Proven Alternative Energy Sources Several kinds of renewable and clean sources of energy such as wind, solar, geothermal, hydro, biomass energy are now available. Each alternative source has its own characteristic importance depending upon geographical possibilities for its production. It will be most appropriate to delve deeper into each one of these sources. Wind Energy Wind energy is available mostly at the coastal regions where wind velocity is higher. Kinetic energy of the wind is tapped using wind turbines and converted into mechanical or electrical energy. Mechanical energy can be used to produce either electricity or can be used directly to run wind mill. For an efficient use of wind turbines, wind velocity of 11 meters per second or higher is desirable. Wind velocity mapping is necessary while selecting a site for installation of a wind turbine because higher wind speeds will provide higher kilowatts of electricity (Renewable energy sources in the United States, 2011). Solar Energy Solar radiation provides continuous flow of clean and renewable energy and in that sense Sun is the most potential alternative source of energy that can always be relied upon. Earth's existence is linked with Sun. Thus, here is the source of energy that can never get exhausted at least theoretically. Though technologies are rapidly advancing to tap this source of energy yet certain impediments such as cost and space do pose certain difficulties. The state of California leads in solar power installations in the US. World over, many countries particularly those with strong solar radiations have been investing heavily in solar photovoltaic cells to harness this source of energy (Renewable energy sources in the United States, 2011). Hydropower This is a clean and renewable alternative source of energy which can be banked upon. Almost 7 percent of the total electricity produced in the US comes from hydropower sources. The Colorado River and the Tennessee Valley are the potential sources of hydropower production (Renewable energy sources in the United States, 2011). Large and small dams are the places to install turbines where the potential energy of water is used to produce electricity. As per the World Bank report, hydropower currently meets almost 18 percent of the total world electricity needs. Hydropower is considered the most affordable renewable energy source among all available energy sources (Hydropower 2012). Geothermal Energy When Earth's heat is tapped to produce electricity, it is known as geothermal source of energy. Temperature inside our earth remains more or less constant throughout the year. This energy is tapped using various technologies such as heat pumps, direct-use systems, and deep reservoirs. The heat is recovered from water or steam and converted into electricity. Many residential and commercial buildings are heated using heat pumps. Utah, Hawaii, California, Nevada are some of the places where geothermal energy plants are in operations (Renewable energy sources in the United States, 2011). Biomass Power or Biopower Food crops, organic municipal wastes, grassy and woody plants and farm residues are used to produce electricity and that falls in this category. Plant sources are used as major feedstock to produce Biopower and because they are available everywhere, Biomass power can be produced in any part of the world.