web sites

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Go To Chapter 8: Ocean Energy

The Energy Story

Chapter 8: Ocean Energy

The world's ocean may eventually provide us with energy to power our homes and businesses. Right now, most ocean energy power plants are only experimental and are fairly small. But how can we get energy from the ocean?

There are three basic ways to tap the ocean for its energy. We can use the ocean's waves, we can use the ocean's high and low tides, or we can use temperature differences in the water. Let's take a look at each.

Wave Energy

Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In this simple example, to the right, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine which can turn a generator.

When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.

This is only one type of wave-energy system. Others actually use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator.

Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house.

Tidal Energy

Another form of ocean energy is called tidal energy. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.

In order for this to work well, you need large increases in tides. An increase of at least 16 feet between low tide to high tide is needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea. One plant in France makes enough energy from tides to power 240,000 homes.

Ocean Thermal Energy

The final ocean energy idea uses temperature differences in the ocean. If you ever went swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It's warmer on the surface because sunlight warms the water. But below the surface, the ocean gets very cold. That's why scuba divers wear wet suits when they dive down deep. Their wet suits trapped their body heat to keep them warm.

Power plants can be built that use this difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the warmer surface water and the colder deep ocean water.

Using this type of energy source is called Ocean Thermal Energy Conversion or OTEC. It is being used in both Japan and in Hawaii in some demonstration projects.

Here's What We Learned

1. The ocean's energy can be used three basic ways.

2. Wave energy systems use the up and down motion of waves to turn a turbine and/or generator.

3. Tide energy systems traps high tides in a reservoir. When the tide drops, the water behind the reservoir can flow through a power plant, just like a regular hydroelectric plant.

4. Ocean thermal energy conversion uses the difference in temperature between warm surface water and cold deep ocean water to make electricity.

Related web site:ÝÝ Converting Wave Energy into Electricity

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Go To Chapter 9: Solar Energy

The Energy Story

Chapter 9: Solar Energy

When we hang laundry outside to dry in the sun, we are using the sun's heat to do work -- drying our clothes.

The sun has always been an energy source.

Plants use the sun's light to make food. Animals eat plants for food.

And as we found out earlier, decaying plants and animals millions of years ago produced the coal, oil and natural gas that we use today.

So, fossil fuels actually got their start as sunlight many millions of years ago.

The sun can also be used to heat water for hot water in our homes and businesses.

Solar Hot Water

In the 1890s solar water heaters were first used in California. They proved to be a big improvement over wood and coal-burning stoves. Artificial gas made from coal was available too to heat water. But it cost 10 times the price we pay for natural gas today. And electricity was even more expensive!

Many homes used solar water heaters. In 1897, 30 percent of the homes in Pasadena, just east of Los Angeles, were equipped with solar water heaters. As mechanical improvements were made, solar systems were used in Arizona, Florida and many other sunny parts of the United States.

By 1920, thousands of solar water heaters had been sold. But by then, large deposits of oil and natural gas were discovered in the western United States. As these low cost fuels became available, solar systems began to be replaced with heaters using fossil fuels.

Today, solar water heaters are making a come back. There are more than half a million of them in California alone! They heat water for use inside homes and businesses. They also heat swimming pools like in the picture.

Panels on the roof of a building, like this one on the right, contain water pipes. When the sun hits the panels and the pipes, the sunlight warms them.

That warmed water can then be used in a swimming pool.

Solar Thermal Electricity

Solar can also be used to make electricity.

Some solar power plants, like the one in the picture to the right in California's Mojave Desert, use a highly curved mirror called a parabolic trough to focus the sunlight on a pipe running down a central point above the curve of the mirror. The mirror focusses the sunlight to strike the pipe, and it gets so hot that it can boil water into steam. That steam can then be used to turn a turbine to make electricity.

In California's Mojave desert, there are huge rows solar mirrors arranged in what's called "solar thermal power plants" that use this idea to make electricity for more than 350,000 homes. The problem with solar energy is that it works only when the sun is shining. So, on cloudy days and at night, the power plants can't create energy. Some solar plants, are a hybrid technology. During the daytime they use the sun. At night they use natural gas to boil the water so they can continue to make electricity.

Another form of solar power plants to make electricity is called a Central Tower Power Plant, like the one to the right.

Sunlight is reflected off 1,800 mirrors circling the tall tower. The mirrors are called heliostats and turn to face the sun all day long.

The light is reflected back to the top of the tower in the center of the circle where a fluid is turned very hot by the sun's rays. That fluid can be used to boil water to make steam to turn a turbine and a generator.

This experimental power plant is called Solar II. It is being re-built in California's desert using newer technologies than when it was first built in the early 1980s. Solar II will use the sunlight to change heat into mechanical energy in the turbine.

The power plant will make enough electricity to power about 10,000 homes. Scientists say larger central tower power plants will be able to make electricity for 100,000 to 200,000 homes.

Solar Cells or Photovoltaic Energy

We can also change the sunlight directly to electricity using solar cells.

Solar cells are also called photovoltaic cells -- or PV cells for short -- and can be found on many small appliances, like calculators, and even on spacecraft. They were first developed in the 1950s for use on U.S. space satellites. They are made of silicon, a special type of melted sand.

When sunlight strikes the solar cell, electrons (red circles) are knocked loose. They move toward the treated front surface (dark blue color). An electron imbalance is created between the front and back. When the two surfaces are joined by a connector, like a wire, a current of electricity occurs between the negative and positive sides.

These individual solar cells are arranged together in a PV module. Some of the modules are set on special tracking devices to follow sunlight all day long.

The electrical energy from solar cells can then be used directly. It can be used in a home for lights and appliances. It can be used in a business. Solar energy can be stored in batteries to light a roadside billboard at night. Or the energy can be stored in a battery for an emergency roadside cellular telephone when no telephone wires are around.

Some experimental cars also use PV cells. They convert sunlight directly into energy to power electric motors on the car.

Here's What We Learned

1. Sunlight has always been a source of energy for plants, animals and humans. We use sunlight and heat from the sun to dry clothes outside.

2. The sun's heat can be used to warm water flowing through pipes on a roof. More than 500,000 solar water heating systems are used in California.

3. Sunlight can also be focussed in a solar thermal system to heat water or other fluids to make steam. The steam can be used to turn turbines to make electricity.

4. Sunlight can be used directly in solar cells or PV cells to make electricity.

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Go To Chapter 10: Wind Energy

The Energy Story

Chapter 10: Wind Energy

Wind can be used to do work.

The kinetic energy of the wind can be changed into other forms of energy, either mechanical energy or electrical energy.

When a boat lifts a sail, it is using wind energy to push it through the water. This is one form of work.

Farmers have been using wind energy for many years to pump water from wells using windmills like the one on the right.

In Holland, windmills have been used for centuries to pump water from low-lying areas.

Wind is also used to turn large grinding stones to grind wheat or corn, just like a water wheel is turned by water power.

Today, the wind is also used to make electricity.

Blowing wind spins the blades on a wind turbine -- just like a large toy pinwheel. The blades are attached to a hub that is mounted on a turning shaft. The shaft goes through a gear transmission box where the turning speed is increased. The transmission is attached to a high speed shaft which turns a generator that makes electricity.

If the wind gets too high, the turbine has a brake that will keep the blades from turning and being damaged.

We have many windy areas in California. The only problem with wind is that it is not windy all year long. It is usually windier during the summer months when wind rushes inland from cooler areas, like the ocean to replace hot rising air in California's warm central valleys and deserts.

And wind speeds must be above 12 to 14 miles per hour to turn the turbines fast enough to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. A kilowatt is 1,000 watts (kilo means 1,000). You can light ten 100 watt light bulbs with 1,000 watts. So, a 300 kilowatt (300,000 watts) wind turbine could light up 3,000 light bulbs that use 100 watts.

As of 1995, there were 13,437 wind turbines in California. These turbines are grouped together in what are called wind "farms." Theses wind farms are located mostly in the three windiest areas of the state:

• Altamont Pass east of San Francisco
• San Gorgonio Pass near Palm Springs
• Tehachapi south of Bakersfield

Together these three places make enough electricity to supply an entire city the size of San Francisco with power! About 30 percent of the world's wind-generated electricity is found in California. Other countries that use a lot of wind energy are Denmark and Germany.

But once electricity is made, it has to get from the wind turbines to our homes, factories and schools. The electricity transmission system is discussed in our next chapter.

Here's What We Learned

1. Wind energy can be used to do work.

2. Wind has been used for many years to drive boats and in windmills to grind grains or pump water.

3. Wind turbines are being used today to make electricity.

4. Wind spins the large blades which turn generators inside the turbine to make electricity.

5. California's nearly 13,500 wind turbines can supply enough electricity to power an entire city.

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Go To Chapter 11: Electricity Transmission System

The Energy Story

Chapter 14: Biomass Energy

The Energy Story

Chapter 15: Saving Energy and Energy Conservation

Some of the energy we can use is called renewable energy. These include solar, wind, geothermal and hydro. These types of energy are constantly being renewed or restored.

But many of the other forms of energy we use in our homes and cars are not being replenished. Fossil fuels took millions of years to create. They cannot be made over night.

And there are finite or limited amounts of these non-renewable energy sources. That means they cannot be renewed or replenished. Once they are gone they cannot be used again. So, we must all do our part in saving as much energy as we can.

In your home, you can save energy by turning off appliances, TVs and radios that are not being used, watched or listened to.

You can turn off lights when no one is in the room.

By putting insulation in walls and attics, we can reduce the amount of energy it takes to heat or cool our homes.

