Iceland is situated directly astride the Mid-Atlantic Ridge, where the North American and Eurasian tectonic plates slowly separate. This geological boundary creates intense volcanic activity and a shallow heat source. This subsurface heat warms vast underground reservoirs of water, establishing the natural conditions that allow Iceland to be a world leader in sustainable energy use. The country harnesses this natural heat, providing a robust, domestically sourced energy supply.
Harnessing the Geothermal Resource
Accessing this subterranean heat involves a distinction between high-temperature and low-temperature geothermal fields. High-temperature fields, where temperatures can exceed 200°C, are found within the active volcanic zones and are primarily used for generating electricity. Low-temperature fields, generally below 150°C, are typically located in older rock formations flanking the active zone and are mostly utilized for direct heating applications.
The engineering process begins with drilling wells deep into the earth to tap into these superheated reservoirs. In high-temperature areas, the extracted fluid is a mixture of superheated water and steam, which is then piped to power plants. Low-temperature resources are typically hot water, which is pumped directly to end-users via an extensive network.
In many systems, heat exchangers are employed to separate the corrosive geothermal fluid (the primary loop) from clean water (the secondary loop) used for distribution. This isolation prevents the mineral-rich geothermal water from damaging the distribution infrastructure and home heating systems.
Generating Electricity for the Grid
The conversion of high-temperature geothermal resources into electrical power takes place at geothermal power plants. These facilities utilize the heat and pressure of the subterranean fluid to drive turbines connected to generators. The main technologies employed are flash steam and binary cycle systems.
Flash steam plants, the most common type, use hot water from the reservoir, typically over 180°C, which flashes into steam as the pressure drops when it rises to the surface. This high-pressure steam is then directed to spin the turbine blades, generating electricity. Binary cycle plants, in contrast, use a secondary working fluid with a low boiling point, which is vaporized by the geothermal water’s heat to drive a turbine.
Geothermal energy contributes significantly to Iceland’s national grid, accounting for approximately 25% to 29% of the country’s total electricity production. This consistent, baseload power is particularly valuable for energy-intensive industries like aluminum smelting. The spent geothermal water from these power plants is often subsequently repurposed for direct heating applications.
Heating Homes Through District Systems
Iceland operates a geothermal district heating (DH) system, which provides heat and hot water to nearly 90% of the country’s buildings. This system functions by distributing naturally hot water, typically around 80°C, from geothermal reservoirs to residential and commercial properties through a vast network of insulated pipelines. The DH system in Reykjavík is the largest municipal geothermal heating service globally.
Hot water is pumped from the source and delivered directly to consumers for both space heating and domestic hot water use. This centralized approach eliminates the need for individual homes to rely on fossil fuel boilers or electric heating elements. The consistent supply and stable pricing associated with the geothermal source result in substantially lower heating costs for residents compared to conventional fossil fuel systems.
The widespread use of this clean, domestic energy source has resulted in tangible environmental benefits, notably reducing air pollution in urban areas like the capital. By replacing coal and oil for heating, the DH system has dramatically improved the air quality in Reykjavík. The hot water is carefully managed, with the return temperature lowered to around 35°C before being discharged or cascaded for other uses.
Diverse Applications in Industry and Leisure
Beyond large-scale power generation and residential heating, geothermal energy is applied to a wide variety of secondary uses across Iceland. In the agricultural sector, the heat is channeled to maintain greenhouses, enabling the year-round cultivation of produce like tomatoes and cucumbers, despite the subarctic climate. The fishing industry also utilizes geothermal heat for industrial processes, such as drying fish products.
In urban environments, the spent hot water from district heating systems is repurposed to melt snow and ice. This is accomplished by piping the residual heat beneath city sidewalks, parking lots, and roads. This practical application significantly enhances public safety during winter months.
Geothermal heat also fuels the country’s leisure and tourism sectors. The majority of Iceland’s public swimming pools are heated using geothermal water, making swimming a popular pastime even in cold weather. Furthermore, famous geothermal spas, such as the Blue Lagoon, are established by using the discharge water from nearby power plants, creating a unique recreational and wellness experience.