Geothermal Heat Pumps
A geothermal heat pump is an electric heat pump that draws heat from or discharges heat to the ground or ground water, instead of air. This works because the ground temperature which is 10-12 feet below the earths's surface stays relatively constant at 55 degrees Fahrenheit. A turbine is driven either from hot water or by natural steam that derives its energy from the Earth's heat. An "open loop" geothermal heat pump uses heat found in rocks or fluids at various depths beneath the surface of the earth, and receives/discharges fluids from the earth. The fluids are extracted by drilling and/or pumping. A "closed loop" geothermal heat pump pipes a fluid in a closed piping system underground, which receives heat from or discharges heat to the Earth.
Hydroelectric
Water is currently the leading renewable energy source used by electric utilities to generate electric power. Hydroelectric plants operate where suitable waterways are available; many of the best of these sites have already been developed. Generating electricity using water has several advantages. The major advantage is that water is a source of cheap power. In addition, because there is no fuel combustion, there is little air pollution in comparison with fossil fuel plants and limited thermal pollution compared with nuclear plants. Like other energy sources, the use of water for generation has limitations, including environmental impacts caused by damming rivers and streams, which affects the habitats of the local plant, fish, and animal life.
Solar Thermal
Solar thermal devices use direct heat from the sun, concentrating it in some manner to produce heat at useful temperatures. The modern solar industry began with the oil embargo of 1973-1974 and was strengthened with the second embargo in 1979. The growth of the solar industry during this period of fuel shortages and high prices (1974-1984) soared from 45 solar collector manufacturing firms to 225 firms. The solar market was helped during this period by government assistance, both Federal and State. Currently, solar thermal devices do everything from heating swimming pools to creating steam for electricity generation.
Solar Photovoltaic
Photovoltaic devices use semi conducting materials to convert sunlight directly into electricity. Solar radiation, which is nearly constant outside the Earth's atmosphere, varies with changing atmospheric conditions (clouds and dust) and the changing position of the Earth relative to the sun. Nevertheless, almost all U.S. regions have useful solar resources that can be accessed.
Wind
Winds are
created by uneven heating of the atmosphere by the sun, irregularities of the
Earth's surface, and the rotation of the Earth. As a result, winds are strongly
influenced and modified by local terrain, bodies of water, weather patterns,
vegetative cover, and other factors. The wind flow, or motion of energy when
harvested by wind turbines, can be used to generate electricity. Wind-based
electricity generating capacity has increased markedly in the United States
since 1970, although it remains a small faction of total electric
capacity.
Wind energy is the kinetic energy associated with the movement of atmospheric air. It has been used for hundreds of years for sailing, grinding grain, and for irrigation. Wind energy systems convert this kinetic energy to more useful forms of power. Wind energy systems for irrigation and milling have been in use since ancient times and since the beginning of the 20th century it is being used to generate electric power. Windmills for water pumping have been installed in many countries particularly in the rural areas.
