This is the first of a two-part aticle describing the acquisition of energy by means of geothermal power. Part I focuses on the Krafla Power Station in Iceland, and how volcanic steam produces electricity. 

There is a land far, far away where upwelling molten magma surges from the ocean floor, birthing new earth.  It is a land where the North American and the Eurasian tectonic plates pull apart like magnetic forces and define what is called the Mid Ocean Ridge.  Coincidently, a large plume of magma connected to the Earth’s core like an umbilical cord is also located on this plate boundary. The excess of billowing hot magma created the youngest country on the planet………Iceland.  The landscape is a vast expanse of fissures, lava-flow deserts, boiling mud-pits, seething hot springs, and volcanic craters of all shapes and sizes.  There are fissures nearly 100 km long where the land on either side is constantly spreading apart at an average of 2 cm a year.

At a depth of 2,500 miles, the earth’s temperature is 3,982 Celsius.   Even a few miles down, the temperature can be over 250 degrees Celsius. As rain and glacial water trickles through the cracks of lithified magma, it collects mineral deposits on its journey to an underground reservoir. The hot water in these geothermal reservoirs can be as much as 370 degrees Celsius. The groundwater is boiled just meters below the volcanic surface only to erupt as sulfuric steam (mwuahahaha).

Geothermal energy is the heat contained within the earth’s core due to the extremely high pressure of the weight of the overlying crust (or lithosphere). Because Iceland is the most volcanically active areas on Earth, it is the best place for development of sustainable energy production. The Krafla volcano is located in northern Iceland where the Krafla Power Station converts the extreme pressures of volcanic steam to electricity.  It all began with trial boreholes in 1974 when seismic activity from the drilling caused corrosive magma vapors to enter the geothermal system and destroy the borehole linings. The first turbine was placed in 1977 but electricity production did not begin until 1978. Energy production haulted when nine volcanic eruptions occurred near the station from 1975-1984, but since then volcanic activity has diminished. 

The Krafla Power Station harnesses thermal energy by using the volcanic steam to drive a turbine wheel.  Steam is piped to the turbine through the boreholes at different pressures where low-pressure steam drives the smaller wheels and higher-pressure steam drives the larger wheels.  As the steam condenses to liquid the pressure drops because liquid molecules are slower than gas molecules.  The change in pressure creates suction which draws the remaining steam down from above, increasing the rotary force of the wheel.  The turbine wheel drives a magnetized rotor inside the generator, inducing an electrical current through a copper coil that surrounds the rotor. The electrical current is then carried along transmission lines to the electricity system and distributed to industries and households. At full capacity the station utilizes 110 kg/sec of 7.7 barr saturated high- pressure steam and 36 kg/sec of 2.2 barr saturated low-pressure steam. The deepest borehole measures 2,222 meters and energy production is 480 Gwh a year. All power stations in Iceland produce 1500 Gwh a year which powers most of the European Union alongside Italy.

Overall, the geothermal process is sustainable because the hot water used can be re-injected into the ground for more steam.  Geothermal energy is also economically stable by reducing reliance on fossil fuels and their capricious prices.  Although the geothermal power plants emit low levels of carbon dioxide, nitric oxide and sulfur, the emissions total about 5% of the levels emitted by fossil fuel plants. There are also emissions-controlling systems that can re-inject the gases back into the ground thereby reducing the total emissions to 0.1% of fossil fuel power plants. No western country can boast as low a level of greenhouse gas emission as Iceland.  Over 26% of Iceland’s electrical energy is of geothermal origin, where 95% of homes are heated using geothermal energy. The country plans to be 100% free of fossil fuels in the near future.

Is this system actually renewable? Although emissions can be recycled, heat and water sources can diminish over time.  It is important to build an appropriate sized plant for certain areas of geothermal activity. Some sites may cool down after decades of use since only so much energy can be stored and replenished in a given volume of the earth.  Luckily some sites can recover after some time depending on the geologic character of the surrounding area. Regions that are more volcanically active have longer-lived energy productions because they have larger reservoirs of heat. A report from the Massachusetts Institute of Technology (MIT) estimated that there is enough energy in the hard rocks only 10 km below the United States to supply the entire world’s energy needs for 30,000 years. Now that’s something to consider!

(1) http://www.lv.is/EN/ April 2008
(2) http://en.wikipedia.org/wiki/Geothermal_power April 2008
(3) Harris, Richard. “Business see green in Iceland’s volcanic power.” Morning Edition,  December 3, 2007 http://www.npr.org/templates/story/story.php?storyId=16780339
(4) http://www.alternate-energy-sources.com April 2008
 

Last update: May 03, 2008
12:51 pm

Published in : Research, Eco Culture

Keywords : green energy geothermal power electricity molten rock seismic magma alternative renewable Iceland

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