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Volcano range and a geothermal field. Shield volcano mountain range (highest peak 806 m) formed of volcainc ash.
The plateau to the south of the range, Hellisheiði is covered by layers of old and new lava form Hengill’s post-glacial eruptions. The latest eruption occurred in 1000 when Iceland was in the process of Christianization which gave it the name Kristnitökuhraun.
Some folk tales and sagas are connected to the region. For example the one about the troll woman Jóra: She is said to have been lying in wait for innocent wanderers or horsemen on the trail over the Dyrafjöll. In the end, a young farmer shall have put her to death while she slept.
At the foot of the Hengill volcano used be the farm Nesjavellir from 1820 but now it´s the home of Iceland´s largest geothermal power plant, providing Reykjavik with most of it´s hot water and producing electricity.
Extensive geothermal steam field whose energy potential is estimated at 180x1018 Joule second largest after Torfajokull field. Part of this energy resource is being tapped by the Nesjavellir plant.
Because of the special geological situation in Iceland with the high concentration of volcanoes, geothermal energy is very often used for heating and production of electricity. The energy comes rather cheap. So in the wintertime, some sidewalks in Reykjavík and Akureyri are heated and on the road between Reykjavík and the International Airport at Keflavík (40 km long), the lights on the lamp posts are on the whole night.
The Nesjavellir Power Plant supplies 840 l/sec of 83°C water (181,4 F). The water travels through 27 km long pipeline (16,78 miles) to the city with a heat loss of only 2°C on the way. The water corresponds to the heating demands for about 40,000 inhabitants, roughly ¼ of the need in Reykjavik and closest towns. The plant is the most powerful geothermal well in the world.
First holes for the plant were drilled in 1965. Before some greenhouses had utilized the wartmth in the area. The deepest hole was 836 m (0,5 miles). Since then the Heating service has drilled 18 holes and are 13 of them utilized today. The deepest one today is 2265 m (1,4 miles). Each hole provides 20-50 kg of water and steam pr second, steam is normally half or more.
One of the hottest holes had water up to 400°C (XF) at depth of 2 km (1,243 miles). That was to much for the plant to handle so it was filled up with gravel and is now 1580 m (0,932 miles) but still one of the most powerful holes.
Each hole provides 50 MW of usable warmth. Only the warmth is used to heat cold water which is then piped towards Reykjavik.
Nesjavellir stands on the northeast side of the volcano mountain range Hengill.
In Iceland, there are three major geothermal power plants which produce about 17% (2004) of the country's electricity. In addition, geothermal heating meets the heating and hot water requirements for around 87% of the nations' housing.
The first two of the following produce both electricity and hot-water for heating purposes, whereas the third only produces electricity.
1) The Svartsengi Power-Plant, situated in the south-west of the country, near the International Airport at Keflavík on the Reykjanes peninsula. It currently produces 39 MWe of electricity, and about 315 litres/second of almost boiling water (90 °C). The water is also used to heat up the lake of the nearby Bláa Lónið (Blue Lagoon).
2) The Nesjavellir Power-Plant,
3) The Krafla Power-Plant, situated in the north-east corner of Iceland near lake Mývatn and the volcano Krafla - hence the name. It produces 60 MWe of electricity, with an expansion to 90 MWe on the drawing boards. |
