Fossil fuel supplies are limited since they aren’t a(n) renewable energy source. We need to conserve energy supplies so they’re not exhausted. One alternative energy source is the waterwheel. It can be used in a hydroelectric plant, where water spins a(n) generator. Moving air or wind also can be harnessed for electricity. The steam from water heated by geothermal energy produces electricity. Solar cells convert sunlight into electric energy. Another form of energy comes from biomass, or plant and animal wastes.