Energy From the Sun
In about forty minutes the sun sends to the earth's surface about as much energy as people use in a year. We use energy from the sun without being aware of it. The sun's energy melts snow, warms your body, and dries the laundry on a clothesline. On some days the sun makes the streets seem "hot enough to fry an egg."
Nearly every bit of energy used by humans comes from the sun's energy -- or solar energy. The wood we burn for heat and the fruits and vegetables we eat come from plants. These plants use sunlight to change water, minerals and carbon dioxide into plant material and food. Fossil fuels such as coal, oil and natural gas form by the deposit and decay of plants and organisms over millions of years. We can consider coal, natural gas, and oil to be "fossilized" or stored up solar energy.
Even the wind which powers sailboats and windmills is a result of the sun heating different parts of the earth's atmosphere at different rates. Hydroelectric power also depends on the sun to evaporate water into the atmosphere. Eventually this evaporated water changes to snow and rain and falls back to earth to fill our dams and reservoirs.
The Sun in the Sky
The diagram shows the earth rotates or spins around on its axis once every 24 hours. Earth also revolves around the sun once every year. Because the earth rotates, the position of the sun in the sky changes from sunrise to sunset.
Because the earth is tilted on its axis, the sun's position in the sky also changes from summer to winter as the earth moves around the sun.
The tilt of the earth on its axis also explains why sunlight is less strong in winter than in summer. The tilt causes the suns rays to reach the ground at a shallower angle in winter. This spreads the solar energy more thinly over the ground. In summer when the sun is more nearly overhead, more solar energy strikes the ground. In all of the United States except Hawaii, the sun appears in the southern half of the sky all year. Devices used to collect solar energy, or windows designed to let in solar energy must face the southern sky to make the best use of the sun's energy throughout the year.
Using Solar Energy to Heat Homes
Solar energy can heat homes in two ways: active and passive systems. Active solar heating systems use working (or active) parts such as pumps, fans, and solar collectors to collect and move solar heat around the home. The sketch below shows a house using an active solar heating system. To use solar energy, we must first find a way to collect it. The solar house in the sketch uses a metal solar collector. Dark-colored sheets of metal are placed on the roof of the house. The metal heats quickly, and the dark color
helps absorb energy from the sun. The solar collector faces the direction that gets the most sunlight. In the Northern Hemisphere, you would have a solar collector face south. You also can see in the sketch that a liquid circulates through pipes in a solar house. Solar energy heats the liquid as it moves through the solar collectors. The heated liquid then circulates to a water tank. There, the heat from the liquid is used to heat the water in the tank. Then, the cooled liquid returns to the solar collectors to absorb more solar energy. The heated water from the water tank is used to warm the air that moves through the house.
We can collect solar energy only when the sun shines. At night and on cloudy days, solar houses must use stored solar energy. You know that in the summer, rocks and stones get hot quickly and stay warm even when the sun sets. These materials store heat from the sun. A solar house has cement walls and floors that store heat. Also, the water tank stores water heated by solar energy. In these ways, stored solar energy can help keep the house warm even on a cloudy day. But after a few days of cool, cloudy weather, other energy sources must be used to keep the solar house warm.
Passive solar heating takes advantage of special design features of houses. These passive solar houses use the changing position in the sky. Specially designed solar homes let in the winter sun but exclude the hot summer sun. Using these special design features can reduce heating costs in the winter and air conditioning bills in the summer. The diagram shows the features of a passive solar house. They have large areas of glass facing south to allow sunlight to enter in winter. Heavy building materials such as brick and concrete store the heat and gradually release it inside the house. The walls and ceilings are well insulated. The insulation prevents heat from escaping outside in the winter, or entering in the house in summer. Wide eaves or other shading devices protect the south facing windows from the sun when it is high in the sky in summer. One of the good things about passive solar houses is that they need not cost any more to build than a regular house.
Active and Passive Solar Heating in Iowa
Solar energy already has an important place in the lives of many Iowans. As traditional energy sources become more expensive, and concern for the environment increases, solar energy might well play a growing role in Iowa's energy future.
