Renewable Energy Sources:
Wind, Solar and Geothermal

This unit will explore renewable energy sources. You will learn about our current usage of renewable fuels and how they must be changed and adapted for our use. You will also discover the advantages and disadvantage of renewable energy sources. A discussion of the future of these alternative energy sources is included.

Scientists are working hard to find new ways to meet the world’s ever expanding need for energy. Look at the sources of energy we use today. Mostly we depend upon gas, oil, and coal, fossil fuels. The electricity in your house probably is generated at a power plant that relies heavily on coal. Our cars run on gas and we heat out homes with gas or oil or electric generated by coal.

We found in the last unit how long it took fossil fuels to form. Since these fossil fuels are nonrenewable resources we only have a limited amount to use. Some scientists predict that without decreasing our usage of fossil fuels they could be gone in as few as 100 years.

It is not hard to figure out that the world is simply not going to stop using energy so the solution is to find energy sources that are not limited, but renewable. In this lesson we will look at various types of renewable energy sources. These are not new energy sources. People all over the world have been using them for a very long time. Each source will have advantages, but also come with disadvantages. We will look at the availability of the source. We will look at the advantages and the disadvantages. Understanding all these parts together will help us make good decisions of how to use these sources for our energy needs.

Scientists will use problem solving to deal with the disadvantages and try to find solutions. The future is promising. Many new methods of energy generation are being tested, used and refined, not only in industry but in communities across the country. Some ideas are passive while other ideas are very complex. Read on to find out how alternative energy sources can help work out the shortage of energy.

Fuel Facts

Ø In 1850 91% of the US energy came from wood, a renewable resource, today 90% of the US energy comes from nonrenewable fossil fuels

Solar Energy

We have always used the energy of the sun as far back as humans have existed on this planet. Five thousand years ago, people "worshipped" the sun. Ra, the sun-god, was considered the first king of Egypt.

We know today, that the sun is simply our nearest star. Without it, life would not exist on our planet. We use the sun's energy every day in many different ways. When we hang laundry outside to dry in the sun, we are using the sun's heat to do work -- drying our clothes.

Plants use the sun's light to make food. Animals eat plants for food. Decaying plants hundreds of millions of years ago produced the coal, oil and natural gas that we use today. So, fossil fuel is actually sunlight stored millions and millions of years ago.

Indirectly, the sun or other stars are responsible for ALL our energy. Even nuclear energy comes from a star because the uranium atoms used in nuclear energy were created in the fury of a nova - a star exploding.

Let's look at ways in which we can use the sun's energy.

· Solar Hot Water

o In the 1890s solar water heaters were being used all over the United States. They proved to be a big improvement over wood and coal-burning stoves. Gas was available to heat water, but it was very, very expensive. And electricity was even more expensive. Some towns did not even have electricity.

o The picture shown here, on the right, is a solar water heater installed on the front roof of a house in California; in 1911 (the panels are circled above the four windows).

Improvements were made on solar heating systems in Arizona, Florida and many other sunny parts of the United States. By 1920, ten of thousands of solar water heaters had been sold. Then large deposits of oil and natural gas were discovered in the western United States. The cost of fuel became very low. Solar water systems began to be replaced with heaters that burned fossil fuels. Today, solar water heaters are making a comeback. They heat water for use inside homes, businesses and swimming pools.

Solar Thermal Electricity

Solar energy can also be used to make electricity. Some solar power plants use a curved mirror to focus the sunlight on a pipe running down a midpoint above the curve of the mirror. The mirror focuses 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.

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.

Scientists are working to solve this disadvantage. They can’t make the sun shine but they can use a "hybrid" technology. During the daytime they use the sun. At night and on cloudy days they burn natural gas to boil the water so they can continue to make electricity.

There are many other types of solar power plants being tested. Scientists say some types of larger solar power plants can 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. These are like sunshine batteries. The energy is stored in the cells or batteries but the energy comes from the sun, not a chemical reaction like in the AA Energizers in your walkman.

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.

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.

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 to make electricity.

For hundreds of years, moving water was used to turn wooden wheels to grind (or mill) flour or corn. These were called grist mills or water mills. Water can either go over the top of the wheel, or the wheel can be placed in the moving river. The flow of the river then turns the wheel.

In 1086 in southern England there were 5,624 waterwheel-driven mills. That was about one mill for each 400 people. 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 sometimes forms a reservoir.

Hydro is one of the largest producers of electricity in the United States. Water power supplies about 10 percent of the entire electricity that we use. In states with high mountains and lots of rivers, even more electricity if made by hydro power.

