EUES - Renewable Energy Sources (Lesson)

Renewable Energy Sources

What Are Renewable Resources?

Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. In addition to the wind, renewable energy resources include sunlight, moving water, biomass, and geothermal energy. All of these resources are freely available and won't run out. Most of them also have the advantage of producing little if any pollution or carbon dioxide, which contributes to global climate change. Nonetheless, these energy resources are used far less than nonrenewable energy resources, especially fossil fuels. 

Sunlight

The sunlight that reaches Earth is the planet's most important source of energy. The energy in sunlight, called solar energy, is electromagnetic energy. This is a form of energy that travels through space in electric and magnetic waves. Solar energy can be used to heat homes and produce electricity in solar cells. Sunny areas receive plenty of sunlight to generate electricity, but solar energy may not be practical in areas that are often cloudy.

Society's use of solar power on a larger scale is just starting to increase. Scientists and engineers have very active, ongoing research into new ways to harness energy from the Sun more efficiently. Because of the tremendous amount of incoming sunlight, solar power is being developed in the United States in southeastern California, Nevada, and Arizona.

Photovoltaic Panel Array

 

Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver. A liquid, such as oil or water, flows through this receiver and is heated to a high temperature by the focused sunlight. The heated liquid transfers its heat to a nearby object that is at a lower temperature through a process called conduction. The energy conducted by the heated liquid is used to make electricity.

Consequences of Solar Power Use

Solar energy has many benefits. It is extremely abundant, widespread, and will never run out. But there are problems with the widespread use of solar power.

• Sunlight must be present. Solar power is not useful in locations that are often cloudy or dark. However, storage technology is being developed.
• The technology needed for solar power is still expensive. An increase in interested customers will provide incentives for companies to research and develop new technologies and to figure out how to mass-produce existing technologies.
• Solar panels require a lot of space. Fortunately, solar panels can be placed on any rooftop to supply at least some of the power required for a home or business.

Other Solar Powered Technologies

 

Diagram explaining how solar water heating works

• Cold water enters through an inlet
• Into an insulated storage tank
• From there it flows through a panel
• Which absorbs solar radiation

 

The solar energy is absorbed as heat and the hot water re-enters the tank where it exchanges heat with the rest of the water through convection or a heat exchanger. Hot water exits the tank at the top where it can be used (E). The temperature at the top of the tank (F+) is higher than that at the bottom (G-) because of the reduced specific mass of warmer water.

Wind Energy

The wind is moving air, so it has mechanical energy that can do work. People have been using wind for energy for thousands of years. The old-fashioned windmill is one way that wind energy can be used. The wind turbines in the image above are a much newer way of using wind energy. They change the kinetic energy of the wind to electrical energy. However, only certain areas of the world get enough steady wind to produce much electricity. Many people also think that wind turbines are noisy, dangerous to birds, and unattractive in the landscape. 

Consequences of Wind Power

Wind power has many advantages. It does not burn, so it does not release pollution or carbon dioxide. Also, the wind is plentiful in many places. Wind, however, does not blow all of the time, even though power is needed all of the time. Just as with solar power, engineers are working on technologies that can store wind power for later use.

Windmills are expensive and wear out quickly. A lot of windmills are needed to power a region, so nearby residents may complain about the loss of a nice view if a wind farm is built. Coastlines typically receive a lot of wind, but wind farms built near beaches may cause unhappiness for local residents and tourists.

The Cape Wind project off of Cape Cod, Massachusetts has been approved but is generating much controversy. Opponents are in favor of green power but not at that location. Proponents say that clean energy is needed and the project would supply 75% of the electricity needed for Cape Cod and nearby islands.

California was an early adopter of wind power. Windmills are found in mountain passes, where the cooler Pacific Ocean air is sucked through on its way to 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.

Moving Water

The mechanical energy of rapidly flowing water can turn a turbine and generate electricity. Electricity produced in this way is called hydroelectric power. The water may flow over a waterfall or through a dam. You can see a dam pictured here. A drawback of dams is that they flood land upstream from the dam and reduce water flow downstream from the dam, and this can destroy ecosystems.

