Renewable energy is generated from resources such as the sun, wind, rain, tides and geothermal heat which are naturally replenished.
"Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources."
In 2006 13% of renewable energy came from bio resources such as burning wood. Water power was next at about 3%. Solar energy for heating or water heating was about 1.3%. Geothermal wind power, solar power, and waven energy together provided less than 1% of the energy production.
Wind power can be used to drive turbines. Wind turbines range from around 600 kW to 5 MW of power rating. The output of a turbine is a function of the cube of the wind speed, so the faster the wind speed, the power output increases drastically. Since wind speed varies the total output of a wind turnbine farm is only a fraction of the potential. Normally in the 20-40% range of total possible capacity depending on location. Total world wide capacity is about forty times current world wide energy demand. Wind poweris renewable and produces no carbon dioxide or methane.
Water energy can be harnessed and used. Since water is much denser than air, even a slow flowing stream of water can yield considerable energy. Some forms of water power are: Hydroelectric energy via large-scale hydroelectric dams, Micro hydro, Damless hydro via energy derived from rivers without using a dam and Ocean energy.
Solar energy is energy that is collected from sunlight. Solar power can be used in many ways: turbines which are turned by rising hot air in a Solar updraft tower, solar powered satellites generating eletricity in obit around the earth, solar cells converting sunlight directly into electricity, and solar-thermal panels used to heat water or air for hot water and heating.
Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Usually biomass refers to plant matter grown to generate electricity or produce biofuel such as biodiesel and ethanol. Industrial biomass can be grown from plants such as miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane, and a variety of trees.
Geothermal is energy obtained by tapping the heat of the earth. It is expensive to build stations to retrieve the power but operating costs result in low energy costs. Geothermal energy is closer to the surface in some areas than in others. Where hot underground steam or water can be brought to the surface it can be used to generate electricity.