There are more than 6,000 passive solar residential structures in Iowa. The amount that a structure benefits from the sun's energy depends on the structure's design. If all new single family homes were built to take advantage of solar energy, it is estimated that nearly $3,000,000 could be saved annually on natural gas used to heat homes. The number of active solar systems in Iowa is not known. There is potential for active solar systems to provide all the heat, or to help heat houses and small commercial buildings.
Think About It:
1. How do solar houses collect and store solar energy?
2. Why is solar energy a good energy source to use?
3. Challenge What might happen to the water in a garden hose if the hose lies in the sun all day?
Energy From the Wind
The wind can do work. People have used wind for centuries as an energy source for sailing ships, pumping water and grinding grain. More recently, wind has
become an important energy source for generating electricity. Interest in the use of wind energy is increasing as fossil fuels become more expensive. Environmental pollution caused by fossil fuels is also a very serious concern. Some scientists think windmills can someday produce almost one-tenth of our electricity. They are studying ways we can use windmills to meet more of our energy needs.
Wind machines like the one shown in the diagram are made up of three basic parts. The propeller is made up of a number of blades that catch the wind, causing the propeller to spin. The spinning blades turn a shaft connected to an electric generator. The generator makes electricity when there is enough wind to turn the propeller. The electricity can be used immediately or stored away in batteries to be used later. A tail device is used on smaller windmills to swing the propeller into the wind. Larger wind generators sometimes use motors to do this.
Like solar energy, the wind can be considered to be free. However special equipment is needed to use the energy from the wind. So, although the energy supply may be free, the cost of using wind energy is not.
The wind might be clean and free, but it is not a perfect energy source. When the wind is calm, windmills cannot produce electricity. Windmills are sometimes noisy and take up a lot of space that can be used for homes or farms. Some wind generators send out signals that interfere with radios and televisions. People living in different places will have to decide whether the wind is a good energy source for them to use.
Wind Energy in Iowa
The wind blowing over the hills and plains of Iowa might prove to be one of the state's most practical renewable energy resources. Wind energy was used largely on farms to pump water from wells. But in the 1930s and 1940s rural
electrification led to the end of that era of wind energy systems. Several things have led to an increased interest in the research and development of a new generation of wind technology. These include public interest in clean fuels, the rising cost of fossil fuel generated electricity, and increased awareness of environmental pollution.
California's wind energy farms like the one pictured here have been in operation for many years. But are such wind farms practical in Iowa? Researchers are currently collecting highly accurate wind speed data from key sites around the state. Highly detailed and accurate wind records measured 100 to 150 feet above the ground are needed. This information will help determine whether successful planning of wind farms in Iowa can take place.
In 1993, the Waverly, Iowa, Light and Power Company became the first municipal utility company in the Midwest to own and operate a wind turbine. This demonstration project will help Midwest utility companies determine if the cost of operating wind turbines is practical.
Two Iowa school districts have recently joined the list of users of wind generated electricity. In 1993, Spirit Lake in northwest Iowa became the first district to install a generator. A 250 kilowatt wind turbine was put into operation during the summer of that year. In December of 1993, a 250 kilowatt wind generator shown in the picture below was installed on the grounds of the Nevada Middle School.
Since that time the Nevada district has also installed a 200 kilowatt wind generator. School district estimate that Nevada's two generators will save the district about half of the annual electricity bill of $90,000. The two Nevada generators represent a gift worth about $500,000. Had the district purchased the generators on their own, it would have taken about ten years for the savings to pay for the turbines. Information learned about using wind generators at the Spirit Lake school and the Nevada schools is shared with the public. Studying these wind generator systems provides valuable information about the efficiency and cost of operation.
New technology is expected to produce a new generation of wind energy systems. These new wind energy systems are expected to generate electricity at low cost per kilowatt-hour. If these new wind generator systems get developed, then we might see wind farms in Iowa, alongside of agricultural crop farms.
