Geothermal electricity is generated from the earth’s geothermal energy. Technologies in use include dry steam power plants, flash steam power plants and binary cycle power plants. The graphic below represents installed geothermal capacity by technology type.
Geothermal electricity generation is currently used in 24 countries, while geothermal heating is in use in 70 countries. Geothermal energy is considered a renewable source of energy. The graphic below indiactes that geothermal energy takes care of 0.12 % of total global energy consumption.
The Current worldwide installed capacity is 10,715 MW, with the largest capacity in the USA of about 3,000 MW. In El Salvador, Kenya,The Philippines, Iceland and Costa Rice more than 15% of the electricity originates from geothermal sources.
Geothermal power is considered to be sustainable (renewable) because the heat extraction is small compared with the Earth’s heat content.The CO2 emission from existing geothermal electric plants is only 10-12% of a conventional coal-fired plant.
Geothermal electric plants have until recently been built exclusively where high temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology may enable enhanced geothermal systems over a much greater geographical range. Several demonstration projects are operational in Germany and France. However an earlier effort in Basel, Switzerland was shut down after it triggered earthquakes.
The thermal efficiency of geothermal electric plants is low, around 7-10%, because geothermal fluids are at a low temperature compared with steam from boilers. Because geothermal power does not rely on variable sources of energy, unlike, for example, wind or solar, its capacity factor can be quite high (up to 96%). However the global average capacity factor was 74.5% in 2008, according to the IPCC.
Geothermal power requires no fuel, it is therefore immune to fuel cost fluctuations. However capital cost tend to be high. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. Enhanced geothermal systems tend to be on the high side of these ranges, with capital costs above $4 million per MW installed capacity. The cost of producing electricity from geothermal sources is estimated to be 5-6 cents/KWhr.
3. Advantages and Disadvantages
Fluids drawn from the deep earth carry a mixture of gases such as CO2, hydrogen sulfide, methane and ammonia. These pollutants contribute to global warming, acid rains and noxious smells if released. Plants that experience high levels of acids and volatile chemicals are usually equipped with emission-control systems to reduce the exhaust.
In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxic chemicals, such as mercury, arsenic and antimony. These chemicals come out of solution as the water cools, and can cause environmental damage if released.
Plant construction can adversely affect land stability. Subsidence has occurred in New Zealand. Enhanced geothermal systems can trigger earthquakes as a result of hydraulic fracturing.
The project in basel Switzerland was suspended because more than 10,000 seismic events measuring up to 3.4 on the Richter scale occurred over the first 6 days of water injection.
The risks associated with exploiting geothermal power at large scale resembles the risks associated with large scale fracking. Drilling in the Earth to great depth and thereby destroying the earth’s geo-structures has proven to involve increased geo-risks, creating local earthquakes.
A similar situation has arisen in the Netherlands over the last five years, where the earthquake intensity and frequency has greatly increased as a result of the greatly increased rate of gas exploration. These earthquakes between 3 and 3.8 on the Richter scale have led to substantial infrastructure damage and substantial local social unrest.
4. Summary and conclusion
Some sources suggest that geothermal energy has great promise for the future. It is estimated that as much as 2000 GW could be produced from geothermal sources in the future. However the capital costs are relatively high and the geo-risks of earthquakes are high.
Geothermal energy also produces green house gases, although much less compared with will fossil fuel based energy generation facilities.
Recent experiences with gas exploration, natural-gas fracking and geothermal exploration have shown that the risks of earthquakes are high and social protests are rising in many regions in the world.
Any energy generation technology that involves geo-risks, nuclear fall-out risk or global warming should be gradually phased out in the future.
New energy generation technologies are now emerging. These energy technologies are clean, can be apllied at small scale, involve no risk, create no damage to the earth’s geo-structures, cause no air pollution, no radio active waste and are much cheaper then any energy technology sofar.