# High School Earth Science/Renewable Energy Resources

What if we could have all of the energy we needed and never run out of it? What if we could use this energy without polluting the air and water? In the future, renewable sources of energy may be able to provide all of the energy we need. Some of these resources can give us "clean" energy that causes little or no pollution.
Plenty of clean energy is available for us to use. The largest amount of energy to reach Earth's surface is from solar radiation. Each year 174 petawatts (1.74×10$^{17}$ W) of energy from the sun enter the Earth's atmosphere. Because the planet's interior is hot, heat flows outward from the interior, providing about 23 terawatts (2.3×10$^{13}$ W) of energy per year. By contrast, the total world power consumption is around 16 terawatts (1.6×10$^{13}$ W) per year. So solar or geothermal energy alone could provide all of the energy needed for people if it could be harnessed.

## Lesson Objectives

* Describe different renewable resources, and understand why they are renewable.
* Understand that the sun is the source of most of Earth's energy.
* Describe how energy is carried from one place to another as heat and by moving objects.
* Understand how conduction, convection, and radiation transfer energy as heat when renewable energy sources are used.
* Understand that some renewable energy sources cost less than others and some cause less pollution than others.
* Explain how renewable energy resources are turned into useful forms of energy.
* Describe how the use of different renewable energy resources affects the environment.

## Solar Energy

When you think of the sun, you probably think of two things—light and heat. The sun is Earth's main source of energy, and light and heat are two different kinds of energy that the sun makes. The sun makes this energy when one element, called hydrogen, changes into another element, called helium. Changing hydrogen into helium releases huge amounts of energy. The energy travels to the Earth mostly as visible light. The light carries the energy through the empty space between the sun and the Earth in a process called radiation. We can use this light from the sun as an energy resource called solar energy (Figure 5.6).
Solar energy is a resource that has been used on a small scale for hundreds of years. Its use on a larger scale is just starting to ramp up and people increase production of renewable energy sources. One focus of solar power development in the United States is the desert southwest.
Solar power plants are in the works for southeastern California, near the California-Nevada border.
Solar energy is used to heat homes, to heat water, and to make electricity. Solar energy can be used to heat the water in your pool or to heat tile floors in your home. In recent years, scientists and engineers have found new ways to get more and more energy from this resource. Because there are many different uses for solar energy, there are also many different ways of turning the sun's energy into useful forms. One of the most common ways is by using solar cells. Solar cells are devices that can turn sunlight directly into electricity. You may have seen solar panels on roof tops. Lots of solar cells make up an individual solar panel.
Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver (Figure 5.7). When a liquid, such as oil or water, flows through this receiver, the focused sunlight heats the liquid to a high temperature. Then, this heated liquid transfers its heat by conduction. In conduction, energy moves between two objects that are in contact with one another. The object that is at a higher temperature transfers energy as heat to the object that is at a lower temperature. For example, when you heat a pot of water on a stove top, conduction causes energy to move from the pot to its metal handle, and the handle gets very hot. In the case of the solar power plant, the energy conducted by the heated liquid is used to make electricity.
Solar energy has many benefits. It does not produce any pollution. Also, there is plenty of it available. In fact, the amount of energy that reaches Earth from the sun every day is many times more than all of the energy we use. For this reason, we consider solar energy a renewable form of energy. For as long as sunlight continues to warm the Earth, we will never run out of this resource. One problem with solar energy is that it cannot be used at night, unless a special battery stores extra energy during the day for use at night. The technology for most uses of solar energy is still expensive. Until this technology becomes more affordable, most people will prefer to get their energy from other sources. As you learned earlier, most of the Earth's energy comes from the sun. Other renewable resources also come from the sun originally. You will be learning about these resources later in this lesson.

## Water Power

Earlier in this lesson, you learned that energy can travel in the form of light and heat, just as it does when it travels from the sun to the Earth. Now, you will learn about one way in which energy can travel in the form of a moving object. In this case, the moving object is water (Figure 5.8). Water power uses the energy of water in motion to make electricity. It is the most widely used form of renewable energy in the world, and it provides almost one fifth of the world's electricity.
In most power plants that use water power, a dam holds water back from where it would normally flow. Instead, the water is allowed to flow into a large turbine. Because the water is moving, it has energy of motion, called kinetic energy. The energy of this moving water makes the turbine spin. The turbine is connected to a generator, which makes electricity.
Many of the streams in the United States where water flows down a slope have probably been developed for hydroelectric power. This is a major source of California’s electricity, about 14.5 percent of the total. Most of California’s nearly 400 hydropower plants are located in the eastern mountain ranges where large streams descend down a steep grade.
One big benefit of water power is that it does not burn a fuel. This benefit gives water power an advantage over most other energy resources in how it affects the environment. Because water power does not burn a fuel, it causes less pollution than many other kinds of energy. Another benefit of water power is that, like the other resources you are learning about in this lesson, it is a renewable resource. We use energy from the water’s movement, but we are not using up the water itself. Water keeps flowing into our rivers and lakes, so wherever we can build plants to use it, water will be available as a source of energy. The energy of waves and tides can also be used to produce water power.
Water power does have its problems, though. When a large dam is built, this creates a reservoir, changing the ecosystem upstream. Large river ecosystems are inundated, killing all the plants and animals. The dams and turbines also change the downstream environment for fish and other living things. Dams also slow the release of silt, so that downstream deltas retreat and seaside cities become dangerously exposed to storms and rising sea levels. Tidal power stations may need to close off a narrow bay or estuary. Wave power applications have to be able to withstand coastal storms and the corrosion of seawater.

