Renewable resources are defined as natural resources that can be replaced naturally over a relatively short amount of time. Therefore, fossil fuels do not qualify; while oil and coal will eventually renew themselves, the geologic processes required to convert dead biomass into fossil fuels require hundreds of millions of years.
Renewable resources must also be sustainable and must have a minimal impact on the environment. Also known as “green resources,” renewables include solar power, wind, geothermal, biomass and even ocean tides. Arguably, hydropower is renewable; however, the dams along these rivers often have a negative impact on the environment, particularly on marine life forms that depend on said rivers.
Currently, solar is at the top of renewable resources. This form of energy is growing at a rate of 50% per year, and small wonder; the amount of potential energy receives from the sun every year exceeds the amount used by civilization by some 10,000%. At the time of this writing, the most promising of solar energy technologies involves multijunction solar cells, which unlike earlier solar cells (such as those that have long powered hand-held calculators), are able to use the full spectrum of lightwaves, including non-visible infrared and ultraviolet. Some companies and scientists are also researching a form of artificial photosynthesis, the chemical process by which plants and some types of bacteria convert light into food; such solar systems could produce liquid and gaseous fuels to replace petroleum and coal products.
Few people realize today that Rudolf Diesel’s internal combustion engine was originally designed to run on peanut oil. Today, diesel fuel is being produced from a variety of renewable resources, primarily used food-grade vegetable oils. Alcohol from sugar cane and switchgrass also represent renewable resources because these crops grow relatively fast and ‘ in the case of switchgrass ‘ can be grown on marginal land unsuitable for food production.
Another interesting fact that few people realize is that the earth itself radiates nearly as much energy as it receives from the sun. Geothermal is not available everywhere, but in geologically active regions such as the Pacific Rim and the Mediterranean, energy from the decay of naturally-occurring elements deep under the ground are being used to generate electricity and heat.