Renewable resources are those that are replaced naturally at a rate that is greater than or equal to human consumption. These resources are generally referred to when discussing energy sources. Wind, solar, hydropower and geothermal energy are examples of renewable sources. The increased use of renewable energies is important as researchers look for alternatives to fossil fuels, which some suggest may be closer to running out than people think.
Types
Five major types of renewable energies are in use. Wind power is the conversion of airflow by wind turbines into usable energy. Hydropower is the conversion of water flow, usually at dams, into usable energy. Similarly, geothermal energy is captured from Earth's internal heat, and solar energy is captured from the sun's light and radiation for usable energy. Biomass is the use and conversion of the energy contained within plants that perform photosynthesis.
Benefits
Renewable energy is beneficial for two key reasons. One, it is self-sustaining, meaning that the rate at which people use it does not exceed the rate at which it can replace itself naturally. Two, it is cleaner and less harmful to the environment than the fossil fuels in use today, which emit greenhouse gases when consumed.
Considerations
When considering the types of renewable energy to pursue, availability is a concern. Geothermal energy for example, has been historically limited to areas where Earth's inner heat approaches the surface, generally along tectonic plate boundaries. Hydropower on the other hand, is readily available, because even a relatively small body of moving water produces decent amounts of energy.
Potential
Although use of renewable energies has increased greatly in the 21st century, the true potential of these sources has yet to be realized. In 2002, the National Renewable Energy Laboratory released a report that found that at the time, wind power could produce 85 percent of the power needed in the western U.S. states, and solar power could produce twice the amount of power used in the western U.S. in 2001.
Future
Cellulosic ethanol is a fuel produced from grasses, wood and nonedible plant material that is being further pursued for use in vehicles. According to a fall 2007 report by Environment California, cellulose ethanol emits 80 percent less global warming pollution than gasoline. Greater use of the energy in ocean waves is also a possibility in the future.
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