Geothermal Energy

Basic facts about geothermal and renewable energy in Iceland

The Earth’s surface consists of large plates known as tectonic plates, which are constantly moving in relation to one another. The plates’ boundaries can be pulling apart (divergent boundaries), colliding (convergent boundaries) or moving sideways (transform boundaries). Iceland is situated on divergent boundaries, between the American and European tectonic plates, which move away from one another at the average rate of 2 cm (nearly an inch) per year. As the plates diverge, volcanoes erupt and fluid molten rock (magma) flows up to fill the void between the plates. Geothermal water originates from cold rainwater that has seeped through Earth’s surface, been heated by magma intrusions and as a result has risen, either to the Earth’s crust or all the way to the surface, creating hot springs/fumaroles.

200°C

The Mid-Atlantic ridge is the division between the American and European tectonic plates. The ridge runs across Iceland and forms an active volcanic belt, stretching from the south-west to the north-east corner. Within the active volcanic belt a number of high-temperature geothermal fields are found. These are areas with water temperature over 200°C at 1000 meters depth. About 32 high temperature fields have been identified in Iceland. Outside the active volcanic belt, 250 of 'low temperature fields' are found. These are defined as areas with temperatures less than 150°C at 1000 meters depth. The closer the low temperature fields are to the active volcanic belt, the higher the temperature.

Hengill Area

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High-Temperature Areas

High-temperature areas are only found on active volcanic belts or along their periphery. There are approximately 20-30 of these areas in Iceland. The volcanic belts lie in a broad area, stretching from the Southwest corner of Iceland diagonally to the Northeast. Water temperature in high-temp areas is 200°C or more at a depth of 1000 meters. The surface activity is much more diverse than in low-temperature areas. Fumaroles are found along hot springs, mud pots and geysers. Generally, soil is very acidic, making it inhospitable to vegetation.

The main high-temperature areas areas in Iceland are on the Reykjanes Peninsula, Krísuvík, Hengill (all in SW-Iceland), Torfajökull and Grímsvötn (S-Iceland), Námaskarð and Krafla (N-Iceland).

Geothermal energy and its origins

High-Steam Pressure

Water in high-temperature areas heats up when it comes into contact with hot bedrock, which is heated by its proximity to magma. Because of the high-temperature, more minerals and gases are dissolved in the water in high-temperature areas. Hence, the water is not utilised directly for heating. However, high steam pressure and thermal power are well suited for heating up fresh water as a hot water supply and for generating electricity, which is precisely what occurs at the Nesjavellir power plant.

Low-Temperature Areas

Low-temperature areas in Iceland, which total approx. 250, can be found all over the country apart from the East and South-east. The largest low-temperature areas lie in southern and western Iceland. The general definition of a low-temperature area is that its temperature is less than 150°C at a depth of 1000 meters.

The temperature is highest in low-temperature areas lying closest to the volcanic belt (mid-Atlantic ridge), but decreases going away from it. Because of the low concentration of minerals in the water in low-temperature areas, the water can be use directly for hot water supply, and is generally deemed safe to drink. When the water heats up it dissolves various substances from bedrock, for example silica and hydrogen sulphide that gives the water its peculiar smell. Reykjavík is a low-temperature area.

Primary energy use in Iceland 1940-2014

Geothermal is Iceland´s single largest source of energy today.