One of the greatest natural sources of energy available on Earth is the sun. Solar energy can be converted directly into electrical power without the need for mechanical generators through the use of photoelectric cells. Alternatively, large solar collectors known as heliostats can be used to focus solar energy into a water boiler, generating steam to run conventional electrical turbines. Unfortunately, at our current level of technology, both of these systems are prohibitively expensive to construct. However, because of the dwindling supply of fossil fuels and increasing concern over the pollution produced by conventional and nuclear power plants, scientists are constantly working on a viable way to harness the clean and endless supply of energy provided by our sun.