© BMWi
What exactly is geothermal energy?
An inexhaustible source of energy
Some 6,350 kilometres beneath our feet, liquid iron seethes at temperatures of up to 7,000 degrees Celsius. The idea of using this energy would have certainly warmed the cockles of Jules Vernes’ heart. The temperature decreases the closer you move towards the surface. In the top 10 kilometres of the earth’s crust, the temperature is an average of just 15 degrees Celsius. However, it has been calculated that the heat contained within the earth’s outermost layer is sufficient enough to cover the current energy needs of all the entire global population. It could do this more than 100,000 times over, electricity generation included.
Beneath the surface of the Federal Republic of Germany alone, there is enough heat at 3 to 7-kilometre depth to supply Germany with the energy it needs for 10,000 years – right around the clock, irrespective of the weather, and without harming the climate. The specialist term to describe this source is ‘geothermal’ heat. This is the heat energy that is stored underneath the surface of the earth.
Drawing heat energy up to the surface
Geothermal energy is already being used from below the earth’s surface to the heat houses and cities that lie above. The extensive technical processes used are split up into the categories ‘near-surface’ and ‘deep’ geothermal energy, depending on the depth of the borehole.
Near-surface geothermal heat goes down up to 400 metres in depth. To harness it, pipes carrying a special transport fluid – often water mixed with anti-freeze – are inserted into the ground. Put simply, these pipes fetch the heat underneath the ground and transport it to so-called heat pumps, such as the ones found in the home. These extract the heat from the transport medium. This heat is then distributed to be used for heating, to make the living room nice and cosy, or to heat the water, in order to provide hot showers.
Deep geothermal systems go down much further. They might use warm groundwater located approximately 4,500 metres underground or go down into hot rock found up to 5,000 metres below the surface. The technical preparations that have to be undertaken in order to set up and use this kind of geothermal energy are very extensive. The benefits, however, can be enormous. Deep geothermal energy can be used to supply entire localities or districts with heat and electricity.
A 7.4 per cent share in Germany’s renewables-based heat generation
One city that has recognised the potential held by geothermal energy is Munich. By 2040, the city hopes to become the first in Germany to derive all of district heating from renewables. In order to make this happen, its public utilities are focusing on the use of geothermal energy.
In 2015, geothermal energy combined with heat from the outside air and from groundwater delivered 11.4 billion kilowatt hours of heating in Germany. That is equivalent to a pretty respectable 7.4 per cent of all green heat that was generated in Germany in 2015. However, the lion’s share of renewables-based heat is produced from solar energy or biomass. This involves the use of solar thermal installations and pellet heating.
Renewables-based heating becoming more important – and more attractive
Geothermal energy is only one source of renewable energy used to produce heat. But the need to generate heat from renewables is most definitely there and is continuing to rise. By 2050, the German government wants to have brought down primary energy demand for buildings, i.e. demand for fossil fuels such as oil and gas, by around 80 per cent.
The first fruits of this are now being seen. In 2015, the share of renewables used in heat generation in Germany had already risen to 13.2 per cent. The statutory target set out in the Renewable Energies Heat Act – to raise this share to above 14 per cent by 2020 – might therefore even be exceeded. By way of comparison, in 2000, the figure was around just 4 per cent.
Transforming heat generation: Good for the climate, easier on the wallet
There are good reasons why home-owners should switch to systems based on renewables and focus on raising energy efficiency. Not only will they save money, but their living comfort will also improve – as will the value of their property. The climate will thank them for their efforts, as well.
The government is providing support for home-owners seeking to make such changes. Anyone who decides to swap their old heating system for a new one powered by green energy is eligible for a government cash grant from the Federal Office for Economic Affairs and Export Control, as part of its Market Incentive Programme. Those who install a heat pump that uses geothermal energy will receive a grant of at least 4,000 euros.