There are three main types of feasible energy generation from geothermal sources. They include Hydrothermal, Geopressured, and Hot Dry Rock.

1. Hydrothermal generates electricity from hot water and steam that is formed in the earth: hot water (180 to 250 degrees Celsius) is extracted from underground reservoirs to the surface, where it is flashed to the steam point. The steam is then processed through a turbine.
   

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3. Geopressured energy is earth-captured, high-pressured hot water that contains methane. Energy can be produced from the hot water that’s flashed into steam, in the process converting high pressure into hydraulic energy and burning methane.
   

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5. Hot Dry Rock (HDR) or Enhanced Geothermal Energy (EGS) utilizes the earth’s heat to generate electricity. When drilling into the earth, a minimum of two drill sites are used. One is used to pump water in through an injection well. The other is used to extract the water that then turns to steam upon reaching high-temperature rocks through the production well. The steam is processed through a turbine.
   

The history of generating electricity from geothermal sources began in 1904 in Lardello, Italy. By 1913, the world’s first 250kW power station went live. During the 1930s, it was expanded, reaching 350MW in the 1970s.

In the US, the first hydrothermal facility was established in 1921 at The Geysers in Northern California. Despite this, geothermal energy took another forty years to become a reality: in 1960, PG&E opened up the first 11MW geothermal plant at The Geysers. The facility was operational through the early 1990s.

In the 1980’s the Northern California Power Agency (NCPA) began operating the country’s largest geothermal power plants at the Geysers Geothermal Field. Located 75 miles north of San Francisco, CA, dry superheated steam is delivered to two power plants each housing two 55MW geothermal turbine generators. The first plant went into operation in 1983 and was followed by the second in 1985. Both plants are supported by more than 65 production wells and 8 miles of pipeline.

US Geothermal Electricity Consumption in 2005: 14,690 GWh

Global Geothermal Energy Capacity in 2005: 9.3 GW

Global Geothermal Energy Capacity in 2006: 9.5 GW

US Geothermal Capacity in 2005: 2.56 GW

Philippines Geothermal Capacity in 2005: 1.93 GW

Mexico Geothermal Capacity in 2005: 0.95 GW

Indonesia Geothermal Capacity in 2005: 0.8 GW

Italy Geothermal Capacity in 2005: 0.79 GW

California Geysers Installed Capacity in 2005: 1.53 GW

California Geysers Operational Capacity in 2005: 0.93 GW

The benefits of geothermal are that it utilizes small footprint, has uninterrupted base-load power potential, does not require energy storage, and creates low emissions. The cost of an economical geothermal plant can be as low as $2800 per kW installed.

EGS--a new player on the on geothermal technology landscape--is seen as the geothermal energy of choice for the future. It was initially developed through funding by the Department of Energy (DOE) and researched by Los Alamos National Labs (LANL) in the 1970s and at the Fenton Hill site in New Mexico in the 1980s.

However, EGS comes with some high risks. Not only is the drilling procedure itself expensive, but drilling must be conducted at an estimated depth of 2 to 3 miles just to determine the viability of a site. There is no guarantee that heat mining will result in a viable underground heat source…nor is there a guarantee that it will provide sound possibilities for the heating and delivery of water or steam. Drilling costs are not cheap—a well can start at $4 million then vary depending on its depth. This added risk expense means that EGS ventures are difficult to instigate even though the technology has the greatest viable potential since thermal energy stored in the earth is present almost everywhere. (Access to this energy varies according to location and depth.)

Compared to other, less-consistent renewable technologies (i.e., wind and solar), geothermal can provide a base load energy 24/7.

NOTE ON NEW US GEOTHERMAL PLANT: In 2010, Western Geopower Corp. will open a new 35MW geothermal power plant 6 miles from the NCPA Geysers Geothermal Field. Per a 20-year arrangement of a $98-per-MWh set price, it’s estimated that this new facility will supply 265,000 MWh a year to NCPA.

NOTE ON PRE-DETERMINED GENERATION COSTS: According to the California Energy Commission (CEC), the generation costs are estimated to be $0.045 to $0.073 per kWh for geothermal. Industry developers peg these pre-determined generation costs as being $0.055 to $0.075 per kWh.

NOTE ON CALPINE: Calpine is an energy provider who owns 19 out of the 21 installed geothermal power production fields in The Geysers in Northern California. In all, Calpine has a geothermal production capacity of 725 MW.

UPDATE ON US GEOTHERMAL ENERGY: California produced 13,439GWh in 2007. By August of 2008, the US had increased its installed geothermal capacity to 2.96 GW. California accounted for the lion’s share at 2.55 GW. They were followed by Nevada (at .32 GW) and much smaller facilities in Utah, Hawaii, Idaho, Alaska, and New Mexico.

Geothermal Virtual Plant Tour Link: http://www.calenergy.com/html/aboutus4.asp