Renewable is energy generated from natural resources the are naturally replenished in a short period of time. The main renewable sources are:

•  Biomass is organic material made from plants and animals, such as wood, crops (ethanol), municipal solid waste, landfill and biogas, and biodiesel (made from vegetable oils, animal fats, or greases). Biomass contains stored energy from the sun. Plants absorb the sun's energy through photosynthesis. The chemical energy in plants gets passed on to animals and people that consume them. When burned, the chemical energy in biomass is released as heat. Biomass fuels provide about 3 percent of the energy used in the United States.
   
• Hydropower is derived by directing, harnessing, or channeling moving water. The amount of available energy in moving water is determined by its flow or fall. The water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released when the demand for electricity is high. Meanwhile, the reservoirs or lakes are used for boating and fishing, and often the rivers beyond the dams provide opportunities for whitewater rafting and kayaking.
   
• Geothermal energy is heat from within the earth. The steam and hot water produced inside the earth is used to heat buildings or generate electricity. People around the world use geothermal energy to heat their homes and to produce electricity by digging deep wells and pumping the heated underground water or steam to the surface. Or, make use of the stable temperatures near the surface of the earth to heat and cool buildings.
   
• Wind power is created by wind machines using blades to collect the wind’s kinetic energy. Windmills work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. With the new wind machines, there is still the problem of what to do when the wind isn’t blowing. At those times, other types of power plants must be used to make electricity.
   
• Solar energy is the sun’s rays (solar radiation) that reach the earth. Solar energy can be converted into other forms of energy, such as heat and electricity. Solar energy can be converted to thermal (or heat) energy and used to heat water (for use in homes, buildings, or swimming pools) and heat spaces (inside greenhouses, homes, and other buildings). Solar energy can be converted to electricity into either Solar Power Plants or Photovoltaic (or "solar cells" that change sunlight directly into electricity). Photovoltaic systems are often used in remote locations that are not connected to the electric grid. They are also used to power watches, calculators, and lighted road signs.

 1.) U.S. Environmental Protection Agency. Wastes - Resource Conservation - Reduce, Reuse, Recycle. http://www.epa.gov/osw/conserve/rrr/recycle.htm