Insulating a home is like putting on a sweater or jacket when we're cold...instead of turning up the heat.

The outer layers trap the heat inside, keeping it nice and warm.

To make all of our newspapers, aluminum cans, plastic bottles and other goods takes lots of energy.

Recycling these items -- grinding them up and reusing the material again -- uses less energy than it takes to make them from brand new, raw material.

So, we must all recycle as much as we can.

We can also save energy in our cars and trucks.

Make sure the tires are properly inflated.

A car that is tuned up, has clean air and oil filters, and is running right will use less gasoline.

Don't over-load a car. For every extra 100 pounds, you cut your mileage by one mile per gallon.

When your parents buy a new car, tell them to compare the fuel efficiency of different models and buy a car that gets higher miles per gallon.

You can also save energy in your school.

Each week you can choose an energy monitor who will make sure energy is being used properly.

The energy monitor will turn off the lights during recess and after class.

You can make "Turn It Off" signs for hanging above the light switches to remind yourself.

You can start an Energy Patrol in your school. Click the words Energy Patrol to go to another location in our Internet site that tells you how to set one up in your school.

You can make sure your classmates recycle all aluminum cans and plastic bottles, and make sure the library is recycling the newspapers and the school is recycling its paper.

Conclusion
To make sure we have plenty of energy in the future, it's up to all of us to use energy wisely.

We must all conserve energy and use it efficiently. It also up to those of you who will want to create the new energy technologies of the future.

One of you might be another Albert Einstein and find a new source of energy. It's up to all of us. The future is ours but we need energy to get there.

Related web sites:ÝÝ Generating New Ideas for Meeting Future Energy Needs

Steckborn, Switzerland. First church in the world with with solar power

Switzerland. Solar power for agriculture

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Solar energy is produced through the use of solar cells. A solar, or photovoltaic, cell is a device that converts direct sunlight into electricity. The cells consist of two layers of material. One is treated to make it negative (n-type), and the other is treated to make it positive (p-type). The area where the two layers touch is called the p-n junction. As sunlight penetrates to the p-n junction, positive and negative charges from the two layers cross the junction, creating a flow of electric current. Diagram Then the energy is stored by batteries for future use. ²⁵

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The Electric Hookup

Objectives

The student will do the following:

1. Determine the wattage of various household appliances.
2. Calculate the number of kilowatt-hours used by appliances.
3. Identify the need to limit the use of appliances to conserve energy.
4. Identify costs per kilowatt-hour (kWh) of appliances.

Time: 3 class periods (over 2 weeks)

Materials: student sheets (included)

Background

A list of all the energy-using appliances and equipment in an average American home would show why it is estimated that a well-equipped home consumes as much as 35,000,000 British thermal units (BTU) of energy each year to operate. Considering that much of this energy is wasted, a great opportunity for energy conservation exists.

The first step toward conservation is to gain a better understanding of the energy consumption of each appliance or piece of equipment. An appliance's wattage is an indicator of how much electricity is used while operating the appliance. An appliance requiring 1,000 watts would use one kilowatt-hour of electricity during one hour of operation. For example, the average mixer uses 127 watts. This 127 watts divided by 1000 watts/kilowatt-hour of operation equals 0.127 kilowatt-hour. If the mixer is used for 6 minutes, 0.0127 kilowatt-hour of electricity has been used.

Procedure

1. Introduce the activity by sharing with the class the information in the background section above.
2. Distribute the student sheet "Wattage Ratings," included. Have the students bring in wattage ratings from various appliances around their homes. Ask each student to choose appliances that use different amounts of energy and that produce different kinds of energy from the electricity they use (e.g., heat, sound, or motion). Caution the students not to move large appliances by themselves to obtain wattage ratings. Have them seek permission and aid from parents to locate wattage rating information. (Check the owner's manuals before moving appliances.) Use appliances in the school as examples. Students may be assigned different equipment to ensure a wide range and thorough investigation of household appliances. Student sheet answers (in terms of kilowatt-hours of energy required) may be expanded to annual use by determining daily or weekly use and multiplying. If you prefer, use the student sheet "APPLIANCE ENERGY USE," included.
3. Distribute the student sheet "HOW TO READ YOUR METER," included.
   1. Tell the students to record daily meter readings at home for two weeks, and then to bring in an old utility bill along with the data they will have accumulated.
   2. Review the information recorded on their utility bills. Then, have each student calculate the charge per kilowatt-hour by dividing the energy charge by the number of kilowatt-hours used in his/her home for that month's bill. (Be sure to use only the energy charge; do not include other fees the utility may assess.) Typical residential rates in the Valley region average less than $0.06 per kWh.
   3. Have each student relate the amount spent on one month's electric bill to something that is pertinent to his/her own life. For example, students may relate the electric bill to car payments, the cost of music tapes, stereo equipment, schoolbooks, or athletic shoes. Solicit several examples from the class.
4. After completing the activities on the student sheets, distribute the student sheet "MAKING CHOICES" included. Are the students willing to change their habits and attitudes, and possibly their lifestyles, to conserve energy?
5. Continue with the follow-up below.

Follow-Up

1. Discuss the negative feelings the students may have about conserving electrical energy. What are the negative aspects of conservation? (By now, the benefits should be obvious-saving money and resources.) Conservation often takes self-discipline, development of routine habits, imposing rules upon oneself, lifestyle changes, and changes in purchasing patterns. Oftentimes these things are not fun or easy for people to accept. What ways can the students think of to motivate themselves and others to conserve?
2. Discuss some practical ways in which students can improve energy conservation in their own homes. Ask, "In what area is your family conserving energy best?" (for example, turning off lights). Ask, "In what area is your family not conserving energy well?" (for example, leaving the TV on while no one is watching). Are any of the students' families involved in serious energy conservation efforts such as the use of solar water heaters, automatic timers on heating/cooling systems, high-efficiency appliances and/or lighting, or other innovative conservation methods? Can the students recommend effective conservation practices to their classmates?

Wattage Ratings

Student Sheet

Check four different appliances for their wattage ratings. Using the conversion to kilowatt-hours(kWh) calculate the electricity usage for each appliance.

Appliance: ____________

watts/1000 watts/kWh per hour of operation = ____________ kWh

Appliance: ____________

watts/1000 watts/kWh per hour of operation = ____________kWh

Appliance: ____________

watts/1000 watts/kWh per hour of operation = ____________kWh

Appliance: ____________

watts/1000 watts/kWh per hour of operation = ____________kWh

Appliance: ____________

watts/1000 watts/kWh per hour of operation = ____________kWh

Using the table below, see how much energy the appliances you checked consume in equivalents of oil or coal.

Appliance Energy Use

Think about burning ten 100-watt light bulbs for one hour. That's the amount of electricity equivalent to one kilowatt-hour. Just as you pay for gallons of gas, quarts of milk, and loaves of bread, you pay for kilowatt-hours of electricity.

The chart below shows the average number of kilowatt-hours of electricity that various appliances use.* If you are interested in how much it costs to operate one of these appliances for a month or a year contact your local utilities company.

Notes
* These figures are averages and will vary depending on the user's habits and lifestyle.

** Includes kWh for heating water used by appliance.

*** This value accounts for all hot water usage, including dish washing and clothes washing.

**** Heat only.

***** Based on 1,500 sq. ft house insulated to meet TVA standards for energy efficiency. If your house does not meet these standards it may use considerable more electricity during the heating and cooling seasons.

How to Read Your Meter

In order to read an electric meter you must read from left to right. You must also determine which way the hands are turning on each dial.

Example:

	The 1 is to the left side of the dial. This would indicate the hand is turning counter-clockwise.
	Here the 1 is the right side of the dial, indicating the hands turns clockwise.

Write down the number each hand has passed. This may not be the number nearest the hand. For instance, if the hand has passed the 4 and is almost to the 5, you still read it as 4. Write down the numbers in the same order as you read the dials from left to right.

In the example given, the reading is 46372. If the last reading was 45109, subtract 45109 from 46372. This will give you the number of kWh used.

That is all there is to reading a meter, with one exception. If a hand points straight at a number and you do not know if it has passed the number or not, then look at the dial to the right. Has its hand passed zero?

To analyze your family's electricity use, read your meter daily for about two weeks, at approximately the same time each day. Record the readings on the following table.

DAILY USE OF ELECTRICITY IN MY HOME

* Current kWh cost; e.g. $0.056 per kWh in 1990. MAKING CHOICES

Pretend that the government has announced that, because of an energy crisis, electricity will be rationed. According to a new regulation, homeowners will be permitted to own and use no more than 12 electrical items other than lighting and heating/air conditioning systems. Listed below are a variety of items, which use electricity and are often found in American homes. Choose the 12 items you feel would be most essential to you and rank them from 1 to 12 (1 being the most important, 12 the least). Be prepared to defend your choices.

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Energy: The Issue of Renewable Energy

Introduction

There has been considerable interest recently in the topic of renewable energy. This is primarily due to concerns about environmental damage (especially acid rain and global warming) resulting from the burning of nonrenewable fossil fuels. However, investing in renewable energy is controversial for several reasons. First, not all scientists agree on the degree of environmental damage that can be attributed to fossil fuels. Second, fossil fuels are relatively abundant and cheap energy sources, and have contributed significantly to economic growth. Abandoning inexpensive fossil fuels for more expensive renewable ones will have major economic ramifications. Your students will enjoy analyzing this interesting and controversial topic.

