Geothermal energy

Geothermal energy is a forwarding to this article. See also: Earth's interior heat .

Geothermal energy is the heat stored in the accessible part of the earth's crust ( thermal energy ); it can come from the interior of the earth or (for example in frosty soil ) have been brought in through precipitation or melt water and is one of the regenerative energies that can be extracted and used by geothermal heat exchangers. Geothermal energy can be used for heating, for cooling (see ice storage heat pump ), for generating electricity or in the combined cogeneration . Heat " temporarily stored " in an earth buffer storage tank is not counted as geothermal heat.

Geothermal energy describes both the geoscientific investigation of the thermal situation and the engineering use of geothermal energy.

Geothermal energy

origin

Geothermal plant in California

Geothermal power plant in Iceland

Derrick in Bavaria

The glowing earth when it was formed solidified within a few million years. For over four billion years, the radial temperature profile in the Earth's mantle has been only slightly steeper than the adiabatic . At around 1 K / km, this temperature gradient is much too small for heat conduction to make a significant contribution to heat transport. Rather, the amount of temperature gradient exceeding the adiabats drives the jacket convection . The convection, which is very fast compared to the age of the earth - the oceanic crust was and is rarely older than 100 million years - would soon have come to a standstill without active heat sources in the earth's interior. This means that sensible heat from the time the earth was formed is hardly involved in today's heat flow.

The temperature curve over time was initially dominated by the kinetics of radioactive decay. Short-lived nuclides caused the mantle temperature to reach a maximum in the Middle Archean . Since earlier times, heat of crystallization from the boundary of the slowly growing, solid inner earth core and gravitational binding energy from the associated shrinkage of the entire core have contributed to mantle convection.

Today still comes the greater part of the heat power from the radioactive decay of longer-lived nuclides in the jacket, ²³⁵ U and ²³⁸ U, ²³² Th and ⁴⁰ K . The contribution of each nuclide is calculated from the decay energy and the decay rate; this in turn from the half-life and the concentration . Concentrations in the mantle cannot be measured, but are estimated from models of rock formation. The output from radioactive decay is around 20 to 30  terawatts or 40 to 50 kW / km². The total geothermal heat flow from radioactive decay processes is around 900 E J per year. This in turn corresponds to an output of around 27.5 terawatts for the entire earth. Recently decay rates have also been measured directly using neutrino detectors, in agreement with the known result, but still very imprecise, ± 40%.

Heat flow from the interior of the earth

The vertical heat transport through mantle convection ends under the earth's crust . From there, most of the heat is transported by conduction, which requires a much higher temperature gradient than in the mantle, in the continental crust often in the order of 30 K / km, see geothermal depth . The local heat flux density results together with the thermal conductivity . This is on average around 65 mW / m² in the continental area and 101 mW / m² in the ocean area, globally averaged 87 mW / m², which results in a globally integrated heat output of about 44 terawatts.

That is only about twice the global energy demand , which means that the use of geothermal energy on a large scale always results in local cooling of the rock. Due to the thermal capacity of the rock and the associated amount of stored heat, if the volume is sufficiently large, the cooling within the useful life can remain low and the use of geothermal energy can therefore be sustainable. The world energy demand is small compared to the heat stored in the crust. This local cooling in turn then causes the inflow area to be enlarged. In the case of existing aquifers , the volume effectively used can be larger from the outset, since the pressure gradients also play a role here in addition to the temperature gradients. These can be found, for example, in rift valleys (in Germany the Upper Rhine Rift ) or in deep sedimentary basins . Such areas are initially preferable to areas in which a dense rock must first be developed for convection. Due to their high thermal conductivity, heat can flow in from a large volume in the vicinity of salt diapirs .

In the near-surface groundwater and in the near-surface rock layers, the proportion of geothermal energy that ultimately comes from solar radiation increases with decreasing depths.

Classification of geothermal sources

Deep geothermal energy

Deep geothermal energy is the use of deposits that are developed at depths greater than 400 m below the surface level.

The higher the temperature level at which it is available, the more valuable it is. A distinction is made between high enthalpy (high temperatures) and low enthalpy deposits (lower temperatures). A temperature of 200 ° C is usually specified as the limit.

High enthalpy deposits

country	Number of volcanoes	theoretical continuous output
United States	133	23,000 MW el
Japan	101	20,000 MW el
Indonesia	126	16,000 MW el
Philippines	53	6,000 MW el
Mexico	35	6,000 MW el
Iceland	33	5,800 MW el
New Zealand	19th	3,650 MW el
Italy (Tuscany)	3	700 MW el
(Source:)

The global generation of electricity from geothermal energy is dominated by the use of high- enthalpy deposits that provide heat at high temperatures. These are geological heat anomalies that are often associated with active magmatism ; fluids (water / steam) at several hundred degrees Celsius can be found there at a depth of a few hundred meters. Their occurrence correlates strongly with active or previously active volcanic regions. But there are also high enthalpy fields that have a purely plutonic or structural geological background.

