SOLAR - WIND - WAVE - TIDE - HYDROPOWER - GEOTHERMAL - NUCLEAR - BIOFUELS - BIOMASS - ENERGY STORAGE
Imagine the effect of keeping an additional $500 Billion in the U.S. economy every year! This is the effect of renewable energy and why it will be so important to our future. Renewable energy is the harnessing of natural resources--sunlight, wind, tide, all infinitely renewable--in order to (re)power applications that are currently using non-renewable resources--namely, oil and coal. Additionally, plants grow and produce biomass--also renewable--which can then be utilized directly as fuel or to produce biofuels.
Because renewable is, by its very nature, a "periodic" phenomenon, energy storage is crucial. The sun is at its highest, and thus is at its most potent, during the middle of the day; this in contrast to wind, for instance, which often peaks at night (geothermal is one naturally recurring infinitely renewable resource which is always constant). Rechargeable batteries can soak up excess energy from any and all natural resources during peak hours, and then discharge said energy accordingly as needed (during a cloudy day, for example--or a windless night). Hence: infinitely renewable energy available all the time.