Geothermal Energy

"Heat from the earth can be used as an energy source in many ways, from large and complex power stations to small and relatively simple pumping systems. This heat energy, know as geothermal energy, can be found almost anywhere – as far away as remote deep wells in Indonesia and as close as the dirt in our backyards. Tapping geothermal energy is an affordable and sustainable solution to reducing our dependence on fossil fuels, and the global warming and public health risks that result from their use."

"Under the Earth's crust, there is a layer of hot and molten rock called magma. Heat is continually produced there, mostly from the decay of naturally radioactive materials such as uranium and potassium. The amount of heat within 10,000 meters (about 33,000 feet) of the Earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world." "Geothermal energy is contained in underground reservoirs of steam, hot water, and hot dry rocks. As used at electric generating facilities, hot water or steam extracted from geothermal reservoirs in the Earth's crust is supplied to steam turbines at electric utilities that drive generators to produce electricity. Moderate-to-low temperature geothermal resources are used for direct-use applications such as district and space heating. Lower temperature, shallow ground, geothermal resources are used by geothermal heat pumps to heat and cool buildings."

"There are three designs for geothermal power plants, all of which pull hot water and steam from the ground, use it, and then return it as warm water to prolong the life of the heat source.

  • In the simplest design, the steam goes directly through the turbine, then into a condenser where the steam is condensed into water.
  • In a second approach, very hot water is depressurized or 'flashed' into steam which can then be used to drive the turbine.
  • In the third approach, called a binary system, the hot water is passed through a heat exchanger, where it heats a second liquid – such as isobutane – in a closed loop. The isobutane boils at a lower temperature than water, so it is more easily converted into steam to run the turbine.

"The largest geothermal system now in operation is a steam-driven plant in an area called the Geysers, north of San Francisco, California. . . . Today, the Geysers has a capacity of 850 MW, which still meets nearly 70 percent of the average electrical demand for California's North Coast region." "The plants at the Geysers use an evaporative water-cooling process that pulls the steam through the turbine, producing power more efficiently. But this process loses 60 to 80% of the steam to the air, not reinjecting it underground. . . . . Some efforts are underway to remedy the situation, including the Santa Rosa Geysers Recharge Project, which involves injecting treated wastewater from neighboring communities through a 40-mile pipeline. Recharging the existing reservoirs is estimated to increase output by 85 MW, providing enough electricity for approximately 85,000 homes."

"One concern with open systems like the Geysers is that they emit some air pollutants. Hydrogen sulfide – a toxic gas with a highly recognizable 'rotten egg' odor – along with trace amounts of arsenic and minerals, is released in the steam. In addition, at a power plant at the Salton Sea reservoir in Southern California, a significant amount of salt builds up in the pipes and must be removed. . . . With closed-loop systems, such as the binary system, there are no emissions; everything brought to the surface is returned underground."

There are a number of advantages for using geothermal energy to generate electricity:

  • "Clean. Geothermal power plants, like wind and solar power plants, do not have to burn fuels to manufacture steam to turn the turbines. Generating electricity with geothermal energy helps to conserve nonrenewable fossil fuels, and by decreasing the use of these fuels, we reduce emissions that harm our atmosphere.
  • 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.
  • Reliable. Geothermal power plants are designed to run 24 hours a day, all year. A geothermal power plant sits right on top of its fuel source. It is resistant to interruptions of power generation due to weather, natural disasters or political rifts that can interrupt transportation of fuels.
  • Flexible. Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity.
  • Keeps Dollars at Home. Money does not have to be exported to import fuel for geothermal power plants. Geothermal 'fuel' - like the sun and the wind - is always where the power plant is; economic benefits remain in the region and there are no fuel price shocks.
  • 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 by bringing electricity to people far from 'electrified' population centers."

"In 2003, geothermal was the third largest source of renewable energy in the United States." "As the world's largest producer of geothermal energy, the U.S. generates a yearly average of 15 billion kilowatt hours of power, comparable to burning about 25 million barrels of oil or 6 million short tons of coal per year or 150 billion cubic feet of natural gas." "The availability of renewable resources in the U.S. varies significantly by region. In areas where geothermal resources are available, such as California, the percentage of electricity derived from geothermal sources can exceed 7 times the national electricity average. Most geothermal production is concentrated in the western states." "In California, the state with the largest amount of geothermal power on-line, electricity from geothermal resources accounted for 5 percent of the state's electricity generation in 2003 on a per kilowatt hour basis."

"The U.S. Geological Survey estimates the geothermal resource base in the United States to be between 95,000 and 150,000 MW, of which about 22,000 MW have been identified as suitable for electric power generation. Unfortunately, only a fraction of this resource is currently utilized, with an installed capacity of 2,800 MW (worldwide capacity is approximately 8,000 MW)."

Geothermal energy is gaining in popularity for heating and cooling buildings and homes. Geothermal heat pumps, also known as ground-source heat pumps, tap into the constant year-round temperature of 50ºF that is just 5-10 feet underground. "Either air or an antifreeze liquid is pumped through pipes that are buried underground, and recirculated into the building. In the summer, the liquid moves heat from the building into the ground. In the winter, it does the opposite, providing pre-warmed air and water to the heating system of the building." In the simplest use of ground-source heating and cooling, a tube runs from the outside air, under the ground, and into a house's ventilation system. More complicated, but more effective systems use compressors and pumps – as in electric air conditioning systems – to maximize the heat transfer." "In regions with temperature extremes, such as the northern United States in the winter and the southern United States in the summer, ground-source heat pumps are the most energy-efficient and environmentally clean heating and cooling system available." "A study by the U.S. Environmental Protection Agency found that they are as much as 72% more efficient than electric heating and air conditioning systems. The U.S. Department of Energy found that heat pumps can save a typical home hundreds of dollars in energy costs each year, with the system paying for itself in 2 to 10 years."

"By the end of 2005, more than 600,000 ground-source heat pumps were installed in the United States, with new installations occurring at a rate of 50,000 to 60,000 per year. While this is significant, it is still only a small fraction of the U.S. heating and cooling market, and several barriers to greater penetration into the market remain." "For example, despite their long-term savings, geothermal heat pumps have higher up-front costs. In addition, installing them in existing buildings can be difficult, since it involves digging up the yard around a house (provided it has a yard). Finally, many heating and cooling installers are just not familiar with the technology." Nevertheless, ground-source heat pumps are growing in popularity in some areas. "In rural areas without access to natural gas pipelines, homes must use propane or electricity for heating and cooling. Heat pumps are much less expensive to operate, and since buildings are widely spread out, installing underground loops is not an issue."

"Geothermal energy has the potential to play a significant role in moving the United States (and other regions of the world) toward a cleaner, more sustainable energy system." "It is one of the few renewable energy technologies that – like fossil fuels – can supply continuous, base load power." "The costs for electricity from geothermal facilities are also declining. Some geothermal facilities have realized at least 50% reductions in the price of electricity since 1980. New facilities can produce electricity for between 4.5 and 7.3 cents per kilowatt-hour, making it competitive with new conventional fossil fuel-fired power plants." "Over the next decade, new geothermal projects are expected to come online to increase U.S. capacity to between 8,000 and 15,000 MW. . . . In addition to electric power generation, which is focused primarily in the western United States, there is a bright future for the direct use of geothermal resources as a heating source for homes and businesses everywhere."


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