Resources

Solar energy diagram

Biofuels

In the United States, ethanol is the primary biofuel in use. U.S. ethanol production now makes up about 3 percent of U.S. annual gasoline usage. In calendar 2005, the United States consumed 139.9 billion gallons of gasoline and 4.04 billion gallons of ethanol. By comparison, biodiesel consumption made up about 75 million gallons, out of 38.3 billion gallons of the diesel consumed for transportation.

Chart and photos of biofuel inputs

To further encourage U.S. biofuel consumption, the Energy Policy Act of 2005 for the first time established a federal mandate — called the Renewable Fuel Standard—to require a certain amount of biofuel consumption. Under the Act, Congress mandated a 4-billion gallon total for national biofuel consumption in 2006, with an increase to 7.5 billion gallons by 2012.

Hydroelectric Power

On Earth, water is neither created nor destroyed, but is constantly moved around. Water evaporates from the oceans, rivers and lakes and is stored by the atmosphere. Under certain weather conditions water vapor in air condenses to form clouds, eventually precipitating out as rain, snow, sleet and hail. This precipitation collects into streams and rivers, and flows back to the sea. This is called the water cycle.

All this movement provides an enormous opportunity to create useful energy. Hydroelectric power (HEP) uses the force of moving water to create electricity. However, HEP stations often require large dams, which can disrupt ecosystems and displace people.

Water is currently the leading renewable energy source used by electric utilities to generate electric power. Hydroelectric plants operate where suitable waterways are available; many of the best of these sites have already been developed. Generating electricity using water has several advantages: cheap power, little air pollution in comparison with fossil fuel plants, and limited thermal pollution compared with nuclear plants. Like other energy sources, use of water for generation has limitations, including environmental impacts caused by damming rivers and streams, affecting the habitats of the local plant, fish, and animal life.

Geothermal Energy

As of August 2008, almost 4,000 MW of new geothermal power plant capacity was under development in the U.S. (including projects in the initial development phases). Those states with projects currently under consideration or development are: Alaska, Arizona, California, Colorado, Florida, Hawaii, Idaho, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Combined, these states have approximately 103 projects in development ranging, from initial to advanced stages. (6)

Direct uses applications of geothermal energy occur today in 26 states—almost as many states as produce coal. (7) New direct use projects are encouraged by the provisions of the Geothermal Steam Act Amendments passed by Congress in 2005. There is interest in new direct use projects in numerous states and on various Indian reservations within several states.

Geothermal heat pump installations have been growing at an annual rate of 15 percent, with more than 600,000 units installed in the U.S. by the end of 2005. Every year in the U.S., 50,000 to 60,000 new units are installed—the largest growth in the world for geothermal heat pumps. (8)

Tidal Power

One of the Earth’s great renewable energy sources is the energy found in ocean waves. Let’s look at this further.

If you have ever been to the ocean, you were probably fascinated by the phenomena of the waves crashing against the shorelines as the tides came in. The ocean’s tides are the product of gravitational pull of the sun and the moon, as well as the Earth’s rotation. It causes ocean waters to be raised and lowered from time to time. The tides have cycles of twelve and one-half hours, twice a day, and are easily predictable.

The use of tidal power is seen as early as the twelfth century where tidal mills used the force of the tides to grind grain and corn. The eighteenth century brought competition from windmills and waterwheels. Tidal mills pretty much became extinct with the invention of cheap steam engines. In 1967, France became the first to be able to put tidal wave power to work on a large scale to produce electricity.

The generation of electricity from tidal waves is similar to that of hydroelectric power generation. Bigger dams, known as barrages, are built on the bottom of a tidal basin. Gates on the barrage allow the tidal basin to fill during incoming high tides. Likewise, the basin will empty through a turbine during the outgoing tide. This turns an electric generator for the production of electricity. There are also systems that generate electricity from incoming and outgoing tides. This system can have a negative effect on plants and animals in the area.

Tidal fences are also used to generate electricity. Vertical axis turbines are mounted on fences. Passing water is forced through the turbines. Ideal locations for these are channels between two landmasses. Tidal fences are cheaper than tidal barrages and cause less of an environmental impact on large marine life.

Tidal turbines are a new technology used for tidal energy. They are similar to wind turbines and are arranged underwater in rows. They work best in areas with strong tides. Although they are heavier and costlier to build, they also are capable of capturing more energy. Off all the tidal power technologies, they are also the least environmentally damaging, because they do not interfere with migration paths.

In order for tidal power to work successfully it must be a tide difference of at least sixteen feet. Unfortunately there are only a few places where this occurs. This means tidal power plants cannot be constructed just anywhere. There are only a handful of sites on Earth with this type of tidal range. At present, France is the only country that has been successful in using tidal power. It is hoped developments in technology, through research, will be made to allow better use of, what is now, wasted energy. The future of tidal energy seems hopeful, with great potential for better use in the future quest to find a replacement for fossil fuels.