Depending on the pressure and temperature conditions, high enthalpy deposits can be more steam or more water dominated. Previously, the steam was released into the air after use, which could lead to a significant sulfur compound odor (Italy, Larderello ). Today the cooled fluids are reinjected (pumped back) into the deposit. This avoids negative environmental impacts and at the same time improves productivity by maintaining a higher pressure level in the deposit.

The hot fluid can be used to provide industrial steam and to feed local and district heating networks. The generation of electricity from the hot steam is particularly interesting. For this purpose, the water heated underground is used to drive a steam turbine. The closed circuit in the circulation system is so pressurized that the injected water is prevented from boiling and the steam is only generated at the turbine ( flash evaporation ).

Low enthalpy deposits

In non-volcanic areas, the underground temperatures can be very different. As a rule, however, deep holes are necessary; Temperatures above 80 ° C are required to generate electricity. For an economically sensible use in Germany, the temperature of the fluid must be above 100 ° C.

In general, a distinction is made between three types of heat extraction from the underground in the area of ​​deep geothermal energy; Which of the processes in question is used depends on the respective geological conditions, the amount of energy required and the required temperature level of heat utilization. It is used more often to generate heat, because economic efficiency can already be achieved with lower flow temperatures. Currently (2010) almost exclusively hydrothermal systems are planned in Germany. HDR processes are currently being tested in pilot projects in Bad Urach  (D), in Soultz-sous-Forêts in Alsace (F) and in Basel  (CH). A commercial project has been underway in Southeast Australia's Cooper Basin since 2001 ( Geodynamics Limited ).

Hydrothermal systems

If the corresponding temperatures are present in an aquifer , water can be pumped, cooled and reinjected from this: Thermal water present in the subsurface is pumped at one point and injected into the same natural aquifer at another point. A pressure equalization is sufficient for the promotion, the thermal water itself does not circulate underground. Depending on the prevailing temperature, hydrothermal energy can be used to generate heat or electricity. The geological horizons that can be used for hydrothermal geothermal energy in Germany can be seen in the geothermal information system.

Petrothermal Systems

The principle of using geothermal energy from hot dense rock (HDR)

are often referred to as HDR systems ( H TDC D RY R denotes ock): If the rock in which the high temperatures encountered little permeable , so that water can be conveyed out of it, so there may be an artificially introduced heat transfer medium (water or CO ₂ ) between two deep are circulated wells in an artificially generated crack system initially water is (a minimum) injection or Verpressbohrung pressed into the fracture system which under a pressure sufficiently above the petrochemical static pressure must lie that the minimum main stress in the respective depth is exceeded, pressed into the rock ( hydraulic stimulation or fracking ); as a result, flow paths are broken up or existing ones widened, thus increasing the permeability of the rock. This procedure is necessary because otherwise the heat transfer area and the patency would be too small. This system then forms an underground geothermal heat exchanger from natural and artificial cracks . Through the second, the production or production well , the carrier medium is conveyed back to the surface.

In fact, the assumption that dry rock formations will be found at these temperatures and depths is incorrect. For this reason there are various other names for this process: u. a. Hot-Wet-Rock (HWR), Hot-Fractured-Rock (HFR) or Enhanced Geothermal System (EGS). The term petrothermal systems is used as a neutral term .

Deep geothermal probes

→ Main article : Geothermal probe

A deep geothermal probe is a closed system for geothermal heat recovery, in which comparatively little energy is extracted compared to "open" systems. The probes consist of a single borehole, some of which are significantly more than 1000 m deep, in which a fluid circulates that is usually enclosed in a coaxial tube. In the annular space of the bore, the cold heat transfer fluid flows downwards, is heated in the depth and then rises again in the thinner, suspended riser . With such geothermal probes there is no contact with the groundwater, so the disadvantages of open systems are eliminated and they can be used at any location. In addition to technical parameters, their extraction performance depends on the mountain temperatures and the conductivity of the rock. However, it will only be a few hundred kW and thus be significantly smaller than that of a comparable open system. This is due to the fact that the heat transfer surface is significantly smaller, since it only corresponds to the outer surface of the bore.

For example, deep geothermal probes were built in 2005 in Aachen ( SuperC of RWTH Aachen University ) and Arnsberg ( water park Nass ). At the end of 2009, the Tiefen-EWS Oftringen research facility was implemented in Switzerland. This is a 706 m deep conventional double U-probe, which was tested in 2009/2010 in terms of direct heating (i.e. without the use of a heat pump).

Alternatively, for circulating water (with any additives) in the geothermal probe and probes (with direct evaporators are heat pipes English or heat pipes ) have been proposed. Either a liquid with a correspondingly low boiling point or a mixture of water and ammonia, for example, can be used as the heat transfer fluid . Such a probe can also be operated under pressure, which enables operation with carbon dioxide, for example . Heat pipes can achieve a higher extraction capacity than conventional probes, since they can have the evaporation temperature of the working medium over their entire length.

