Alternative sources of energy are derived from sources that do not use up natural resources and do not harm the environment. They are alternatives to fossil fuels, nuclear energy and large-scale hydroelectric power, which all are exhaustible energy sources that have varying degrees of harmful effects on the environment. Still, there are no alternative sources of energy that are as commercially viable as oil, which along with coal are the main types of fossil fuels.

The first of all the alternative sources of energy that usually comes to mind is solar energy, which is any of several different procedures used to harness energy that comes from the sun. The primary method used to convert sunlight into electricity is through the use of photovoltaic cells, which are arranged on solar panels in such a way that a maximum amount of sunlight is absorbed and turned into electricity. Currently, the biggest issue with solar power is the cost, since the solar cells and panels can be very expensive.

Another alternative energy source is wind energy, which uses large wind turbines to transform wind into power. Many of these turbines can be placed where wind is abundant, and these wind farms can be connected to a power grid to which they contribute electricity. A windmill can also be used to harness wind energy, but rather than turning the wind into electricity, a windmill converts the wind directly into mechanical motion to do work.

Some alternative sources of energy receive power from earthly sources, as in geothermal power, tidal power and biomass. Geothermal power is derived from heat sources within the earth, such as natural geysers, and converts this heat into electricity. The harnessing of power from waves in the ocean and other bodies of water on the planet is known as tidal power. Finally, biomass energy is obtained from organic material that comes from plants and animals, and is known more commonly as a renewable energy source since it creates a waste by-product. All of these alternative sources of energy must be researched heavily if any of them are ever going to replace fossil fuels as primary power sources throughout the world.