Geothermal energy refers to the thermal energy stored in the accessible part of the earth’s crust and its utilization for heating purposes or electricity generation.
When it comes to renewable energy, we often talk about wind or solar power. An energy resource that is often forgotten or even criticized is geothermal energy. Yet, power and heat generation from geothermal energy, together with other renewable energies, represents an environmentally and climate-friendly alternative to fossil energy, which already avoids greenhouse gas emissions today and will be an essential source for a greenhouse gas-neutral heat supply in the future (Umweltbundesamt). In the earth’s crust, which is on average 30 kilometers thick under continents, the temperature increases by about 3 degrees Celsius per 100 meters (bmwi). The temperature in the liquid outer core of our planet is over 5,000 degrees Celsius. This energy stored in the form of heat beneath the surface of the solid earth is known as geothermal energy. Since this heat is always radiated uniformly in the earth’s interior, its energetic potential is ideal for heating or generating electricity (EEK.SH).
Power and heat generation from geothermal energy, together with other renewable energies, represents an environmentally and climate-friendly alternative to fossil energy, which already avoids greenhouse gas emissions today and will be an essential source for a greenhouse gas-neutral heat supply in the future.
Geothermal energy can be used for heating, cooling and power generation. In Germany, the temperature in the earth’s crust rises by an average of 3 Kelvin per 100 meters; accordingly, near-surface and deep geothermal areas tap different temperature levels (Umweltbundesamt).
Near-surface geothermal energy
Near-surface geothermal energy is the use of geothermal energy from depths of up to 400 meters. Due to the still relatively low temperature, this geothermal heat is usually raised to a usable temperature level with the help of heat pumps, geothermal probes, geothermal collectors or shallow groundwater wells. This form of geothermal use is possible for single-family homes, road construction and subway railroads, as well as for larger commercial or office complexes, e.g. with well galleries or geothermal probe fields. In addition to the use for heating purposes, these near-surface geothermal sources can also be used as a source for cooling purposes in the summer. Across Germany, there are now over four hundred thousand systems for the use of near-surface geothermal energy, with around 20,000 new systems installed every year (Umweltbundesamt; Erdwerk; Lexikon der Nachhaltigkeit).
Deep geothermal energy
Deep geothermal energy operates on a different scale than near-surface geothermal energy: Not only are heat reservoirs tapped at greater depths, with boreholes drilled to depths of up to five kilometers, but the plants operated with them are also much larger and more powerful. In this way, heating networks and entire city districts can be supplied with heating energy. If the temperature level is high enough, a geothermal power plant can also generate electricity (Umweltbundesamt).
The example of Iceland shows how geothermal energy can be used in an environmentally friendly and cost-effective way: More than 30 active volcanoes, plus geysers and hot springs, are visible signs of Iceland’s enormous geothermal potential. 90 percent of all households can be supplied with heat via hot steam, 25 percent of the country’s electricity can be generated with geothermal energy, and 66 percent of all energy consumed in the country can be generated by geothermal energy. In this way, Iceland aims to make itself independent of fossil fuels and imports in its energy supply (planet wissen; Greenpeace).
In Germany, the precondition for heating with geothermal energy is a well-insulated building. The investment costs are comparatively high, between 10,000 and 25,000 euros depending on the complexity, but apart from low maintenance costs and drive power for the heat pump, all running costs can be cut. Heating with geothermal energy amortizes the cost of fossil fuels in eight to twelve years. The average operating costs, including maintenance and electricity requirements, are about thirty percent of comparable gas or oil heating systems – keeping in mind the price increases of fossil fuels in the future (Kesselheld). In addition, geothermal plants for electricity generation are subsidized by the German government through the Renewable Energy Sources Act and the market incentive program (bmwi).
Other advantages are that geothermal energy guarantees an environmentally friendly, seasonal and weather-independent supply of energy inexhaustible and at any time. The area required by a geothermal power plant or heating center is comparatively small and thus space-saving for the end user, as well as being price-stable, safe and odorless. For the municipality, the independence from conventional energy sources, the creation of an affordable and price-stable heat supply through funding opportunities, the increase in local attractiveness and the fulfillment of environmental protection goals are significant advantages (Erdwerk).
Of course, there are also disadvantages, such as the risk of local earthquakes, if the temperature level required for the respective purpose is only given in deeper layers of the earth and deep boreholes into the earth’s interior are necessary. Also criticized is the insertion of heat probes or surface collectors into the ground, which requires a relatively large amount of space that is often not available (Lexikon der Nachhaltigkeit).
However, deep geothermal energy in particular can make a contribution to sustainable energy supply at present and in the future. Environmental effects are locally limited and technically controllable. It represents an inexhaustible energy source by human standards, which, with the right technology, could represent a revolutionary alternative to renewable energies in the future.
by Marie Klimczak