Reykjavik: The ground heats the city

Reykjavik has, for a long time, held the title of the world's largest and most sophisticated geothermal heating user, drawing up hot water from natural springs to heat its buildings as early as 1930. Today, geothermal energy powers the entire city - with an electricity network harnessing 750 MW of thermal power from steam, and a hot water distribution system generating 60 million cubic meters of hot water annually. In 2006, 26.5% of electricity in Iceland was derived from geothermal energy, 73.4% from hydro power, and only 0.1% from other sources. As the figures clearly illustrate, the use of this natural resource has massively reduced Reykjavik's dependence on fossil fuels and made it one of the cleanest cities in the world. The city's use of geothermal energy has prevented as much as 110,000,000 tons of CO² from entering the atmosphere between 1944 to 2006 and presently saves up to 4 million tons from being emitted annually. Geothermal energy has also contributed to Iceland's transformation from a relatively poor country to one that enjoys a very high standard of living. 

The special geological condition of Iceland that allows it to take such a huge advantage of geothermal energy is its location along the Mid Atlantic ridge - a deep sea mountain range with a high concentration of volcanoes. Specifically, Iceland gets most of its heating and electricity from five power/heating plants that are located 30 km east of Reykjavik in a particularly geothermal energy-rich area. Geothermal heat originally comes from the Earth's core, where temperatures may reach 4,000-7,000°C. This heat can come to the surface  in the form of  hot water that seeps through fissures, cracks and permeable rock. A number of countries and continents, including Iceland, sit over terrain with a lot of these fissures and cracks, allowing them to easily take advantage of these naturally occurring heat supplies. Over the years, the United Nations University Geothermal Training Program and Iceland's National Energy authority were established in order to help developing countries meet their potential for geothermal energy use.

Presently, the company Reykjavik Energy serves about 170,000 people, drawing up 63 million cubic meters of hot water for thermal use annually. Space heating accounts for 85% of this water, while bathing and washing account for 15%. The "space heating" category includes the heating of houses, swimming pools, some greenhouses, and (increasingly) roads and sidewalks that accumulate snow.

Typically, Reykjavik Energy draws up water from low temperature fields (with temperatures below 150°C located roughly 1000 m below the surface) as well as high temperature fields (with temperatures above 200°C located far below the 1000 m depth line).  Water from low temperature fields can be used as hot tap water or can directly space heat buildings after it is sent into the city's distribution system consisting of over 1,300 km of piping.  Water from high temperature fields is used for electricity generation and must pass through heat exchangers and treatment facilities before it can enter the city's distribution system. In this system, water that has cooled is either re-circulated and reheated by adding hotter water, or drains directly into the sewer system.