by Einar Tjorvi Eliasson and Svavar Jonatansson, Virkir-Orkint Consulting Group Ltd, Reykjavik

In this article we will endeavour to describe the utilisation of geothermal energy in Iceland and its diversified role in our economy. It was made possible by the willing advice and assistance of a number of geothermal experts employed by Orkustofnun (the National Energy Authority of Iceland), who supplied all the data and most of the illustrative material.

Iceland is a volcanic island about 800 to 900 km north-west of Scotland and inhabited by about 265 thousand people. Iceland is about 75% of the size of Scotland or some 104,000 km2 in area, only one eighth of which constitutes arable land. Like the islands of Scotland it has very few trees, though it was largely wooded at the time of settlement. Iceland was occupied in the ninth century chiefly by Norse Vikings, many of whom stopped in Ireland and Scotland en route making off with young men, women and miscellaneous material goods. Celtic influence is therefore manifest in the Icelandic national character, and an important part of the nation’s heritage. The national language is Icelandic, the old Norse language little changed through centuries of isolation and farsighted efforts at keeping it unadulterated.

Well into the nineteenth century the nation eked a living mainly from sheep farming and fishing. The two world wars brought about great changes, particularly the second one. Iceland received its independence from Denmark in two stages, home rule in 1918 and full independence in 1944. This latter feat marked the turning point in the nation’s fortunes both as regards its economic growth and its social achievements. In the last sixty years the Icelandic nation has changed from a rural into a modern high technology urban society. This was largely made possible by the development of two abundant indigenous energy resources available in Iceland, namely geothermal energy and hydro-power.

The country straddles the tectonic plate boundary known as the Mid-Atlantic Ridge. It has been the location of periodic volcanic eruptions from Miocene time to the present.

Like other constructive plate margins, the Mid-Atlantic Ridge is characterised by a very high heat flow. The regional temperature gradient, as measured in numerous drill holes in low-permeability rocks away from the geothermal fields, varies from about 50 to 1500C/km. This is two to five times higher than the average thermal gradient of the world. Iceland is enfolded in the warm Gulf Stream and precipitation is high. The country is thus very rich in both hydro-power and geothermal resources.

It has become customary to divide the geothermal activity in Iceland into two categories on basis of the maximum temperature in the uppermost 1 km of the formations. In low-temperature areas this temperature is lower than 1500C, but higher than 2000C in the high temperature areas.

To date about 250 separate low-temperature areas with over 600 hot springs (temperature over 200C) have been located. There exist moreover 26 high-temperature areas with steam fields. The high-temperature areas are directly linked to the active volcanic systems. The low-temperature systems form under conditions where rain water descends deep into the bedrock, draws heat from it as it ascends along fractures and dykes driven by the hydrostatic gradient and convection caused by the lighter density of hot water relative to that of cold water.

Iceland has the world’s third highest per capita consumption of energy, or about 103,000 kWh (372 GJ) per year per head of population.

Geothermal energy provides 44% of the primary energy consumption in Iceland, hydro-power 16%, imported oil 38% and imported coal 2%. Thus 60% of the total primary energy is supplied from indigenous sources. Fossil fuel is used almost exclusively for motive power in the transportation sector and the large fishing fleet.

The economically exploitable part of the geothermal energy resource is difficult to estimate accurately, but it is clear that only a small part of the geothermal energy resource has been tapped so far.

Geothermal energy has a multitude of useful applications in Iceland, the most important of which are:

  1. Space heating (73.8%).
  2. Electricity production (4.3%).
  3. Industrial use (9.1%).
  4. Horticulture (3.8%).
  5. Pisciculture (2.8%).
  6. Health uses (4.5%).
  7. Snow melting (1.7%).

It can be seen that space heating is by far the greatest use of geothermal in Iceland, about 85% of all working and living space being heated that way. Geothermal hot water and steam are moreover used in many novel ways in industry, typically on a small scale. The financial benefits of geothermal space heating alone as regards the import of fossil fuel comprises an annual saving of some 100 million US dollars. Environmental benefits are enormous. Currently there are some 30 municipal district heating systems, or “hitaveitas”, operating in Iceland serving about 218 thousand people. The world’s largest “hitaveita” is the Reykjavík District Heating Service, serving some 145 thousand people or more than half the population. In addition to the municipal ones, there are over 200 geothermal heating systems serving individual farms, groups of farms and/or clusters of summer cabins found throughout the country. They serve in total some 4 thousand people.

In the following each type of utilisation will be described in outline and an endeavour made to detail the more salient points.