How a Hydro Dam Works

The water behind the dam flows through the intake opening and into a pipe. The water pushes against blades in a turbine (like fan blades), causing them to turn. The turbine spins a generator to produce electricity. The electricity can then travel over long distance electric lines to your home, to your school, to factories and businesses.

Hydro power today can be found in the mountainous areas of states where there are lakes and reservoirs and along rivers. The problem is that some parts of the country are not mountainous or near rivers.

Biomass
Biomass is matter usually thought of as garbage. Some of it is just stuff lying around -- dead trees, tree branches, yard clippings, left-over crops, wood chips, and bark and sawdust from lumber mills. It can even include used tires and livestock manure.

Your trash, paper products that can't be recycled into other paper products, and other household waste are normally sent to the dump. Your trash contains some types of biomass that can be reused. Recycling biomass for fuel and other uses cuts down on the need for "landfills" to hold garbage.

This stuff nobody seems to want can be used to produce electricity, heat, compost material or fuels. Composting material is decayed plant or food products mixed together in a compost pile and spread to help plants grow.

In California more than 60 million tons of biomass is produced each year. Of this, five million tons is now burned to make electricity. This is biomass from lumber mill wastes, urban wood waste, forest and agricultural residues and other feed stocks. If all 60 million tons of biomass was used it could make close to 2,000 megawatts of electricity. That's enough energy to make electricity for about two million homes!

How does biomass work?

How biomass works is very simple. The waste wood, tree branches and other scraps are gathered together in big trucks. The trucks bring the waste from factories and from farms to a biomass power plant. Here the biomass is dumped into huge containers. This is then fed into a furnace where it is burned. The heat is used to boil water in the boiler, and the energy in the steam is used to turn turbines and generators.

Biomass can also be tapped right at the landfill with burning waste products. When garbage decomposes, it gives off methane gas. You'll remember that natural gas is made up of methane. Pipelines are put into the landfills and the methane gas can be collected. It is then used in power plants to make electricity. This type of biomass is called landfill gas.

A similar thing can be done at animal feed lots. In places where lots of animals are raised, the animals - like cattle, cows and even chickens - produce manure. When manure decomposes, it also gives off methane gas similar to garbage. This gas can be burned right at the farm to make energy to run the farm.

Using biomass does not add to global warming. Plants use and store carbon dioxide (CO2) when they grow. This is then released when the plant material is burned. Other plants then use that released CO2 when they grow. So using biomass closes this cycle of storing carbon dioxide. Carbon dioxide is a gas that, when there's too much, can contribute to the "greenhouse effect" and global warming.

So, the use of biomass is environmentally friendly because the biomass is reduced, recycled and then reused. It is also a renewable resource because plants to make biomass can be grown over and over.

Today, new ways of using biomass are still being discovered. One way is to produce ethanol, a liquid alcohol fuel. Ethanol can be used in special types of cars that are made for using alcohol fuel instead of gasoline. The alcohol can also be combined with gasoline. This reduces our dependence on oil - a non-renewable fossil fuel.

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.

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 turn on a shaft that turns a generator that makes electricity.

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

Wind is blowing in all areas of the earth. The only problem with wind is that it is not windy all the time. In order for a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per hour. If the wind is blowing slower the turbines can’t spin fast enough to generate any electricity.

The turbines usually produce about 50 to 300 kilowatts of electricity each. A 300 kilowatt (300,000 watts) wind turbine could light up 3,000 light bulbs that use 100 watts!

Turbines are grouped together in what are called wind "farms." These wind farms are located mostly in the windiest areas of the state. About 11 percent of the entire world's wind-generated electricity is found in California. Other countries that use a lot of wind energy are Denmark and Germany.

Once electricity is made by the turbine, the electricity from the entire wind farm is collected together and sent through a transformer. There the voltage is increased to send it long distances over high power lines.

Geothermal

Geothermal Energy has been around for as long as the Earth has existed. "Geo" means earth, and "thermal" means heat. So, geothermal means earth-heat.

Have you ever cut a boiled egg in half? The egg is similar to how the earth looks like inside. The yellow yolk of the egg is like the core of the earth. The white part is the mantle of the earth. And the thin shell of the egg, that would have surrounded the boiled egg if you didn't peel it off, is like the earth's crust.

Below the crust of the earth, the top layer of the mantle is a hot liquid rock called magma. The crust of the earth floats on this liquid magma mantle. When magma breaks through the surface of the earth in a volcano, it is called lava.

For every 100 meters you go below ground, the temperature of the rock increases about 3 degrees Celsius. Or for every 328 feet below ground, the temperature increases 5.4 degrees Fahrenheit. So, if you went about 10,000 feet below ground, the temperature of the rock would be hot enough to boil water.

