Concerns about the environment and climate change have led to policies aimed at promoting alternative energy to replace traditional coal, oil, gas and nuclear energy sources. The term alternative energy refers to some different types of energy technologies.

Renewable energy

Alternative energy has traditionally referred to renewable energy sources such as solar, wind, small hydropower, geothermal and biomass. Renewable energy sources are not permanently depleted like fossil fuel energy sources.

Environmental impacts

Alternative energy sources release significantly less air pollution and greenhouse gases than conventional fossil fuel sources, do not cause severe land degradation like coal mining, and do not produce any hazardous waste like nuclear energy.

Variations

Under the Bush administration, the term alternative energy was expanded to include ethanol, methanol, biodiesel, and coal-to-liquids. Some definitions also include hydrogen fuel.

Controversy

The environmental benefits of some of these other fuels that have been included in the definition are less clear. For example, ethanol and methanol derived from fossil fuels are not renewable.

Conservation

Energy conservation, efficiency, and use of waste heat can also be considered forms of alternative energy, even though they are not sources of energy per se, because they provide for the end use and thus reduce the need for generation with traditional energy sources.

Source:

Encyclopedia Britannica Online: Renewable Enerby

Grist: Coal Is Hardly Renewable