Learning Objectives

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C. Answers to Selected Teaching Activities

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Facts About Renewable Energy

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Introduction

In recent years, there has been a greater interest in the issue of energy, especially renewable energy. This interest has not been the result of rapidly increasing energy prices ó nonrenewable energy, including oil, is abundant and relatively inexpensive. Rather, the renewed interest has been because of environmental concerns, especially the burning of fossil fuels, which many believe contributes significantly to acid rain and global warming. Another factor contributing to the interest in energy issues is the realization of the United Statesí increasing dependence on foreign oil. This was highlighted by the war in the Persian Gulf.

Public policy issues involving energy have tremendous economic implications. To ensure wise public policy, citizens and decisiomnakers must not only understand basic facts about energy sources, but also must know how to apply basic economic concepts in their analysis of energy issues.

Energy Basics

MEASURING ENERGY: Energy can be defined as the capacity to do work. The unit of measurement used to express the heat contained in energy resources is called a British thermal unit or Btu. One Btu is the heat energy needed to raise the temperature of one pound of water one degree Fahrenheit. A Btu is quite small. For example, if allowed to burn completely, a wooden kitchen match gives off one Btu of energy. A quad is used to measure very large amounts of energy. A quad is equal to one quadrillion (1,OOO,OOO,OOO,OOO,OOO) Btuís. The United States uses an enormous amount of energy ó about one quad of energy eveiy 4.5 days!

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U.S. Consumption of Primary Energy (1991)

Nuclear 8.0%

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TRENDS IN UNITED STATES ENERGY CONSUMPTION: As the economy and population of the United States have grown, so has energy consumption. However, this increase has been marked by remarkable increases in energy efficiency. For example, in 1989, the United States used about 9 percent more energy that it did in 1973; however, the value of the nationís real gross domestic product GDP (the total value of all the goods and services produced in the economy in a year) was 46 percent higher! The United States has improved its energy/GDP ratio as fast or faster than other developed countries. This improvement in energy efficiency was largely a response to the rapid increases in crude oil prices in the 1970s.

Renewable Energy Sources

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Biomass: Biomass is any organic substance that can be used as an energy source. The most common examples are wood, crops, seaweed, and animal wastes. Biomass has been used for thousands of years and is the oldest known energy source. It is a renewable energy source because its supply is unlimited ó more can always be grown in a relatively short time.

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Economic Implications

The issue of the development of renewable energy sources is a complicated one. The key point to remember is that there is an opportunity cost to every economic decision. Using tax revenues to subsidize renewable energy means giving up some other valuable use for those revenues. In energy policy, as in all public policy, decision makers must consider all the opportunity costs when determining trade-offs among different policy goals.

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Wind Energy
energy that comes from the movement of air

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Overview

Some of the key economics concepts in this unit are described below in the "Important Concepts to Emphasize" and "Facts About Renewable Energy" sections. Teachers may also wish to review the basic economic concepts relating to energy and the environment explained in the htroduction of this curriculum.

1. Subsidies are not always stated explicitly in dollars. They can be hidden and hard to measure in money terms. A subsidy exists whenever one person or group receives something of value from another person or group without charge or expectation of compensation. A subsidy can take various forms, such as cash gifts, special tax credits to reduce tax liability below that of others in similar circumstances, or transfer of tangible or intangible property. For example, until recently, Congress provided an income tax credit for homeowners who took certain actions to increase the energy efficiency of their homes, or used renewable energy sources to reduce their dependence on fossil fuels.
   
2. There are no free sources of energy. Everything has an opportunity cost. Even sources such as wind and solar power, which are readily available, cannot be developed without diverting resources from other social priorities. As an example, wind generators in California produce renewable energy, but also kill eagles and other endangered birds of prey that occasionally fly into the equipment.
   
3. Conservation means more than just not using our natural resources. It means making sure that society gets the most out of all its scarce productive resources, including natural resources. For example, we want to conserve petroleum so that we get the maximum benefit from our finite supplies; however, if we never use it, it has no value to us. We should manage our scarce natural resources to provide the greatest net benefit to present and future generations combined, after considering all of the costs and benefits involved, including the environmental costs.
   
4. We will never run out of petroleum and other nonrenewable resources. This is not to say that we can continue to use these energy sources without thought for tomorrow. Rather, it means that as an energy source becomes increasingly scarce, its market price will rise, discouraging consumption and encouraging production of alternative energy sources. During the 19th century, whalers nearly drove some species of whales to extinction. As this happened, the market price of whales and whale products inevitably rose. Eventually, whale oil became so expensive that petroleum became commercially feasible as an energy source, and whale oil lamps were phased out in favor of cheaper kerosene. The whales were actually saved by the free market response to their increasing scarcity.
   
5. When people do not bear all of the costs of their actions, their decisions tend to be socially inefficient. We implicitly subsidize fossil fuels today whenever producers and consumers do not pay the full environmental costs of their actions. As an example, without environmental regulations, consumers in Indiana would not pay the full social cost of producing electricity. To the extent that fossil fuel-burning power plants in the midwest may contribute to acid rain in the northeast, consumers in Indiana receive a subsidy from the northeast by not paying the full environmental costs of their electricity. The economic reasons for restricting the use of high-sulfur coal is that producers and consumers who can shift the environmental damage to others have no incentive through the free market to use more expensive low-sulfur coal to generate power. Most of the benefits of using low-sulphur coal would go to other regions (the northeast and Canada), while the costs would be borne by midwesterners. Restricting the use of high sulphur coal would also have a very detrimental impact on the economics of states like Indiana, which have important coal mining industries.

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Teaching Suggestions:

In question 2, explain that oil prices are quoted in current year dollars. Using constant dollars would give a truer picture of the real (inflation adjusted) changes in oil prices. Have some of your students determine the constant dollar prices of these oil prices. To do this they must use the implicit price deflator (IPD), an index number used by economists to figure constant dollar (real) price changes. The IPD for each year since 1973 is given below, using 1987 as the base year (IPD = 100). To determine the real constant dollar price of oil for any year, use this formula:

Constant Dollar Price = (Current Price/IPD) x 100

For example, in 1973 the current dollar price was $2 a barrel. The constant dollar (real) price is $2/41.3 x 100 = $4.84. In other words, the $2 price in 1973 is equivalent to $4.84 using inflated 1987 dollars. Have students figure and graph the real oil prices. Discuss how this graph differs from the graph of current dollar prices.

Implicit Price Deflators (1973-1990)

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1. Ask all the students to read background materials on energy: Assign half of the students to serve as Senators who will listen to testimony and then vote on the bill to give tax breaks to developers of renewable energy sources. The other half of the class should be divided into small groups representing some or all of the following groups: (1) fossil fuel producers and consumers, (2) developers of solar, wind, and geothermal power, (3) environmental groups, and (4) consumers in areas such as New England, which has good potential for hydro power, but depends on midwestern coal and OPEC petroleum.
2. Each special interest group should fill out a Decision Worksheet and Decision Grid reflecting its perspective on the problem. Each group should then elect a spokesperson to provide testimony in the Senate Hearings.
3. After hearing from the affected groups, members of the Senate should develop a consensus decision worksheet and vote on the energy bill.
4. In a debriefing session, ask students to defend their positions as either special interest groups or Senators voting on the issue.

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Key Questions to Ask Students:

1. What is a subsidy? (financial assistance provided by a person or group to another person or group, in the form of cash, tax breaks, or the transfer of something of value without payment)
2. What is a tax credit? (a tax break or rebate in the form of a special reduction in taxes that otherwise would have been due by an individual taxpayer or class of taxpayers)
3. Why are there not free sources of energy? (nothing is free, in the sense that everything has an opportunity cost, represented by the next best alternative that was given up in making a choice)
4. Why should solar energy companies care that fossil fuels can damage the environment? (solar companies feel that getting to use the environment for free represents a subsidy for fossil fuels that lowers their price below the full social cost, making it hard for nonpolluting energy sources to compete)
5. What is the difference between a renewable and a nonrenewable energy resource? (unlike renewable energy resources such as sunlight, water power, and wind, nonrenewable energy resources exist in finite quantities that cannot be replaced when they are used up)
6. If petroleum is a nonrenewable resource, how can it be that we will never run out? (as oil gets harder to extract from increasingly less productive deposits, the price will rise, and both consumers and producers will have incentives to find cheaper alternatives)

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Renewable Energy Basics

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Part A: The table below lists United States primary energy consumption by source in 1973 and 1991.

Primary Energy Consumption (percent)

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PART B: The data below shows the amount of electricity generated in the United States in 1990 by various renewable energy sources.

1990 United States Renewable Electric Generating Capacity (Gigawatts)

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4. Which renewable energy source above is used the least? __________________________________________________________________________________

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Trends In R & D Spending

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DOE Renewable Energy R & D Funding

($ millions, 1982 dollars)

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Energy Efficiency

1. Define energy efficiency. _________________________________________

1973 Total --74.3
l974 Total --72.5
1975 Total --70.5
1976 Total --74.4
1977 Total --76.3
1978 Total --78.1
1979 Total --78.9
1980 Total --75.9
1981 Total --74.0
1982 Total --70.8
1983 Total --70.5
1984 Total --74.1
1985 Total --74.0
1986 Total --74.3
1987 Total --76.9
1988 Total --80.2
1989 Total --81.3
1990 Total --81.3
1991 Total --81.1

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a. What was the increase in consumption from 1973 to 1991? __________________

b. Compute the percentage increase from 1973 to 1991. ________________________

5. The United States consumes more energy per unit of GDP than Japan or Italy (In 1988: United States ó 18.0 thousand Btuís, Japan ó11.2, Italy 13.6). Give at least two reasons for this difference
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Further Investigations

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Debating the Issues

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EEE Actions: You Can Make A Difference!