  1. Space heating

    The total installed geothermal capacity for direct use in Iceland is about 1,443 MWt, and the energy use about 4,500 GWh/year (16,300 TJ/year). The cold climate requires heating most of the year resulting in ideal economic conditions for direct use of geothermal energy for space heating. Archaeological evidence suggests that the great saga writer Snorri Sturluson (early thirteenth century) may have been amongst the earliest users of geothermal hot water for heating in Iceland. Snorri also used it for bathing in the famous Snorralaug. Systematic use of geothermal space heating started when hot water was piped to the first houses in Reykjavik in 1930, from hot springs and shallow wells on the then outskirts of the city. The district heating systems are largely owned by the local communities. Iceland has for a long time been the world leader in geothermal district heating. Even before the first oil crisis in 1973 about 50% of the population heated their houses thus. After the oil crisis a concentrated effort was made, which resulted in 85% of the heating market being supplied by geothermal energy by about 1985. The geothermal water used for space heating in Iceland comes mostly from reservoirs with aquifer temperatures of 60-1300C, and commonly has total dissolved solids of 200-400 ppm. This water can, in most cases, be used directly from the wells (i.e. without the use of heat exchangers or chemical treatment). The water is typically pumped to the surface by the use of lineshaft driven pumps placed at 100-250 m depth to insulated storage tanks. The tanks serve to balance short time variations in the demand, particularly in the large heating systems. The Reykjavík District Heating Service hit on a novel idea to make a large storage tank cluster that is located on top of a hill centrally within the city visually more attractive. The company built a rotating restaurant cum conference centre, called The Pearl (Perlan) around a cluster of six large storage tanks. The Pearl has now become one of the attractions in Reykjavík for foreign and native tourists alike. In a few cases, oil-fired peak load stations are used to meet the demand during the coldest days of the year. On average it takes about 1.6 m3 of 800C water to heat each m3 of living space annually (80 kWh/m3). The spent water from the house systems is disposed of, typically at about 350C, to the sewage system. It is becoming more and more common to use this return water for the de-icing of pavements before final disposal. Four district heating systems have, in part, a two pipe system, the return water being used to adjust the supply temperature to households to 800C, and in the town of Akureyri a heat pump has been installed to make better use of the thermal energy. Four municipal district heating systems harness high-temperature steam fields, with reservoir temperatures of 180-3500C. In such cases, the high enthalpy fluid (steam and water) is used to heat fresh groundwater in heat exchangers and the heated water is subsequently transported by insulated pipes to the communities, often over large distances (27 km in the case of the Nesjavellir Plant). The most notable examples of such a development are the Svartsengi field for the communities on the Reykjanes peninsula and the Nesjavellir field for the capital city of Reykjavik. Both fields are designed for the cogeneration of hot water for space heating and electricity to increase the thermal yield from the fields. The brine from the Svartsengi steam separator plant is discharged at the surface into a large lagoon, called The Blue Lagoon. The lagoon is much used for bathing by the local populace and foreign tourists, because of its rustic situation and the health benefits to be derived from bathing in the brine. Research has shown that bathing in the brine is beneficial to those who suffer from psoriasis and rheumatic afflictions.

  2. Electricity production

    Geothermal power is produced for the national grid in three high-temperature areas: Krafla, Bjarnarflag, and Svartsengi. The Krafla plant was originally constructed in the 1970’s to house two 30 MWe dual pressure turbines. The installation of one was delayed because of inadequate steam supply, which was due to volcanic activity in the area and impulses of magmatic gases into the reservoir. Volcanic activity only about 2 km from the plant location started in 1975 and continued intermittently until 1984 (in all 9 episodes). The associated magmatic effects on the geothermal reservoir ranged from causing rapid clogging up of the wells to acidifying the geothermal water making it temporarily unsuitable for use. The Bjarnarflag field has been exploited to provide steam for a mineral processing plant, Kísilidjan, since 1967. It also supplies steam to Iceland’s first commercial geothermal electric plant (3 MWe), built in 1969. The Bjarnarflag field is located some 11 km south-west from Krafla. The unique Svartsengi Geothermal Plant is a cogeneration plant producing simultaneously both hot water for heating and electricity for the national power grid. The plant design emphasises extracting as much thermal energy as practicable from each tonne of geothermal fluid withdrawn from the reservoir. This has been attained combining hot water and electricity production plus using the effluent for bathing purposes.

