Caches of natural volcanic activity in remote areas of the state make California the largest producer of geothermal energy – more than one half of the world’s supply. And since the 1980s, Southern California Edison has been capturing heat from this abundant renewable resource and converting it to electricity.

Geothermal energy is derived as water flows underground and is heated by magma, a very hot liquid rock formation on the mantle of the earth. Hot water is pushed upward through cracks in the earth’s crust and rises to the surface – creating geysers and hot springs.

A geothermal power plant uses the hot water or steam captured in wells to produce electricity.  These plants operate around the clock, due to the constant temperature maintained at certain levels below the earth’s surface – making geothermal a very viable and reliable source of energy.

In 2007 alone, SCE purchased $579 million worth of geothermal power, which made up about eight percent of the electricity delivered to you. We now hold 19 geothermal contracts with the capacity of 955 megawatts – enough to power half a million homes with this clean green energy.

HOW IT WORKS - Geothermal Energy

Steam, heat or hot water from reservoirs provides the force that spins turbines which turn generators to produces electricity. The water is then returned to sustain the reservoir where it is reheated, and used again, .
Geothermal plant construction depends on the temperatures and pressures of the geothermal fluid (brine) at the site:

1. Dry Power Plant. A "dry'" steam reservoir produces steam but very little water. The steam is piped directly into a "dry" steam power plant to provide the force to spin the turbine generator. The largest dry steam field in the world is The Geysers, about 90 miles north of San Francisco. Production of electricity started at The Geysers in 1960, at what has become the most successful alternative energy project in history.
   
2. Flash Power Plant. A geothermal reservoir that produces mostly hot water is called a "hot water reservoir" and is used in a "flash" power plant. Water ranging in temperature from 300 - 700 degrees F is brought up to the surface through production wells where, upon being released from the pressure of the deep reservoir, some of the water flashes into steam in a 'separator.' The steam then powers the turbines.
   
3. Binary Power Plant. A reservoir with temperatures between 250 - 360 degrees F is not hot enough to flash enough steam to be practical but can still be used to produce electricity in a "binary" power plant. In a binary system the geothermal water is passed through a heat exchanger, where its heat is transferred into a second (binary) liquid, such as isopentane, that boils at a lower temperature than water. When heated, the binary liquid flashes to vapor, which, like steam, expands across and spins the turbine blades. The vapor is then recondensed to a liquid and is reused repeatedly. In this closed loop cycle, there are no emissions to the air.

BENEFITS OF GEOPOWER

• Clean Energy. Geothermal power plants, like wind and solar power plants, do not have to burn fossil fuels or natural gas to generate steam to turn the turbines. This helps reduce harmful emissions in the atmosphere. There is no smoky air around geothermal power plants and offering net benefits on forestry, crops, cattle and local wildlife. There can be however, some air emissions from these plants that must be considered when comparing to other alternatives. 
  
• Easy on the land. The land area required for geothermal power plants is smaller per megawatt than for almost every other type of power plant. Geothermal installations don't require damming of rivers or harvesting of forests, and there are no mine shafts, tunnels, open pits, waste heaps or oil spills. Some geothermal resources include traces of hazardous chemicals that must be disposed of properly.
  
• Reliable. Geothermal power plants are designed to run 24 hours a day, year long. A geothermal power plant is positioned right on top of its fuel source. It is resistant to interruptions of power generation due to weather, natural disasters or transportation.
  
• Flexible. Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity.
  
• Economical. Money does not have to be spent to import other fuels. Geothermal energy is derived on location and can be distributed locally.
  
• Helps Developing Countries Grow. Geothermal projects can offer all of the above benefits to help developing countries grow without pollution. And installations in remote locations can raise the standard of living and quality of life.

OTHER USES OF GEOTHERMAL ENERGY?

• Geothermal waters ranging from 50 degrees F to over 300 degrees F, are used in various ways in different parts of the earth, mainly for heating and cooling needs.
  
• Medicinally to soothe aching muscles in hot springs, and health spas.
  
• For agriculture and industry to help grow flowers, vegetables, and other crops. Pipes carrying geothermal water have been installed under soil, where flowers or vegetables are growing to ensures that the ground does not freeze, providing a longer growing season and overall faster growth of agricultural products that are not protected by the shelter and warmth of a greenhouse. Also to shorten the time needed for growing fish, shrimp, abalone and alligators to maturity; to pasteurize milk, to dry onions, to dry lumber, and to wash wool.
  
• Space heating of individual buildings and of entire districts. Geothermal district heating systems pump geothermal water through a heat exchanger, where it transfers its heat to clean city water that is piped to buildings in the district. There, a second heat exchanger transfers the heat to the building's heating system. The geothermal water is injected down a well back into the reservoir to be heated and used again.
  
• In the U.S., geothermal water is also piped under roads and sidewalks to keep them from icing over in freezing weather. The cost of using any other method to keep hot water running continuously through cold pipes would be prohibitive.

Learn More at http://geothermal.marin.org/pwrheat.html