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The Case of the Energy Subsidy

3. Fill out a Decision Worksheet and Decision-Making Grid to help you come to a decision. Much depends on you. Good luck.

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SCENARIO

Senator Barnhartís proposal received mixed reviews in the Senate. Senators from the five top oil producing statesóTexas, Alaska, Louisiana, California. and Oklahoma ó expressed concern that the bill would put oil producers at a disadvantage that could result in serious job losses in their states. Three of those states, Texas, Louisiana, and Oklahoma, are also the top producers of natural gas, leading their senators to argue even more strongly against a subsidy for competing renewable fuels. Noting that renewable fuels are not yet competitive in price without tax subsidies, they argue that consumers would get the best product at the lowest price by letting the market determine what type of energy to produce and in what quantities. In addition, they object to any programs that would increase the size of the federal budget deficit at a time when program cuts and tax hikes are being proposed to deal with the out-of-control federal budget.

The president of the Sierra Club, Belinda Arbuckle disagreed. "For free markets to operate effectively, people need to pay the full cost of their actions. Our failure to take into account the full long-run costs of fossil fuels to society makes it difficult for producers of renewable energy sources to compete. I proposed new taxes on fossil fuels reflecting the environmental damage associated with their production and use. This would tend to increase the cost of fossil fuels reflecting their environmental impact and making it easier for renewable energy sources to compete on the basis of price."

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Activity 1: Renewable Energy Basics

4. The primary disadvantage of fossil fuels is that they are more polluting than renewable energy sources. The burning of fossil fuels also produces carbon dioxide, which some fear is causing global warming. This, however, is only a theory, and has not been confirmed by scientific evidence.

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5. Answers will vary.

Activity 3: Trends In R & D Spending

4. Oil prices rose sharply in the 1970s. They then plunged in the mid-1980s, before increasing again at the end of the decade. The increase in R & D is explained by the observed dramatic rise in oil prices in the 1970s; the decrease in R & D parallels the fall in oil prices. Increases in R & D spending in FY91 can be partly explained by environmental concerns of burning fossil fuels.

Activity 4: Energy Efficiency

b. 6.8/74.3 = 9.15 percent

5. "Energy efficiency" is a commonly used statistic to make comparisons among countries; however, it can be misleading since it does not take into account differences in life styles, population density, industry mix, and other factors. For example, Japan and Italy are small countries with high population densities. This makes energy-saving mass transit more practical. Italy and Japan also tax energy much more heavily (In Italy gas costs about $4 a gallon, of which $3 is tax!), which reduces energy consumption. The United States has a more extreme climate, which requires large amounts of energy for heating and cooling. Living standards also are higher in the United States, and it takes more energy to heat our larger homes. When corrected for differences in living space, the United States is among the most efficient of the other developed countries in residential heating. Another factor is that because energy is relatively abundant in the United States compared to Japan and Italy, we have developed industries that rely on high energy usage ("energy intensity") in production.

Activity 8: Case Study: The Case of the Energy Subsidy

The Case of the Energy Subsidy

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Source: Indiana Department of Education, Energy Environment & Economics

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Cheaper Heat Ý Ý Ý < live > Ý Nearly half of all the energy used in our homes is wasted. Heating and cooling inefficiencies are the major cause, and the prevention is, in many cases, simple and inexpensive. Here are some easy, do-it-yourself solutions for making your home more comfortable and less expensive to heat.

Draft Check
A simple way to locate outside air coming into your home is with a stick of incense. Light the incense and inspect your home, from the inside, for air leaks. Choose a breezy day, and go around windows, areas where plumbing and wiring go through walls, attic doors, entry doors and fireplace dampers. How much the smoke drifts horizontally will reveal how serious the leak is.
Most leaks can be quickly plugged with exterior silicone caulk - be sure to caulk the leaks from the outside of the house, or moisture will build up inside the walls. Weatherstripping and door sweeps will fix the door leaks quickly and easily.

• Use 'faced' fiberglass insulation (one side is papered over) to keep the fiberglass particles out of the air. Cut strips of insulation 3" longer than the circumference of the heater. Wrap them horizontally around the heater and seal with vinyl duct tape.
• Using a razor knife, cut away around thermostat controls, drain faucets and vents.
• If your heater is gas powered, do not cover the burner access. Leave three inches of exposed area around the flue collar.
• If you have an electric heater, cut a circle of insulation and fit it over the top, cutting slits for the pipes to go through. Seal any exposed fiberglass with duct tape.

• Shut off the pilot light during the summer months.
• If furnace has a fan belt, inspect for cracks or wear, and replace if nesessary. Be sure to shut off electricity at switch and at circuit breaker before inspecting fan belt.
• Keep vents and air returns clear of obstructions.
• Check chimney and furnace vent system once a year. Pipe should be securely connected, with no signs of corrosion or damage. Chimney and flue should be clear of obstructions.
• Keep the area around the furnace clear. Nothing should be leaning against it.
• Have furnace serviced regularly to be sure it's working at peak efficiency.

Vent Fireplace
When the wood fireplace isn't in use, close the damper to prevent warm air from escaping out the chimney, and ensure the damper fits tightly. Most importantly, provide outside combustion air directly to the fireplace by installing a small vent to the outside wall. This vent can also be installed through the floor, if fireplace is on the ground floor with an unheated crawlspace below. The vent can be screened to keep out bugs, but should be checked annually to clear any cobwebs building against the screen and reducing its air flow.
Remember that natural gas fireplaces are more economical, and provide more heat and less pollution, than wood burning units

Standard: 3600-07 Students will understand the flow of energy into and out of Earth systems
Objective: 3600-0702 Analyze the transfer of energy within Earth systems
ILO's: #1a) Make observations and measurements #2e) Analyze data and draw warranted inferences #5c) Understand science concepts and principles #6d) Construct tables and graphs

Absorption and Reflection of Solar Energy

Category:Learning Cycle

Learning Objectives:

1. The student will observe and explain absorption and reflection.
2. The student will compare energy conversions of cities with the country
3. The student will complete and interpret a graph of scientific data.

Materials, equipment and/or facilities:
You will need the following for each group of students performing the lab:

• Four laboratory thermometers
• white construction paper
• black construction paper
• aluminum foil
• four plastic cups
• graph paper
• colored pencils

Sequence and duration of each part of lesson:
Time: about 40 minutes

Exploration: Organize the students in pairs

Student Procedure:

Each pair of students should:

1. Cover each cup with a different material-white paper, black construction paper, aluminum foil, and one with no covering.
2. Fill each plastic cup two-thirds full of water.
3. Place a thermometer in each cup.
4. Place all four containers in sunlight for thirty minutes.
5. Take temperature readings initially and every five minutes. Write down data on your data table.
6. Plot each container's data on the same graph (temperature vs. time) in a different color.

Concept Invention:
Looking at your graph write answers to the following questions.

1. What are the temperature readings for each of the containers when you started? How do they compare?
2. What are the temperature readings for each container at the end of the time? How do they compare?
3. What happened to the sunlight?
4. What evidence do you have that sunlight was reflected or absorbed?
5. If all of the cups received the same amount of sunlight then how can you explain why they have different temperatures?

In a discussion ask students to apply their knowledge about how the various materials reflect and absorb sunlight in every day situations.
For example: white clothing in Africa, colors of cars, mirrored windows, silver backed light fixtures, etc.

Applications:
Knowing what you know about energy conversions:

1. Why is it usually cooler in the country than it is in the city?
2. If plants absorb sunlight why isn't there as much heat produced?
3. If the Law of Conservation of Energy states that energy cannot be created or destroyed then what energy conversion is taking place in plants to use up that extra energy?

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Energy-Efficient Homes

Objectives

The students will do the following:

1. Use models to learn how to maximize the comfort-conditioning of a home.
2. Observe, gather, and analyze data from the model simulations.
3. Draw conclusions from the data

Subjects:

General Science, Physical Science

Time:

4 class periods (Activities 3 and 4 can be activities for the whole class, and each requires one class period)

Materials:

large newsprint pad, drawing paper, several colored pens, rulers, protractor, student sheets (included)

Activity 3 - cardboard box, piece of white posterboard, compass, clear plastic wrap, flat black paint or black construction paper, thermometer, masking tape

Activity 4 - hot plate, watch, metal stem thermometer (0-100^o C), large beaker, º" thick plywood, ‡" thick fiberglass, ceramic tile, 2 plastic straws of different diameter, tape

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Background Information

Among the factors influencing the energy efficiency of home design are site analysis, home orientation, configuration, envelope, space planning, ventilation, heating, cooling, lighting and appliances, water heating, and waste management A brief explanation of each of these factors follows.

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Site analysis is the recognition and use of natural elements of a homeís setting for its energy efficiency. An example might be siting a home to take advantage of wind breaks to the north.

Home orientation includes facing a house and planning its windows to maximize solar heat gain in winter and minimize it in summer.

The home designís configuration should balance the benefits of using natural lighting and minimizing perimeter wall areas. To increase southern exposures (i.e, solar access), the optimal configuration is generally a form elongated in the east-west direction.

Envelope considerations include the glass and exterior wall materials selected, as well as structural design

Good space planning arranges various home activity areas appropriately. For example, the kitchen/dayrooms might share the east/south sides of the home.

Ventilation includes the controlled intake of fresh air, its circulation, and its exhaust

Heating needs in Tennessee Valley homes are usually greater than cooling needs. Home heating generally consumes more energy than any other home energy use (approximately 40 percent). Heating systems include electric resistance heating (e g, electric wall heaters), gas furnaces, wood heaters, and electric heat pumps. Central heating systems deliver heated air or water to all parts of the home. Heating (and cooling) systems are usually controlled by a thermostat.

