"Every day we need more and more energy to run our factories, airplanes, cars, ships, computers and other modern marvels.  Some of the energy we now consume comes from burning petroleum that is derived from crude oil. Other major energy sources include coal, natural gas and uranium.  Unfortunately, using these materials leads to numerous environmental problems.  In addition, none of these energy sources is renewable. In other words, their supplies are limited and become harder to get every day."