Water covers 70% of the planet's surface, and water power (hydroelectric power) is the most widely used form of renewable energy in the world. Hydroelectric power from streams provides almost one-fifth of the world's electricity.

Hydroelectric Power

Remember that potential energy is the energy of an object waiting to fall. Water held behind a dam has a lot of potential energy.

In a hydroelectric plant, a dam across a riverbed holds a stream to create a reservoir. Instead of flowing down its normal channel, the water is allowed to flow into a large turbine. As the water moves, it has kinetic energy, which makes the turbine spin. The turbine is connected to a generator, which makes electricity.

Hoover Dam Generators

 

Consequences of Water Power Use

The major benefit of hydropower is that it generates power without releasing any pollution. Hydropower is also a renewable resource since the stream will keep on flowing. However, there are a limited number of suitable dam sites. Hydropower also has environmental problems. When a large dam disrupts a river's flow, it changes the ecosystem upstream. As the land is flooded by rising water, plants and animals are displaced or killed. Many beautiful landscapes, villages, and archeological sites have been drowned by the water in a reservoir.

The dam and turbines also change the downstream environment for fish and other living things. Dams slow the release of silt so that downstream deltas retreat and seaside cities become dangerously exposed to storms and rising sea levels. The picture to the right shows a salmon, or fish, ladder. These ladders provide a route for the fish to travel upstream, around dams and other man-made obstructions.

Ocean Water Power

The energy of waves and tides can be used to produce water power. 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. Because of the many problems with them, tide and wave power plants are not very common. Although not yet widely used, many believe tidal power has more potential than wind or solar power for meeting alternative energy needs.

Geothermal Energy

The heat that is used for geothermal power may come to the surface naturally as hot springs or geysers, like The Geysers in northern California. Where water does not naturally come to the surface, engineers may pump cool water into the ground. The water is heated by the hot rock and then pumped back to the surface for use. The hot water or steam from a geothermal well spins a turbine to make electricity.

Geothermal energy is clean and safe. The energy source is renewable since hot rock is found everywhere within Earth, although in many parts of the world the hot rock is not close enough to the surface for building geothermal power plants. In some areas, geothermal power is common.

In the United States, California is a leader in producing geothermal energy. 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.

Biomass

For many people in the world, wood is their main energy resource. They burn it to stay warm as well as to cook their food. The photo at the right shows Iraqi women who are making flatbread with an outdoor clay stove that uses wood as fuel. Other energy resources, such as oil or gas, are simply not available to them or are far too expensive for most people to use. However, if you live in the U.S. or another of the richer nations of the world, you probably depend almost totally on these more expensive energy resources, especially oil.

The stored chemical energy in organic matter or wastes is called biomass energy. The organic matter may be trees or other plants, or it may be wastes from homes and industries. When biomass is burned, it produces thermal energy that can be used for heating homes, cooking, or generating electricity. Biomass—especially wood—is an important energy source in the poorer nations where most people can't afford fossil fuels. However, burning biomass releases air pollution and contributes to global climate change. Biomass can be used to make ethanol, a fuel that is added to gasoline. Although ethanol releases less pollution than gasoline, large areas of land are needed to grow the plants needed to make it. This reduces the amount of land available for food production.

Consequences of Biomass Use

In many instances, the amount of energy, fertilizer, and land needed to produce the crops used to make biofuels mean that they often produce very little more energy than they consume. The fertilizers and pesticides used to grow the crops run off and become damaging pollutants in nearby water bodies or in the oceans.

To generate biomass energy, break down the cell walls of plants to release the sugars and then ferment those sugars to create fuel. Corn is a very inefficient source; scientists are looking for much better sources of biomass energy. Below is a photo of the Stevens Croft Biomass Plant. This plant opened in 2008, the largest biomass plant in Scotland with an output of 44MW.

 

 

Other Sources of Biomass

Learn more about these alternatives by clicking on the links below.

• Omega System Links to an external site.
• Ethanol Links to an external site.
• Municipal Solid Waste (MSW) Energy Generation Links to an external site.

 

Ethanol Production Plant

 

 

 

RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.