Cooling systems in Tennessee Valley homes are almost always window or central air-conditioners that use a compressor and refrigerant to cool and dehumidify the air in side the home.

Lights and appliances are usually powered by electricity. An exception would be gas stoves. Well-designed windows or skylights can be used to provide "daylighting." One factor to consider when purchasing appliances is their energy efficiency rating. The location of appliances within the living space and the ways in which they are used and maintained must also be considered.

Domestic hot water is the term for heated water used for washing and bathing. As much as 25 percent of an all-electric homeís electricity bill comes from heating water.

Energy waste management should always be considered in the design of large buildings. Waste management systems for homes are generally rudimentary. An insulation blanket for a water heater is a simple form of waste management. Another is the fresh air intake control device on heating/air conditioning systems. We will begin to see more frequent use of air-to-air heat exchangers to preheat incoming fresh air as a waste management feature in new systems.

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Procedure

I. Give each student a copy of the student sheet "ENERGY-EFFICIENT STRUCTURES-Introduction" included. Using the background information, introduce the eleven factors given for energy-efficient homes to the students.

II. Divide the class into nine to eleven groups. Assign each group one of the student activities and give the members of the groups the student sheets for their activities. They are to complete the activities and then develop a presentation for the class based on their findings. Encourage them to do further research and to make visual aids. Tell them that their job is to convince their classmates to conserve energy.

III. Allow at least four class periods to complete this activity.

A Allow one period for students to learn about the eleven factors for energy efficient homes

B. Allow one period for students to complete their group assignments and plan their class presentations.

C. Two periods, after the groups have had a chance to do research or make visual aids, will be needed for presentations. Be sure to tell the groups how much time they have for their presentations (e g five minutes per group).

IV. You may wish to reserve the "CONFIGURATION" and "ENVELOPE" activities for whole-class participation. In this case, there would only be nine activity groups. Allow one class period for each of these two activities.

V. Continue with the follow-up below.

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Follow-Up

I. After the class presentations, some effort should be made to compare design features recommended by individual groups for the same design element. For example, compare the south-facing window placement and areas specified by the space planning, ventilation, and configuration groups.

II. You may wish to have a representative from your local utility company, a solar energy advocacy group, or a building or architectural firm visit your class.

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Resources

American Institute of Architects Energy Conservation in Building Design. N p . Author, 1974.

Edison Electric Institute. "Energy Management in the Home." N.p.: Author, [1987].

Mazria, E. The Passive Solar Energy Book Emmaus, PA Rodale, 1979

Tennessee Valley Authority. Energy Saver Home Standards. N.p: Author, [1981].

Introduction

Energy-efficient structures result from careful consideration of the following design factors

1. Site Analysis
2. Home Orientation
3. Configuration
4. Envelope
5. Space Planning
6. Ventilation
7. Heating
8. Cooling
9. Lighting and Appliances
10. Domestic Hot Water
11. Energy Waste Management

All-electric homes in the Tennessee Valley tend to consume the following relative amounts of electricity for the consumption categories listed:

Heating 44%
Domestic hot water 22%
Cooling 12%
Lighting 10%
Refrigeration 5%
Cooking 4%
Clothes drying 3%

Of course these percentages will vary as locations, homes, heating/cooling systems, appliances, and even the residentsí habits vary.

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Assignment

Each group is to complete the student activity sheet assigned to it and then develop a presentation to be given to the class. First you will meet as a group to discuss how your assignment is to be completed. Then plan your group presentation. Try to be innovative in the ways you present your findings. Use examples from your own homes and school buildings.

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Activity 1: Site Analysis

Homes should be sited to take advantage of natural features of the terrain, which offer energy conservation help. For example, a home site may offer windbreaks or summer shade. You have probably heard how one can use the sunís energy to heat a home. To benefit from the winter sunís heat, trees near the south wall of your home should be deciduous. Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, you may gather additional information to substantiate your conclusions.

1. List terrain features that can help to make a home more energy efficient.

2. Explain how each feature can contribute to energy efficiency.

3. Visit the site of a new house or housing development. Examine the siting of the home(s). Draw a map showing compass directions, a new home, and natural features that make the new home more energy efficient. The map need not be elaborate. Hereís an example:

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4. Describe the new home

5. Using a different color pen, add to your map the landscaping changes you would make to improve the homeís energy efficiency

Activity 2: Home Orientation

The sun can help heat our homes in winter. If we use air-conditioning in summer, the sun can increase our energy use and bills unless we provide sun controls. Sun controls that might be used include (deciduous) shade trees, roof overhangs, windows blinds and drapes, and thermal insulation. If the south-facing glass area is limited to approximately 10 percent of the comfort-conditioned living space area in a house in the Tennessee Valley, there should be more winter energy savings than summer losses (i.e. a net decrease in annual energy used for heating and cooling). Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, you may get additional information to substantiate your conclusions.

1. List the uses of windows.
2. Think about the position of the sun relative to your location. Describe summer sun positions at daybreak, noon, and sunset. Describe winter sun positions at these same times.
3. If you were a real estate developer and you wished to develop a subdivision in which the homes are designed to maximize energy conservation, you would have to orient the houses properly. Draw a simple aerial map showing the compass directions and the meadows and hills where you will construct the "Sunny Acres" Subdivision. Draw the nearest road that leads into town
4. Now, plan the access streets that will lead to the main road and select the lot on which you will build your own new home.
5. Draw your new home on the map. Your map may look something like this one.
6. Mindful of your household activities and your intention to use heat from the sun, sketch a simple floor plan showing the walls, doors, and windows of your new home.
7. How will you prevent unwanted summer sun from entering the windows? How will you prevent heat loss through the windows during winter? Identify special features you wish to include.

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Activity 3: Configuration
This activity may be used with the whole class

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People have long been aware of the heating effects of the sun. Utilizing the sunís heat in the winter and avoiding it in the summer helps to cut down on heating and cooling costs. Structures can be designed to conserve energy in both winter and summer. This investigation considers the manipulation of a "roof overhang" to illustrate using a shading device to promote the natural cooling of a house.

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Perform the following procedure and log your data on the data sheet. Refer to the provided drawings for guidance. Be prepared to demonstrate this experimental procedure during the class presentation.

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1. Cut a hole in one side of a cardboard box. This will be a window. Make sure the window is placed closer to the top of the box than it is to the bottom.

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2. Paint all the inside surfaces of the box flat black (or cover them with black construction paper).

3. Cut a piece of white posterboard for the roof long enough to make sure the roof covers the entire box and extends over the edge to completely shade the window.

4. Use plastic wrap to cover and seal the hole in the side of the box. Tape the plastic around the edges.

5. Make a small hole toward the back of the box. The hole should be large enough to insert the thermometer. Make sure the bulb of the thermometer is measuring the air temperature in the box. It should not be in direct sunlight.

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6. Tape a ruler to the "roof" piece. This will allow you to easily measure the amount of roof overhang.

7. Set this model "house" up outside in direct sunlight around midday. The window should be facing south.

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8. Place the roof so that the window is completely shaded. Wait about 5 minutes (until the temperature has stabilized) and record the temperature in the box. Also record the air temperature outside the box.

9. Move the roof a few centimeters at a time, so that the window is shaded to the different degrees given in the data table. Each time record the temperature after it stabilizes. Do this until you have measured the temperature of the box when its window is in full sun. Be sure to measure and record the outside air temperature, too.

DATA TABLE

all of the window ______ cm __________ __________
3/4 of the window ______ cm __________ __________
1/2 of the window ______ cm __________ __________
l/4 of the window ______ cm __________ __________
none of the window ______ cm __________ __________

10. Estimate the width of roof overhang needed in the Tennessee Valley by sketching to scale the south wall (assume it is all window) and determining the roof overhang needed when the noon sun is 75 degrees above the horizon. For this exercise, assume the roof is a flat one as in the model.

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Discussion Questions

1. Is roof overhang important for north-facing windows? Would your answer be different if you were living in Australia?
2. From the estimate you made of roof overhang needed in this region, what can you deduce about the placement of deciduous shade trees to the south?
3. Think about the way the sun seems to move from east to west during a day. What can you say about shade tree placement to diminish afternoon ~

Activity 4: Envelope*

It is important to "weatherproof" a home, that is, to insulate, to caulk, and to weatherstrip doors and windows. Insulation is any material that slows the movement of heat from one place to another. It slows the flow of heat entering the house during the summer; it slows the flow of heat leaving the house in the winter. The effectiveness of insulation in slowing the flow of heat is measured in resistance or "R-value." The higher the R-value, the better the insulating potential. Both thickness and composition are important factors in insulating effectiveness. For example, fluffy fibrous insulations should not be compressed before or during installation. In this experiment you will compare the effects of both thickness and composition on insulating capability.

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CAUTION: This experiment should be done under your teacherís supervision.