Deep under the surface, water sometimes makes its way close to the hot rock and turns into boiling hot water or into steam. The hot water can reach temperatures of more than 300 degrees Fahrenheit (148 degrees Celsius). This is hotter than boiling water (212 degrees F / 100 degrees C). It doesn't turn into steam because it is not in contact with the air. When this hot water comes up through a crack in the earth, we call it a hot spring, like Emerald Pool at Yellowstone National Park. Or, it sometimes explodes into the air as a geyser, like Old Faithful Geyser.

About 10,000 years ago, Paleo-Indians used hot springs in North American for cooking. Areas around hot springs were neutral zones. Warriors of fighting tribes would bathe together in peace. Every major hot spring in the United States can be associated with Native American tribes. California hot springs, like at the Geysers in the Napa area, were important and sacred areas to tribes from that area. In other places around the world, people used hot springs for rest and relaxation. The ancient Romans built elaborate buildings to enjoy hot baths, and the Japanese have enjoyed natural hot springs for centuries.

Geothermal Today

Today, people use the geo-thermally heated hot water in swimming pools and in health spas. Or, the hot water from below the ground can warm buildings for growing plants.

In San Bernardino, in Southern California, hot water from below ground is used to heat buildings during the winter. The hot water runs through miles of insulated pipes to dozens of public buildings. The City Hall, animal shelters, retirement homes, state agencies, a hotel and convention center are some of the buildings which are heated this way.

In the Country of Iceland, many of the buildings and even swimming pools in the capital of Reykjavik (RECK-yah-vick) and elsewhere are heated with geothermal hot water. The country has at least 25 active volcanoes and many hot springs and geysers.

Geothermal Electricity

Hot water or steam from below ground can also be used to make electricity in a geothermal power plant. Some of the areas have so much steam and hot water that it can be used to generate electricity. Holes are drilled into the ground and pipes lowered into the hot water, like a drinking straw in a soda. The hot steam or water comes up through these pipes from below ground.

A geothermal power plant is like in a regular power plant except that no fuel is burned to heat water into steam. The steam or hot water in a geothermal power plant is heated by the earth. It goes into a special turbine. The turbine blades spin and the shaft from the turbine is connected to a generator to make electricity. The steam then gets cooled off in a cooling tower. The cooled water can then be pumped back below ground to be reheated by the earth.

Geothermal / Ground Source Heat Pumps

Though it gets much hotter as we go deep below ground, the upper layer of the earth close to the surface is not very hot.

Almost everywhere across the entire planet, the upper 10 feet below ground level stays the same temperature, between 50 and 60 degrees Fahrenheit (10 and 16 degrees C). If you've ever been in a basement of a building or in a cavern below ground, the temperature of the area is almost always cool.

A geothermal or ground source heat pump system can use that constant temperature to heat or cool a building. Pipes are buried in the ground near the building. Inside these pipes a fluid, like the antifreeze in a car radiator, is circulated.

In winter, heat from the warmer ground goes through a heat pump, which sends warm air into the home or business. During hot weather, the process is reversed. Hot air from inside the building goes through the heat pump and the heat is passed into the relatively cooler ground. Heat removed during the summer can also be used to heat water.

Although we still rely heavily on fossil fuels there are other options that we can use to reduce our dependence on those fuels. By looking at the advantages and disadvantages of these alternatives we can make good decisions to be sure that we have the energy we need for the future.

ACITIVITY 1: Solar S’mores

Materials: Every two people will need:

4 graham crackers

16 mini marshmallows

2 plain milk chocolate candy bars

8-by-11-inch glass baking pan

a clear glass lid for the baking pan

1 thermometer

This is an outdoor experiment: need to have a place in direct sunlight (no shade) and where animals won’t come by to eat the ingredients or disturb the pan! Use your thermometer to see what temperature it is outside. You need to do this experiment when it is at least 85° F. If it isn’t hot enough outside, wait for a warmer day.

Activity Directions

1. Put four graham crackers side by side in the bottom of the glass baking pan.

2. Place a chocolate bar on top of two of the graham crackers.

3. Put 8 mini-marshmallows on top of the other two graham crackers.

4. Cover the baking pan with the clear glass lid.

5. Put the pan out in an area where it will get full sunlight—no shade!

6. Let the pan just sit there until the chocolate bars and marshmallows melt.

7. To make a S’More, put one chocolate and one marshmallow graham cracker together to make a sandwich. You should have two sandwiches. Enjoy!

8. You might repeat this experiment, but this time try lining the glass baking pan with aluminum foil and black construction paper. See if the marshmallows and chocolate melt faster than they did in the plain glass pan. If our hunch is right, and dark paper absorbs more sunlight and heat, we should find out the S’Mores melt faster than in the plain glass pan.