## Wind Power

As you learned earlier, the sun provides plenty of energy to the Earth. The energy from the sun also creates wind (Figure 5.9). Learning about what causes wind will help you understand that energy can move as heat, not just by radiation and conduction, but also by convection. Wind happens when the sun heats some parts of the Earth differently. For example, sunlight hits the equator much more directly than it hits the North and South Poles. Hot air rises and cooler air moves in, so when the air near the equator is heated much more than the air near the poles, the air begins to move carrying heat through the air in a process called convection. This movement of air is wind.
Wind power uses moving air as a source of energy. Some examples of wind power have been around for a long time. Windmills have been used to grind grain and pump water for hundreds of years. Ships with sails have depended on wind for even longer. Wind can be used to generate electricity, too. Like the moving water that creates water power, the moving air can make a turbine spin to make electricity.
To help you understand how moving air can be used to make electricity, you could think back to what you have learned about energy of motion, called kinetic energy. Any form of matter that is moving has kinetic energy. Even though you cannot see air, it is matter, because it takes up space and has mass. So, when wind makes the air move, this air has kinetic energy. When the moving air hits the blades of a turbine, it makes those blades move, and the turbine spins. The spinning of the turbine creates electricity.
Wind power has many advantages. It is clean energy, meaning that it does not cause pollution or release carbon dioxide. Also, wind is plentiful almost everywhere. One problem with wind energy is that the wind does not blow all of the time. One solution is to find efficient ways to store energy for later use. Until then, another energy source needs to be available when the wind is not blowing. Lastly, windmills are expensive and wear out quickly. For the amount of energy they generate, windmills are more expensive than some other forms of renewable energy.
California was an early adopter of wind power. Windmills are found in mountain passes, especially where cooler Pacific ocean air is sucked across the passes and into the warmer inland valleys. Large fields of windmills can be seen at Altamont pass in the eastern San Francisco Bay Area, San Gorgonio Pass east of Los Angeles, and Tehachapi Pass at the southern end of the San Joaquin Valley.

## Biomass

Another renewable source of energy is biomass. Biomass is the material that comes from plants and animals that were recently living. Biomass also includes the waste that plants and animals produce. People can use biomass directly for heating. For example, many people burn wood in fireplaces or in wood-burning stoves.
Besides burning biomass directly for heating, people can process biomass to make fuel. This processing makes what is called biofuel. Biofuel is a fairly new type of energy that is becoming more popular. People can use fuels from biomass in many of the same ways that they use fossil fuels. For example, some mechanics have made changes to car, truck, and bus engines to allow them to use a fuel called biodiesel. Other engines can run on pure vegetable oil or even recycled vegetable oil.
If we use fuels made from biomass, we can cut down on the amount of fossil fuel that we use. Because living plants take carbon dioxide out of the air, growing plants for biofuel can mean that we will put less of this gas into the air overall. This could help us do something about the problem of global warming.

## Geothermal Energy

Geothermal energy is a source of energy that comes from heat deep below the surface of the Earth. This heat produces hot water and steam from rocks that are heated by magma. Power plants that use this type of energy get to the heat by drilling wells into these rocks. The hot water or steam comes up through these wells. Then, the hot water or steam makes a turbine spin to make electricity. Because the hot water or steam can be used directly to make a turbine spin, geothermal energy is a resource that can be used without processing. The fact that it does not need to be processed makes geothermal energy different from most other energy resources. Geothermal energy is clean and safe. It is renewable, too, because the power plant can pump the hot water back into the underground pool. There, the water can pick up heat to make more steam.
This source of energy is an excellent resource in some parts of the world. For example, Iceland is a country that gets about one fourth of its electricity from geothermal sources. In the United States, California leads all states in producing geothermal energy. Geothermal energy in California is concentrated in a few areas in the northern part of the state. The largest geothermal power plant in the state is in the Geysers Geothermal Resource Area in Napa and Sonoma Counties. The source of heat is thought to be a large magma chamber lying beneath the area, a part of the Pacific Ring of Fire. Many parts of the world do not have underground sources of heat that are close enough to the surface for building geothermal power plants.

## Lesson Summary

* Solar energy, water power, wind power, biomass energy and geothermal energy are renewable energy sources.
* Solar energy can be used either by passively storing and holding the sun’s heat, converting it to electricity or concentrating it.
* There are many ways to use the energy of moving water including hydroelectric dams.
* Wind power uses the energy of moving air to turn turbines.
* Biomass energy uses renewable materials like wood or grains to produce energy.
* Geothermal energy uses heat from deep within the earth to heat homes or produce steam that turns turbines.

## Review Questions

* If you turn on the burner on a gas stove under a pan of cold water, energy moves from the burner to the pan of water. What is this energy called? How does this energy move?
* What are some ways that we can use solar power?
* If you burn wood in a fireplace, which type of energy resource are you using?
* Which form of energy is an important factor in making electricity from water power?
* When the air moves around as wind, it carries heat from warmer areas to cooler areas. What is this movement of heat called?
* Most of the energy that travels from the sun to the Earth arrives in the form of visible light. What is this movement of energy called?
* Explain how mirrors can be useful in some solar energy plants.
* Explain how wind power uses kinetic energy.

## Vocabulary
### conduction

    The process in which energy moves through matter as heat, moving from an area of higher temperature to an area of lower temperature.

### convection

    The movement of heat in an air current from a warmer space to a cooler space.

### radiation

    The movement of energy through empty space.

## Points to Consider

* What areas do you think would be best for using solar energy?
* What causes the high temperatures deep inside the Earth that make geothermal energy possible?
* Do you think your town or city could use wind or water power?
← Nonrenewable Energy Resources · Plate Tectonics →