1. Turn on the hot plate. If it has a warm setting, use it. Measure the stabilized hot plate temperature with a metal stem thermometer (0-100 ^oC) and record it in the data table.
2. Measure and record the thickness of the ceramic tile. Lay it on the hot plate.
3. Measure and record the tiles top surface temperature each minute for 5 minutes. Now take readings every 2 minutes for 10 minutes. Take a final reading 5 minutes later. Record all the temperatures in the data table. Remove the tile from the hot plate using heat-protective gloves.
4. Measure and record the thickness of a piece of plywood. Lay it on the hot plate. Record the temperatures as you did for the tile.
5. Measure and record the thickness of a piece of fibrous insulation bat. (If you are using fiberglass, wear gloves when handling it.) Heat the insulation, measuring and recording the insulationís top surface temperature after 3, 6, 9, 12, and 15 minutes.
6. As a home assignment, plot the surface temperatures of the tile, plywood, and insulation as a function of time. Which surfaceís temperature rises faster?
7. Place a beaker of water on the hot plate and heat it until the temperature of the water stabilizes. While the water is heating, make an insulating sheath by inserting a smaller diameter straw inside another one, folding the straws at their midpoint and wrapping tape around them to hold the ends together.
8. Insert the thermometer into one of the open ends of the straw sheath, and place the apparatus in the beaker of water. Use a watch to time how long it takes the temperature measured by the thermometer to equal the waterís temperature.
9. Turn off the hot plate.
10. Explain why the insulating sheath you made of straws worked.

*This activity may be used with the whole class.

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DATA TABLES

Stabilized Hot Plate Temperature ______

Ceramic tile

Insulation

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Water

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DISCUSSION QUESTIONS

How well does the tile conduct the heat of the hot plate? Would tile be useful as insulation? Why or why not? What about the plywood?

_____________________________________________________________

2. How do you think the thickness of the insulation bat affects its insulating ability?

_____________________________________________________________

_____________________________________________________________

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Activity 5: Space Planning

The sunís warmth and light can make a good house even better. Think about your own familyís activities and then design the interior room arrangement of an energy-efficient, passive solar home, performing the following procedure. Afterwards, at home or in the library, gather additional information.

1. Where in the house are family members in the morning, at mid-day, in the evening, and at night? What kind of space and comfort-conditioning do they need at these times?
   
2. Draw a floor plan, showing compass directions, for a new home. Lay out the general arrangement, locate doors and windows, and then partition the space into rooms and storage spaces. Donít forget the need for convenient emergency exits and good traffic flow patterns.
   
3. Suggest construction materials (e.g., wood paneling, brick, tile), wall colors (e.g., light, dark, warm, cool), and lighting types to maximize the convenience, comfort, and energy conservation of your floor plan.

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Activity 6: Ventilation

Home ventilation is the controlled intake of fresh air, its circulation, and its exhaust. Average home construction results in inside air being exchanged one time each hour. Tight construction can reduce this to perhaps one-half an air change per hour. Fresh air enters the house through windows, doors, intake louvers on comfort-conditioning equipment, and infiltration or leakage. Many new homes have kitchen and/or bathroom exhaust fans that tend to induce a flow of outside air by reducing inside pressure slightly. Outside air is sometimes supplied to the fireplace grate. Vents are always included in attic or crawl spaces to reduce humidity.

Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, gather additional information to substantiate your statements.

1. Draw the floor plan of a new house to approximate scale, noting on your drawing the compass directions and the length, width, and height of your home. (You need not show inside room partitioning unless the ceiling height in the house is not uniform). Calculate the amount of floorspace in the home and its total air volume. Relate the air volume to anticipated air changes.
   
2. Make a fairly complete list of the places where air leakage is likely. What are the remedies for each leak?
   
3. Discuss different types of windows and doors and rate them for their likelihood to cause air leakage.
   
4. Where could fixed glass windows (i.e., windows that donít open) be used effectively? Look up in the dictionary the word "clerestory," noting both its meaning and pronunciation. Clerestory windows are often used in conjunction with "cathedral" ceilings. They do one thing exceptionally well Can you think what that might be?
   
5. Describe what is meant by "cross-ventilation."

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Activity 7: Heating

Heating is very important in Tennessee Valley homes because we have many cold days and nights. Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, find information to substantiate your choice. You may be able to get a fast overview of heating system types by talking to a heating contractor.

1. Using the following outline, briefly describe some of the heating systems used in the Tennessee Valley. Give both their advantages and disadvantages.

   A. Room Heaters

   a. electric resistance

   b. wood

   c. gas

   d. oil

   e. coal solar

   B. Central Heating Systems (circulating heated water or warm air)

   a. electric resistance

   b. heat pump

   c. gas

   d. oil

   e. coal

   f. wood

2. Discuss the relative costs of these systems, their efficiencies, and their maintenance requirements.
   
3. Discuss the likely availabilities and costs of the above fuels during the lifetimes of these systems.
   
4. Select a heating system for a new Tennessee Valley home. If you were building a home for yourself, what kind(s) of heating would you use? Why⁷

Activity 8: Cooling

Homes in the Tennessee Valley often have window air-conditioners or central air-conditioning systems which use compressors and refrigerants to cool and dehumidify inside air. Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, gather additional information to substantiate your choice (You may want to talk with a cooling systems contractor for more information).

1. How would you describe the Tennessee Valleyís summer climate? Does it vary widely from east to west? If so, why? Does it vary widely from north to south?
2. Discuss what you know about relative humidity and compare the relative humidities of a steam bath or sauna, a summer baseball game, and a cave. What happens when warm, moist air is suddenly cooled? What happens when you go outside on a cool, breezy day with wet hair?
3. Air conditioners and heaters are usually controlled by thermostats. Do you know how your parents control their cooling system? Do family members agree on daily settings for the cooling system control? If no one will be home, is it economical to leave your air conditioner running?
4. What do you know about heat pumps? They can be thought of as reversible air conditioners, supplying cool air in summer and warm air in winter. Because they use refrigerants, heat pumps can absorb heat from cool air in winter effectively. (You wonít need to select a separate air conditioner if the "Heating" group selects a heat pump)
5. Compare the efficiency of different brands of air-conditioners. To do this, you will need to compare their Energy Efficiency Ratios (EER). The Energy Efficiency Ratio is defined as the rate at which the device removes heat from the surroundings. It is usually expressed in British thermal units (Btu) per hour divided by the rate of energy input (watts) required to operate the machine. Select a group member to call one or two appliance stores to find out what typical EERs are (note brand names also) and what the expected annual operating costs might be (they may not know this).
6. It is important not to have more air-conditioning capacity than is needed. It is better to have one that runs more and, in doing so, removes more humidity. Make sure the appliance dealers take the energy efficiency of your house into account when sizing a cooling system for it. Air conditioners are often rated in tons. A ton of air-conditioning is usually expressed as 12.000 Btu per hour. A window air conditioner may range in size from 3/4-ton to two tons. Find out what size was most often used in houses that are now 15 to 20 years old Find out what size is most often used in newly completed houses of about the same size.
7. Select a cooling system from among those you have researched.

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Activity 9: Lighting and Appliances

The category "Lighting and Appliances" usually accounts for just over 20 percent of the energy consumption in an average Tennessee Valley all-electric home. Typically the big three users are heating (44 percent), hot water (22 percent), and cooling (12 percent). Lighting consumes about 10 percent of the electricity used in a typical home. The lesser three are refrigeration (5 percent), cooking (4 percent), and clothes drying (3 percent). Your job is to select a new home lighting system, explore ways to select energy-efficient appliances, and make suggestions for managing home energy use wisely Perform the following procedure. Afterwards, at home or in the library, gather additional information to substantiate your conclusions.

1. Although sharp changes in light intensity should be avoided, adequate light should be directed to areas that especially need it, e.g. where people read, at a work bench, or on the kitchen counter Fluorescent lighting tends to be cooler than incandescent lighting and about twice as efficient. The term "cooler" means both cooler in terms of temperature and in having a cooler appearance to the eye. Mixing in some incandescent lighting produces a warmer, cheerier look. With these things in mind, and supplying personal knowledge and opinion, design a lighting system for a new home. Draw a sketch showing light fixture placement in the kitchen, the living room, and a bedroom. Try to decide what light-related qualities wall and floor coverings should have. Donít forget to consider window placement and how it will affect lighting needs.
   
2. Here are some estimates of the annual energy consumption of various appliances. The numbers are kilowatt hours.

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Select one appliance that uses a lot of energy and find out (1) if annual average energy use for different brands are available, (2) how three brands with the same features compare in energy consumption, and (3) if the number given in this table is reasonably accurate.

3. For the appliance selected, list some measures which, if followed, will reduce its energy consumption

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Activity 10: Domestic Hot Water

The average Tennessee Valley family uses approximately 5,400 kilowatthours of electricity in a year to heat water. Using your personal knowledge, perform the following procedure. Afterwards, at home or in the library, gather additional information to substantiate your conclusions.

1. Here are some ways to reduce the energy consumed by heating water:

a. Fix leaking faucets

b. Use shower flow restrictors.

c. Insulate your water heater.

d. Set the water heater thermostat at a lower temperature, if possible

e. Take showers instead of baths.

f. Take cooler showers and make them short.

g. Try washing clothes with cold water

Discuss these with other members of your group and with your parents. Check your own home for compliance.

2. List the advantages and disadvantages of the following kinds of water heaters (if you do not know how they work, find out):

a. electric water heater

b. gas water heater

c. heat pump water heater

d. simple solar preheater for water (water runs through a garden hose inside a solar
collector box before filling the water heater)

e. solar water heater

3. If an electric water heater uses 5,400 kilowatthours annually and a natural gas water heater uses 25,000 cubic feet of natural gas, determine how much each will cost to run annually. Your local gas and electric utilities can help you.

4. Select a water heater for a new home and explain your choice.

Activity 11: Energy Waste Management

Managing energy use and waste in the home can be a difficult subject to understand. Three important elements of energy waste management are preheating, heat exchanging, and recycling. Although these are most commonly though of as being practical for industries, large buildings (like schools and office buildings), and other large energy consumers, homeowners can benefit from energy waste management, too. From your personal knowledge, answer the following questions. Afterwards, at home or in the library, gather additional information for your presentation.

