Enormous potential: Deep groundwater could heat half of Denmark
A sea of untapped potential lies deep beneath Denmark. Hot groundwater can be used to cover up to half of Denmark's heating needs according to a comprehensive mapping conducted by, among others, researchers at the University of Copenhagen.
One to three kilometres beneath the earth's surface lies a treasure trove of hot groundwater, which according to the Geological Survey of Denmark and Greenland (GEUS), can be used to sustainably heat up to half of all Danish homes.
A comprehensive mapping demonstrates the potential to harness heat from the earth's interior. The mapping was carried out by researchers from the Department of Geosciences and Natural Resource Management at the University of Copenhagen in collaboration with GEUS and the Department of Geoscience at Aarhus University.
"The brilliant thing about geothermal energy is that it is infinite – it never stops – and it is sustainable because almost no CO2 is emitted," explains Lars Ole Boldreel, an associate professor at the Department of Geosciences and Natural Resource Management at the University of Copenhagen, and one of the main figures behind the study.
Drilling and acoustic wave measurements conducted over past decades demonstrate that large areas deep below Denmark can be used to extract geothermal heat. This is a result of an abundance of areas where porous layers of subsoil sandstone hold vast amounts of hot water – ready to be pumped up and used as a heating source. Large parts of Jutland, Zealand, Lolland, Falster, Møn, parts of Bornholm and elsewhere have favorable subsoil compositions.
Uncertainty about finding the right soil layers
A modest 0.1 percent of Denmark’s current renewable energy is geothermal. There are three geothermal plants in Denmark: one in Amager, Copenhagen; one in Thisted, Northern Jutland; and one in Sønderborg, Southern Jutland.
One of the reasons for our extremely limited use of the tremendous geothermal potential is because there is a bit of uncertainty involved in locating the optimal deep sandstone layers.
"When drilling deep underground, there is a risk that you will overshoot the optimal parts of those sandstone layers with the largest reservoirs of hot water. Our comprehensive mapping allows us to identify the most promising areas for finding hot water and significantly reduces the risk that a well will not reach an optimal layer of sandstone," explains Lars Ole Boldreel.
Some parts of Denmark are not so suitable for extracting groundwater hot enough for district heating. These include parts of the island Funen, and Skagen, in the far north of Jutland. This is partly due to the presence of areas of high bedrock that make it impossible to locate the layers of sandstone at the right depths with enough hot water.
Can help us achieve climate goals
Lars Ole Boldreel admits that while extracting underground energy is no piece of cake, there is significantly less uncertainty in finding hot water than there is in striking oil.
Another advantage of tapping heat from the earth's interior is that doing so has less of an impact upon the environment than exploiting coal and oil.
Average CO2 emissions from geothermal heating plants are just five percent of the emissions from traditional coal-fired power plants. Furthermore, geothermal energy sources are infinite, stable and not dependent upon weather conditions, as is the case with wind and solar energy.
"Therefore, several Danish municipalities are exploring the possibilities for more geothermal plants — to reduce coil and oil consumption and to contribute towards achieving UN climate goals," says Lars Ole Boldreel.
How geothermal energy works
- Geothermal energy refers to the use of heat from the earth's interior, as opposed to ground source heating, where drilling extends a few hundred metres into the ground to supply individual households. Geothermally-heated water between 35 and 90 degrees Celsius is found after drilling wells that are between 1-3 km deep. This extremely hot water can be used to heat entire cities.
- Earth's 5,000-degree Celsius interior constantly pushes heat towards the planet’s surface. This constant heat warms water in porous sandstone layers that can be pumped directly up to the earth’s surface. This heat can then be transferred and used, via district heating networks, to heat radiators in Danish homes. Once the heat has been transferred from the hot groundwater, the cooled groundwater can be injected back down into the sandstone layers where it will be reheated over time.
Source: Geological Survey of Denmark and Greenland (GEUS) and the Danish Energy Agency
Overview of geothermal plants in Denmark
- Thisted, Northern Jutland: Built in 1984 as the first geothermal plant in Denmark. The plant supplies roughly 2,000 households with heat annually.
- Margretheholm, Amager: Built in 2005, intended to supply approximately 4,600 households with heat annually.
- Sønderborg, South Jutland: Built in 2013, intended to supply approximately 2,400 households with heat annually.