The heat source beneath our feet
Geothermal heating is gaining a foothold, but accounts for only a small share of the renewable heat sources used globally. The benefits are plenty. Long-term, it is cost-effective, stable and clean, but initial costs are high
Geothermal hot springs are right below our feet and offer numerous benefits in a decarbonising world. Used for bathing, heating and cooking for thousands of years, hot springs are also comfortably familiar. Yet, geothermal heating still only accounts for a modest part of the renewable heating sources used around the world.
“Geothermal heating has enormous potential,” says Lars Andersen, managing director at Geoop, a Danish geothermal firm. “Ninety-nine per cent of the Earth’s volume has temperatures above a thousand degrees centigrade. If we were to start from scratch and build a whole new energy system, a lot more would be based on geothermal heat.”
Geothermal heating is extracted from hot water found underground. Temperatures near the crust of the earth are not very high, however. Heat from the earth’s core flows to the crust, cooling by about 25°C for every kilometre nearer the surface. Areas near tectonic plate boundaries and volcanic activity have the highest temperatures.
Ring of fire
“Basically, it is the Ring of Fire, where the continental plates lie, where you see by far the biggest potential,” says Andersen, referring to the horse-shoe shaped area in the Pacific Ocean characterised by earthquakes and volcanic eruptions. Iceland, too, fits the bill with its many volcanoes and hot springs, which can reach 100°C or more. Indeed, geothermal energy meets the heating and hot water requirements of most of the country’s homes.
“But you cannot transfer experiences from one place to another if you don’t have the same underground conditions and temperatures,” says Brian Vad Mathiesen, energy professor at Aalborg University, underlining that geothermal conditions in Iceland are “completely different” than in Denmark.
Geothermal resources are used in more than 80 countries, though primarily for electricity generation, with only a limited number of countries using them for heating. In 2017, geothermal heating produced a modest 14.1 Mtoe, compared to more than 400 Mtoe of heat produced by bioenergy and renewable electricity, says the International Energy Agency (IEA). The share of geothermal heating is forecast to rise to 20 Mtoe in 2023, when bioenergy and renewable electricity will generate 485 Mtoe of heating, the agency says.
China and Turkey accounted for 80% of geothermal heating consumption in 2017. Rapid growth in China accounted largely for nearly a doubling of that consumption globally from 2012 to 2017. Turkey benefits from being located in an active tectonic area. In China, studies have identified more than 3000 hot springs and more than 300 geothermal fields have been investigated and explored, says the World Energy Council.
Globally, most geothermal heat is used for bathing (45%) and space heating (34%). The technology is widely applied in agriculture, primarily to heat greenhouses, in some countries, such as the Netherlands, which is now the fourth-largest user of geothermal heat in the agriculture sector after China, Turkey and Japan, says the IEA.
The municipality of Hedensted in Denmark has constructed a climate road. The 50-metre stretch of highway aims to solve two climate challenges: absorb the increasing amount of extreme rainwater caused by climate change and reduce carbon dioxide emissions.“Water is collected below the road, where geothermal pipes are installed,” explains Merete Valbak, the municipality’s climate coordinator. The pipes extract and condense energy from the rainwater and create heat for use by the nearby nursery. She adds: “Testing is still going on, so we do not have results from a full year yet. But we know the nursery has received heat from the climate road and has been able to switch off its normal heat supply.” The next step will be to test whether the climate road can potentially heat an entire residential area.Permeable asphalt on the climate road allows the rainwater to penetrate and flow into the ground below. This prevents it from running into the sewage system and stops flooding, avoiding dangerous conditions for drivers. Increasing quantities of rainwater are a real problem in many areas. ”Climate roads could be a solution,” says Valbak, leading water below ground to be stored until water levels have reduced and it can be released back into nature.The climate road is part of an EU-supported project, involving municipalities, universities and utility companies, looking at climate adaptation in the Central Denmark region.
Heating Paris
In Europe, new geothermal heat installations are mainly focused on district heating. In the EU, nine plants came into operation in 2017, adding 75 megawatts thermal of new capacity in France, Italy and the Netherlands. “There is real potential for geothermal heating in Europe. I think it may be even bigger than heating from solar energy if we exploit it properly,” says Vad Mathiesen. A realistic guess is that geothermal heating can be the source for 10–15% of district heating, he adds.
Many European countries have excellent geothermal sources, but lack the district heating infrastructure needed for geothermal to be cost-efficient. How big a part geothermal will play in district heating “depends on the sources available and the investments you are willing to make”, says Vad Mathiesen. “It is not a new technology and many places in Europe have really good experiences [of it].”
He cites Paris as a positive example. The French capital has used geothermal heating for 30 years and subsidies were the driver, adds Andersen. The city has 34 geothermal heating plants. Heat is extracted from water between 1500 and 2000 metres below ground at temperatures of 55–85°C, says BRGM, a French geological survey institute.
In some places, where temperatures are too low, heat pumps can help. These are a “game changer”, says Philippe Dumas, secretary general at the European Geothermal Energy Council (EGEC). “With heat pumps we can produce geothermal heat anywhere in Europe.” Only around 1.5 million individual geothermal heat pumps have been installed in Europe to date so “there really is potential”, says Dumas, although he admits there is competition from biomass and gas.
Competition with biomass is a stumbling block in Denmark. “Geothermal has the potential to heat up to 500,000 Danish homes,” says Peter Bjerregaard from E.ON, one of the three companies behind Geoop. “But there are obstacles.” Geoop hosted a meeting with representatives from industry and politics on geothermal heating at the Danish parliament in February 2019.
The main obstacle is the tax exemption on biomass, which fuels around half of district heating in Denmark. Heat pumps, needed to raise the temperature of the water found underground from around 60°C to 80–90°C, are powered by electricity, which carries a tax, explains Bjerregaard. “We see a clear wish from municipalities to use geothermal heating,” he says. But while there is a tax on electricity, it is difficult to make a business case for geothermal.
Costs and subsidies
Geothermal heating is a cost-effective, stable source for heating and, once established, practically carbon dioxide neutral. High up-front investments are, however, needed before it can be widely applied across Europe to fund drilling for suitable wells and the construction of district heating infrastructure, still lacking in many European countries.
“It is cheaper to buy a boiler, fired by gas, oil or even biomass, but afterwards, costs of fuels and biomass are high. The upfront investment for geothermal heat is high, but there are not many costs after,” says Andersen.
Putting a price on carbon could help geothermal heating to become more widespread in Europe, says Dumas. He also suggests allowing EU member states to set up technology specific support to help decarbonise the heating and cooling sector. “This would help increase security for investors and provide financing for new projects,” he says.
Biomass will start to lose its competitive advantage, even if taxes do not change, forecasts Bjerregaard. “Global demand for biomass is expected to rise significantly in the coming decades and sustainability requirements will lead to price increases,” he predicts. “Geothermal heating, on the other hand, can deliver stable heating for hundreds of years, giving it the competitive advantage of supporting the green transition in the long term.”
This article by Karin Jensen is part of a series examining how to decarbonise heating and cooling systems from FORESIGHT Climate & Energy