1. There are a few uses of preheating in the home. One example is a passive solar water heater that preheats water before filling the water heater with it. Another example is taking frozen food from the freezer and letting it thaw on its own before cooking it, this saves cooking time and energy. Can you think of any other examples of preheating?
2. A heat exchanger is a device by which heat is transferred from one material or fluid to another. For example, an automobile radiator is a heat exchanger by which a water/antifreeze mixture, used to cool the engine, loses waste engine heat to outside air forced through radiator passages. The water is cooled for re-use by outside air. However, most of the heat picked up by the outside air is not used. How does the automobile use some of it?
3. Are there heat exchangers in the house? How does the air conditioner cool household air? How does the heat pump heat inside air? What other heat exchange applications in the home can you list?
4. List materials used in or around the home that can be recycled. List materials found in your garbage can which can be recycled
5. Would you recommend any energy waste management systems for a new home? Rate their costs by using the following comparisons: (a) How would the systems compare in cost to a central heating and cooling system? (b) How would they compare in cost to a refrigerator? (c) How would they compare in cost to a water heater?

Solar

Ovens

Made

From

Pizza

Boxes

The pizza boxes were donated by Pizza Hut.

Thank you Pizza Hut of Berlin, Vermont!

Principles of Solar Box Cooker Design

By Mark Aalfs, Solar Cookers International
e-mail: aalfs@yahoo.com

The purpose of this paper is to summarize the basic principles that are used in the design of solar box cookers.

People use solar cookers primarily to cook food and pasteurize water, although additional uses are continually being developed. Numerous factors including access to materials, availability of traditional cooking fuels, climate, food preferences, cultural factors, and technical capabilities, affect people's approach to solar cooking.

With an understanding of basic principles of solar energy and access to simple materials such as cardboard, aluminum foil, and glass, one can build an effective solar cooking device. This paper outlines the basic principles of solar box cooker design and identifies a broad range of potentially useful construction materials.

These principles are presented in general terms so that they are applicable to a wide variety of design problems. Whether the need is to cook food, pasteurize water, or dry fish or grain; the basic principles of solar, heat transfer, and materials apply. We look forward to the application of a wide variety of materials and techniques as people make direct use of the sun's energy.

The following are the general concepts relevant to the design or modification of a solar box cooker:

Heat Principles
Materials Requirements
Design and Proportion
Solar Box Cooker Operation
Cultural Factors
Back to the top

HEAT PRINCIPLES

The basic purpose of a solar box cooker is to heat things up - cook food, purify water, and sterilize instruments - to mention a few.

A solar box cooks because the interior of the box is heated by the energy of the sun. Sunlight, both direct and reflected, enters the solar box through the glass or plastic top. It turns to heat energy when it is absorbed by the dark absorber plate and cooking pots. This heat input causes the temperature inside of the solar box cooker to rise until the heat loss of the cooker is equal to the solar heat gain. Temperatures sufficient for cooking food and pasteurizing water are easily achieved.

Given two boxes that have the same heat retention capabilities, the one that has more gain, from stronger sunlight or additional sunlight via a reflector, will be hotter inside.

Given two boxes that have equal heat gain, the one that has more heat retention capabilities - better insulated walls, bottom, and top - will reach a higher interior temperature.

The following heating principles will be considered first:

• Heat gain
• Heat loss
• Heat storage

Heat Principles: Heat gain, Heat loss, Heat storage | Materials Requirements
Design and Proportion | Solar Box Cooker Operation | Cultural Factors | To top

A. Heat gain

Greenhouse effect:Ý This effect results in the heating of enclosed spaces into which the sun shines through a transparent material such as glass or plastic. Visible light easily passes through the glass and is absorbed and reflected by materials within the enclosed space.

	The light energy that is absorbed by dark pots and the dark absorber plate underneath the pots is converted into longer wavelength heat energy and radiates from the interior materials. Most of this radiant energy, because it is of a longer wavelength, cannot pass back out through the glass and is therefore trapped within the enclosed space. The reflected light is either absorbed by other materials within the space or, because it doesn't change wavelength, passes back out through the glass. Critical to solar cooker performance, the heat that is collected by the dark metal absorber plate and pots is conducted through those materials to heat and cook the food.
	Glass orientation:Ý The more directly the glass faces the sun, the greater the solar heat gain. Although the glass is the same size on box 1 and box 2, more sun shines through the glass on box 2 because it faces the sun more directly. Note that box 2 also has more wall area through which to lose heat.
	Reflectors, additional gain:Ý Single or multiple reflectors bounce additional sunlight through the glass and into the solar box. This additional input of solar energy results in higher cooker temperatures.

Heat Principles: Heat gain, Heat loss, Heat storage | Materials Requirements
Design and Proportion | Solar Box Cooker Operation | Cultural Factors | To top

B. Heat loss

The Second Law of Thermodynamics states that heat always travels from hot to cold. Heat within a solar box cooker is lost in three fundamental ways: Conduction, Radiation, and Convection

Conduction:

The handle of a metal pan on a stove or fire becomes hot through the transfer of heat from the fire through the materials of the pan, to the materials of the handle. In the same way, heat within a solar box is lost when it travels through the molecules of tin foil, glass, cardboard, air, and insulation, to the air outside of the box.

The solar heated absorber plate conducts heat to the bottoms of the pots. To prevent loss of this heat via conduction through the bottom of the cooker, the absorber plate is raised from the bottom using small insulating spacers as in figure 6. Radiation: Things that are warm or hot -- fires, stoves, or pots and food within a solar box cooker -- give off heat waves, or radiate heat to their surroundings. These heat waves are radiated from warm objects through air or space. Most of the radiant heat given off by the warm pots within a solar box is reflected from the foil and glass back to the pots and bottom tray. Although the transparent glazings do trap most of the radiant heat, some does escape directly through the glazing. Glass traps radiant heat better than most plastics. Convection: Molecules of air move in and out of the box through cracks. They convect. Heated air molecules within a solar box escape, primarily through the cracks around the top lid, a side "oven door" opening, or construction imperfections. Cooler air from outside the box also enters through these openings.

C. Heat storage:

As the density and weight of the materials within the insulated shell of a solar box cooker increase, the capacity of the box to hold heat increases. The interior of a box including heavy materials such as rocks, bricks, heavy pans, water, or heavy foods will take longer to heat up because of this additional heat storage capacity. The incoming energy is stored as heat in these heavy materials, slowing down the heating of the air in the box.

These dense materials, charged with heat, will radiate that heat within the box, keeping it warm for a longer period at the day's end.

Heat Principles: Heat gain, Heat loss, Heat storage | Materials Requirements
Design and Proportion | Solar Box Cooker Operation | Cultural Factors | To top³⁴

Standard:3600-07
Objective: 3600-0702
ILO's: #1a. Make observations and measurements. d. Make predictions based on current knowledge. #2b. Formulate hypothesis. d. Collect and record data. e. Analyze data. g. Construct models and simulations. #4d. Recognize the personal relevance of science in daily life. e. Respect the contributions of science to the quality of life. #6d. Construct charts to summarize data.

Let the Sunshine In

Category:Experiment

Learning Objectives:

1. Students will predict the relative amount of the sun¹s heat which will flow through different window coverings.
2. Students will measure the amount of sunlight (heat) which flows though various window coverings by conducting a controlled simulation experiment.
3. Students will record their findings in the form of a chart.
4. Students will use their results to draw conclusions about the relative quality of each window covering based upon its ability to control heat flow.

Materials, equipment and/or facilities:

• Access to sunlight (outdoors preferable)
• Water
• White paper, Scissors, and Tape to cover beaker sides
• Small pieces (the size of beaker tops) of various window coverings such as:
  • screens
  • tinted shading (lens from sunglasses will work)
  • curtain materials (may use more than one type)
  • window blinds
  • vinyl window shade
  • glass (to represent double panes)
• Beaker for each type of covering
• Thermometer for each type of covering
• Writing utensil and paper for chart

Sequence and duration of each part of lesson:
Introduction: 5 to 10 Minutes
Ask students to list different window coverings which they have observed in their home, school, car, or other enclosed structures. Write their ideas on the board and then ask which covering they believe best limits the flow of heat. Which do they think keeps the inside of a home warmest/coolest in the summer/winter? Inform them that the following experiment will help them to answer these questions.

Set-up: 10 to 15 Minutes
Assign students to:

1. Fill each beaker to the same level (at least 3 cm.) with water.
2. Place a thermometer in each beaker.
3. Cover the sides with white paper.
4. Number them.
5. Cover the top of each beaker with one of the different window coverings.

Each student should construct a chart to record the beaker number, temperature of water for each beaker, and the type of window covering. Set the beakers in a sunny location.

Wait time: Approximately 30 Minutes
Time must be allowed for the water to absorb the heat energy from the sun that passes through the covering. During this period, a teacher may develop an original activity for students or may choose from the following:

1. Instruct students to construct a hypothesis for each beaker's relative heat absorption. Have them list the beakers in order from what they believe will be the coolest to the one they think will be warmest. They may even be asked to go a step further and predict how many degrees they believe the water temperature in each beaker will increase.

2. Travel around the school, observing and recording different window coverings, the position of windows relative to the sun's rays, and the relative temperature of the rooms near these windows.

Results and Conclusions: 10 to 15 Minutes
Return to the beakers. To insure uniformity, the teacher should read to the students the new temperature of the water in each beaker and have each student carefully record these results on their chart. Ask students to write their conclusions about which materials best control the flow of heat. Have them answer the following questions:

Which covering would keep an enclosed structure warmest/coolest in the summer/winter?
Which of your hypotheses were correct?

