'Geothermal energy, or heat generated from the earth, is largely non-polluting, and is renewable and reliable," says Ashley Winters and John Parke.

In Stephen Leeb's The Complete Investor, the contributing editors look at a trio of diverse plays on geothermal energy:  Chevron (NYSE: CVX), Calpine (NYSE: CPN), and Ormat Technologies (NYSE: ORA). 

"Throughout the globe, heat is continually produced in a layer far below the earth’s crust. Large power plants can capture and use this steam to provide electricity on a fairly large scale.

"In Iceland, by some estimates, 50% of all energy needs are met through an alternative energy source that has been known for a long time, 

"Geothermal is used in many other places as well. The largest system in operation is in California just north of San Francisco, in an area known as the Geysers.

"Efforts are also underway to use geothermal heat via 'hot dry rock' technology. Rocks are broken up by pumping water through them at high pressure; water is then pumped through the broken rocks so that it can be heated by the earth’s energy.

"Finally, geothermal energy also can be tapped through ground-source heat pumps, effective in heating and cooling individual buildings. This approach takes advantage of the fact that just five to 10 feet below the ground there is a constant temperature of around 50 degrees F.

"Right now the U.S. has nearly 3,000 megawatts (MW) of installed geothermal energy capacity and is the global leader in total geothermal electric power production. 

"Over the next five to 10 years, capacity should grow by at least 20% a year.