  3. Industrial use

    The Kísilidjan Diatomite Plant started operation in 1967. It produces diatomaceous earth filter-aids (24,000 tonnes yearly) used for the filtering of industrial organic liquids, such as dry cleaning fluids; beverages like wine and beer and various pharmaceuticals. The raw material comprises siliceous shells of diatomaceous algae from lake Mývatn that thrive there because of the silica rich geothermal inflow to the lake. Deposits of this valuable material are found in other parts of the world, for instance on the Isle of Skye. Iceland is the only country, which uses wet deposits of diatomite for this production. The reason is the availability of geothermal steam for drying of the raw material prior to processing. Geothermal heat is also used for de-icing purposes to make possible an all year round operation of the plant. Geothermal energy is used in miscellaneous other industrial type applications such as for instance in fish drying, in the drying of seaweed, in wool washing, in carbon dioxide gas production and hay drying on farms. In addition to these industrial processes, geothermal energy is used for such varied purposes as lumber drying, food processing, steam baking of bread and curing of cement blocks. A sea chemicals plant was operated at Reykjanes for over twenty years producing yearly about 10,000 tonnes of common salt. The plant received both its raw material and power from a single geothermal well (2950C). The salt was produced from the geothermal brine, after silica removal, it is very low in sodium and has been found highly beneficial for those plagued by hypertension.

  4. Horticulture

    Geothermal heating of greenhouses started in Iceland in 1920. Low-temperature water is used in many localities for greenhouses producing vegetables (mushrooms, tomatoes, cucumbers, peppers, lettuce, eggplants, etc.) and flowers for the domestic market. Some 18 hectares are under glass at present and there are 10 hectares of soil-heated nurseries. The use of artificial lighting has achieved lengthening of the growing season from six to nine months. The output of these greenhouses is sufficient to satisfy the national market demand for at least six months of the year. Hot water is also used in the growing of tree seedlings for the new efforts in reforestation of the country, large regions of which are barren.

  5. Pisciculture

    Pisciculture based upon low temperature geothermal water is quite common in Iceland. Currently there are 75 registered fish farms in the country and seven research stations. The types of fish most commonly reared are salmon, arctic char, rainbow trout and brown trout. Trial farming of red abalone, cod and halibut has been ongoing for several years. There are three different types of salmon farming scenarios currently in operation in Iceland, namely ocean ranching, shore based fish ponds and floating fish cages. The role of geothermal in pisciculture is to heat the rearing water up to the optimal growth rate temperature of 80C to 140C depending upon the type of fish and the rearing stage. The fresh water temperature in the ground water aquifers of Iceland is about 40C to 60C and the sea water ranges in temperature from 10C to 90C. Large quantities of inexpensive heat must therefore be available and this is supplied by the geothermal water. Only very low temperature geothermal water (200C to about 500C) is used, chiefly because it is suitable for direct use. The temperature of the ocean close to the shores of Iceland typically ranges between 10C in winter to 110C in summer. Farming fish in cages floating along the shore can only be carried out in a few sheltered places and only for a limited period in the year. The fish are therefore reared for a few months in summer in the floating cages and for the rest of the year in land based rearing stations.

  6. Health uses

    Geothermal energy use was from the time of settlement some 1100 years ago until early this century almost entirely limited to bathing, washing of clothing and cooking. This use of geothermal energy is today still significant and the heating of swimming pools the second most important type of use after space heating. This is clearly demonstrated by the fact that the total surface area of the 120 public swimming pools in Iceland is about 23,000m2. Most of the pools are open air pools in constant use throughout the year, something only possible because of the inexpensive geothermal energy. The pools both serve for instruction in swimming, which is compulsory in schools, for keep-fit and recreational purposes. Swimming is very popular in Iceland and in the greater Reykjavík area alone there are ten public outdoor pools and three indoor ones. The largest of these is the Laugardalslaug having a surface area of 2,500m2 and five hot tubs in which the water temperature ranges from 350C to 420C. Other health uses, such as the Blue Lagoon, the Health Facility in Hveragerdi comprising geothermal clay baths and water treatments, are gaining way. Production of geothermal health salts and miscellaneous ointments is also a growing industry. Icelandic private enterprises are also increasingly setting their sights on the health tourist industry.

  7. Snow and ice melting

    The installation of snow-melting systems, based mostly upon the use of spent geothermal water from the house heating systems, is a new and growing geothermal utilisation sector in Iceland. It started about 10 to 15 years ago and finds use in the melting of snow off pavements, car-parks, drive-ways and roads. The total area currently covered by such systems is estimated to be 350,000m2 for the country as a whole, of which 250,000m2 are in the capital. The systems are normally designed for a thermal output of 180 W per m2 and the average annual energy consumption is found to be 250 to 375 kWh per m2, strongly dependent upon the prevailing weather conditions.