Evaluation: A teacher may determine whether or not the student objectives have been met through asking the questions in the conclusion sections.

Variations: Students may investigate the absorption of different colors or materials to determine which clothes might be best to wear in the summer or winter. They may also test the quality of various sunglass lenses or brands of sunscreen.

Sources

1.   Passive Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

2.   Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

3.   Solar Home MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

4.   Solar Collecting Panels MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

5.   Solar Heating MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

6.   Photovoltaic Cells MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

7.   Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

8.   Solar Maximum Mission MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

9.   "THE ENERGY STORY." http://www.energy.ca.gov/education/story/story-html/story.html (08/27/01 20:52:59)

10.   "THE ENERGY STORY: Chapter 1 - What Is Energy?." http://www.energy.ca.gov/education/story/story-html/chapter01.html (08/27/01 20:53:29)

11.   "THE ENERGY STORY: Chapter 2 - What Is Electricity?." http://www.energy.ca.gov/education/story/story-html/chapter02.html (08/27/01 20:53:56)

12.   "THE ENERGY STORY: Chapter 3 - Generators, Turbines and Power Plants." http://www.energy.ca.gov/education/story/story-html/chapter03.html (08/27/01 20:54:13)

13.   "THE ENERGY STORY: Chapter 4 - Geothermal Energy." http://www.energy.ca.gov/education/story/story-html/chapter04.html (08/27/01 20:55:04)

14.   "THE ENERGY STORY: Chapter 5 - Fossil Fuels - Coal, Oil and Natural Gas." http://www.energy.ca.gov/education/story/story-html/chapter05.html (08/27/01 20:55:17)

15.   "THE ENERGY STORY: Chapter 6 - Hydro Power." http://www.energy.ca.gov/education/story/story-html/chapter06.html (08/27/01 20:55:29)

16.   "THE ENERGY STORY: Chapter 7 - Nuclear Energy - Fission and Fusion." http://www.energy.ca.gov/education/story/story-html/chapter07.html (08/27/01 20:55:42)

17.   "THE ENERGY STORY: Chapter 8 - Ocean Energy." http://www.energy.ca.gov/education/story/story-html/chapter08.html (08/27/01 20:55:55)

18.   "THE ENERGY STORY: Chapter 9 - Solar Energy." http://www.energy.ca.gov/education/story/story-html/chapter09.html (08/27/01 20:56:09)

19.   "THE ENERGY STORY: Chapter 10 - Wind Energy." http://www.energy.ca.gov/education/story/story-html/chapter10.html (08/27/01 20:56:23)

20.   "THE ENERGY STORY: Chapter 14: Biomass Energy." http://www.energy.ca.gov/education/story/story-html/chapter14.html (08/27/01 20:57:48)

21.   "THE ENERGY STORY: Chapter 15 - Saving Energy and Energy Conservation." http://www.energy.ca.gov/education/story/story-html/chapter15.html (08/27/01 20:59:35)

22.   "SOLAR ENERGY." http://www.history.rochester.edu/class/solar/cells.htm (08/27/01 21:02:45)

23.   "SOLAR ENERGY." http://www.history.rochester.edu/class/solar/cells.htm (08/27/01 21:03:10)

24.   "Key Centre for Photovoltaic Engineering UNSW - Solar Cells." http://www.pv.unsw.edu.au/info/solarcel.html (08/27/01 21:08:19)

25.   "A Look at Solar Energy." http://www.utexas.edu/depts/grg/ustudent/gcraft/fall95/issues/ryan/ryan.html (08/27/01 21:14:48)

26.   http://www-lips.ece.utexas.edu/~delayman/CALSOL/IMAGES/c_dreamn.gif (08/27/01 21:16:32)

27.   http://www-lips.ece.utexas.edu/~delayman/solar/IMAGES/cstate_1.jpg (08/27/01 21:17:06)

28.   "Alliance to Save Energy -- The Electric Hookup Exercise." http://www.ase.org/educators/lessons/hookup.htm (08/27/01 21:19:07)

29.   "Energy: The Issue of Renewable Energy Lesson Plan." http://www.ase.org/educators/lessons/hs/renewable.htm (08/27/01 21:19:58)

30.   "Cheaper Heat." http://eartheasy.com/live_cheapheat.htm (08/27/01 21:20:25)

31.   "Absorption and Reflection of Solar Energy." http://www.wested.org/werc/earthsystems/energy/absorbtion.html (08/27/01 21:22:54)

32.   "Energy-Efficient Homes -- High School Lesson Plans." http://ase.org/educators/lessons/hs/eehome.htm (08/27/01 21:24:49)

33.   "Pizza Box Solar Cooker." http://www.eecs.umich.edu/~coalitn/sciedoutreach/funexperiments/agesubject/lessons/other/solar.html (08/27/01 21:25:35)

34.   "Principles of Solar Cooker Design." http://solarcooking.org/sbcdes.htm (08/27/01 21:27:17)

35.   "Let the Sunshine In." http://www.wested.org/werc/earthsystems/energy/sunshine.html (08/27/01 21:28:41)

Bibliography

"A Look at Solar Energy." http://www.utexas.edu/depts/grg/ustudent/gcraft/fall95/issues/ryan/ryan.html (08/27/01 21:14:48)

"Absorption and Reflection of Solar Energy." http://www.wested.org/werc/earthsystems/energy/absorbtion.html (08/27/01 21:22:54)

"Alliance to Save Energy -- The Electric Hookup Exercise." http://www.ase.org/educators/lessons/hookup.htm (08/27/01 21:19:07)

"Cheaper Heat." http://eartheasy.com/live_cheapheat.htm (08/27/01 21:20:25)

"Energy-Efficient Homes -- High School Lesson Plans." http://ase.org/educators/lessons/hs/eehome.htm (08/27/01 21:24:49)

"Energy: The Issue of Renewable Energy Lesson Plan." http://www.ase.org/educators/lessons/hs/renewable.htm (08/27/01 21:19:58)

"Key Centre for Photovoltaic Engineering UNSW - Solar Cells." http://www.pv.unsw.edu.au/info/solarcel.html (08/27/01 21:08:19)

"Let the Sunshine In." http://www.wested.org/werc/earthsystems/energy/sunshine.html (08/27/01 21:28:41)

"Pizza Box Solar Cooker." http://www.eecs.umich.edu/~coalitn/sciedoutreach/funexperiments/agesubject/lessons/other/solar.html (08/27/01 21:25:35)

"Principles of Solar Cooker Design." http://solarcooking.org/sbcdes.htm (08/27/01 21:27:17)

"SOLAR ENERGY." http://www.history.rochester.edu/class/solar/cells.htm (08/27/01 21:02:45)

"SOLAR ENERGY." http://www.history.rochester.edu/class/solar/cells.htm (08/27/01 21:03:10)

"THE ENERGY STORY." http://www.energy.ca.gov/education/story/story-html/story.html (08/27/01 20:52:59)

"THE ENERGY STORY: Chapter 1 - What Is Energy?." http://www.energy.ca.gov/education/story/story-html/chapter01.html (08/27/01 20:53:29)

"THE ENERGY STORY: Chapter 10 - Wind Energy." http://www.energy.ca.gov/education/story/story-html/chapter10.html (08/27/01 20:56:23)

"THE ENERGY STORY: Chapter 14: Biomass Energy." http://www.energy.ca.gov/education/story/story-html/chapter14.html (08/27/01 20:57:48)

"THE ENERGY STORY: Chapter 15 - Saving Energy and Energy Conservation." http://www.energy.ca.gov/education/story/story-html/chapter15.html (08/27/01 20:59:35)

"THE ENERGY STORY: Chapter 2 - What Is Electricity?." http://www.energy.ca.gov/education/story/story-html/chapter02.html (08/27/01 20:53:56)

"THE ENERGY STORY: Chapter 3 - Generators, Turbines and Power Plants." http://www.energy.ca.gov/education/story/story-html/chapter03.html (08/27/01 20:54:13)

"THE ENERGY STORY: Chapter 4 - Geothermal Energy." http://www.energy.ca.gov/education/story/story-html/chapter04.html (08/27/01 20:55:04)

"THE ENERGY STORY: Chapter 5 - Fossil Fuels - Coal, Oil and Natural Gas." http://www.energy.ca.gov/education/story/story-html/chapter05.html (08/27/01 20:55:17)

"THE ENERGY STORY: Chapter 6 - Hydro Power." http://www.energy.ca.gov/education/story/story-html/chapter06.html (08/27/01 20:55:29)

"THE ENERGY STORY: Chapter 7 - Nuclear Energy - Fission and Fusion." http://www.energy.ca.gov/education/story/story-html/chapter07.html (08/27/01 20:55:42)

"THE ENERGY STORY: Chapter 8 - Ocean Energy." http://www.energy.ca.gov/education/story/story-html/chapter08.html (08/27/01 20:55:55)

"THE ENERGY STORY: Chapter 9 - Solar Energy." http://www.energy.ca.gov/education/story/story-html/chapter09.html (08/27/01 20:56:09)

http://www-lips.ece.utexas.edu/~delayman/CALSOL/IMAGES/c_dreamn.gif (08/27/01 21:16:32)

http://www-lips.ece.utexas.edu/~delayman/solar/IMAGES/cstate_1.jpg (08/27/01 21:17:06)

Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Solar Heating MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Solar Home MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Photovoltaic Cells MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Solar Collecting Panels MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Passive Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Solar Maximum Mission MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Solar Energy MicrosoftÆ EncartaÆ Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.