Think About It:
1. What are the three essential parts of a wind machine?
2. What are several advantages of using wind energy? Several disadvantages?
3. Challenge What areas in your community might make good locations for a wind turbine? Explain why you picked these locations.
Who in the World Uses Solar and Wind Energy?
Some solar projects being studied in different parts of the world might someday generate electricity for many thousands of homes. Concentrating sunlight is one area of current research. Properly concentrating sunlight on a central point
produces extremely high temperatures. These temperatures range from hundreds to several thousand degrees Fahrenheit. This type of solar energy collector is called a concentrating collector. Two types of concentrating collectors are illustrated here. Trough collectors and point focus collectors use curved
sheets of reflective metal or mirrors. These materials reflect and concentrate sunlight onto a central pipe or point called the focal point. Trough collectors are being used in Australia to produce hot water in homes and industry. Research on point collectors continues in various locations around the world.
Concentrating collectors are being used to cook food in developing countries where firewood and electricity for cooking is scarce. A common type of solar cooker is a point focus collector about three feet across. It is aimed at the sun with a frying pan or saucepan suspended at the focal point. On a sunny day these solar cookers can boil a quart of water in about 15 minutes.
On a very large scale, a field of huge mirrors called heliostats reflect solar energy. Study the diagram below. Notice that the sun's energy reflects onto a central receiving tower or power tower. The reflected and concentrated sunlight boils water in the power tower. Steam from the boiling water turns the blades of a turbine. The turbine operates a generator that makes electricity. Power tower projects have been set up in Europe, Japan and near Albuquerque, New Mexico, in the United States.
Many new wind turbines are being developed to generate electricity. Many people live in remote areas of the world, far away from electric generating plants. Wind generators provide electricity for a lot of these people. Of course there must be a reliable source of wind energy for these wind generators to be practical.
Large individual wind generators are being developed in many countries including Great Britain, Sweden, Denmark, Germany, Canada and the United States. These generators add to existing electricity supplies. In the USA, the National Aeronautics and Space Administration (NASA) developed a 22,500 kilowatt machine in the state of Washington. The propeller is about 300 feet across and is attached to a tower that is nearly 200 feet high. New wind machines with propellers nearly 400 feet across have been developed!
Wind farms are large areas of land dotted with hundreds of wind generators. Current wind farms exist in 13 countries. The electricity produced on wind farms is usually fed directly into existing electric networks. The Altamont Pass, Tehachapi Mountains and San Gorgio Pass wind farms are the biggest and best known wind farms in the USA. Together they are able to produce more than 1,200,000 kilowatts of electricity from more than 1400 wind turbines. At times they supply enough electricity for 200,000 average homes in California.
Ebeltoff in Denmark built the first sea-based wind farm. It has sixteen 55 kilowatt wind turbines built on a jetty almost a half-mile long, plus a 100 kilowatt unit on the shore. These wind machines catch the wind as it blows from the sea. The sea-based wind farm supplies enough electricity for about 600 homes.
Think About It:
1. Describe how concentrating solar collectors work.
2. Why do you think very large wind turbines are being developed?
3. Challenge Solar collectors will not work very efficiently if they are not aimed directly at the sun. Think about what you know about the sun's position in the sky and how it changes. Use this knowledge to explain why a "tracking system" is used with concentrating collectors and heliostats.
Active and Passive Solar Heating in Iowa
1. Solar houses collect solar energy with solar collectors and large windows. Solar energy is stored in the cement walls of the house, along with being stored as hot water in a storage tank.
2. It is renewable and there is no pollution associated with its use.
3. The water will heat up.
Wind Energy in Iowa
1. The propellor, generator, and tail device.
2. Advantages -- clean and renewable. Disadvantages -- Noisy, not always practical or cost-efficient.
Who Uses Solar and Wind Energy?
1. Collect the sun's rays by reflecting them off of metal or mirrors onto a central line or focal point. It heats quickly.
2. Very large wind turbines can catch more wind to generate more electricity.
3. To be aimed directly at the sun, the collectors need to follow it as it moves from the eastern to the western sky. The tracking device allows this to happen.
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