In the case of deep geothermal probes up to 3000 m, insulation up to a depth of about 1000 m is useful in order to reduce losses of thermal energy when the fluid ascends through colder rock layers. This enables a higher energy yield or the same performance can be achieved with significantly lower costs with a smaller drilling depth. A permanent option for insulation, which can also be produced relatively easily, is the insulation cap system that works with air cushions .

Near-surface geothermal energy

Near-surface geothermal energy refers to the use of geothermal energy up to a depth of approx. 400 m.

From a geological point of view, every piece of land is suitable for use of geothermal energy. However, economic, technical and legal aspects must be taken into account.

The required geothermal heat exchanger must be dimensioned appropriately for each building. It depends on the required amount of heat , thermal conductivity and the groundwater flow of the subsoil.

The costs of a system depend on the required size of the system (for example geothermal probe meters). These are calculated from the house's energy requirements and the geological subsurface conditions.

Geothermal energy use must be reported to the water authority. In the case of geothermal energy that spans land and drilling depths of more than 100 m (depending on the [federal state]), the mining and storage site law must be observed.

The geothermal energy is used by means of geothermal collectors , geothermal probes , energy piles ( reinforced concrete supports built into the ground with plastic pipes for heat exchange) or a thermal well system (stored solar heat in the ground).

The geothermal heat is transported via pipeline systems with a circulating liquid, which is usually connected to a heat pump. The system described can also be used inexpensively (without a heat pump) for cooling.

Geothermal energy from tunnels

Exiting tunnel water is also used to generate thermal energy from tunnel structures , which otherwise would have to be temporarily stored in cooling basins for environmental reasons before it can be discharged into local waters. The first such known system was put into operation in 1979 in Switzerland at the south portal of the Gotthard road tunnel . It supplies the Airolo motorway depot with heating and cooling. In the meantime, additional systems have been added, which mainly use hot water from rail tunnels . At the north portal of the Gotthard Base Tunnel , which is currently under construction , tunnel water with temperatures between 30 and 34 ° C is already emerging. It will soon be used in a district heating network. The tunnel water from the new Lötschberg railway tunnel is used for sturgeon breeding and for a tropical house .

In Austria a process was developed to use the heat from tunnels by means of a transport medium that circulates in walled-in collectors . For conventionally driven tunnels, the principle became known as TunnelThermie . Due to the large areas in contact with the ground, this relatively young technology has a high potential for use, especially in inner-city tunnels.

In Germany , a process was developed to use geothermal energy in machine-driven tunnels. For this purpose, collectors are built into precast concrete parts (so-called segments ), which form the shell of a tunnel (known as energy segments ). Since inner-city tunnels are often driven with shield driving in difficult geological conditions , the energy segment offers the possibility of using the geothermal potential of the ground along these routes.

Geothermal energy from mining plants

Mines and depleted natural gas reservoirs that are shut down due to depletion of supplies are conceivable projects for deep geothermal energy. This also applies to a limited extent to deep tunnels. The formation waters there are 60 to 120 ° C, depending on the depth of the reservoir, the boreholes or shafts are often still available and could be reused to feed the warm reservoir waters for geothermal use.

Such systems for the generation of geothermal energy must be integrated into the facilities for the safekeeping of the mine in such a way that the publicly standardized safekeeping goals to keep the decommissioned mine (Section 55 (2) Federal Mining Act and Section 69 (2) Federal Mining Act) safe, including additional facilities are met.

There are pilot plants in Heerlen , Czeladź , Zagorje ob Savi , Burgas , Novoschachtinsk in Russia and Hunosa near Oviedo .

Seasonal heat storage

Geothermal energy is always available, regardless of the time of day and season and regardless of the weather. A system in which the temperature level close to the surface is to be used will work optimally if it is also used homogeneously over time . This is the case, for example, when the near-surface temperature level of approx. 10 ° C is used for heating in winter with the help of a heat pump and is reduced accordingly and this reservoir is then used for direct cooling in summer. When cooling in summer, the near-surface reservoir is heated and thus partially or completely regenerated. Ideally, both amounts of energy are the same. The energy consumption of the system then essentially consists of the drive power for the heat or circulation pump.

This function is reinforced when geothermal energy is combined with other systems, for example solar thermal energy . Solar thermal provides heat mainly in summer when it is less needed. By combining it with geothermal energy, this energy can be fed into the underground heat storage in summer and retrieved again in winter. The losses depend on the location, but are usually small.

Seasonal storage can be carried out both near the surface and deep. So-called high temperature storage tanks (> 50 ° C) are only conceivable at greater depths or with appropriate insulation. For example, the Reichstag building has such a storage facility.

Use of geothermal energy

From a global perspective, geothermal energy is a long-term energy source. With the supplies that are stored in the upper three kilometers of the earth's crust, the current global energy demand could in principle be met arithmetically and theoretically for over 100,000 years. However, only a small part of this energy is technically usable and the effects on the earth's crust in the event of extensive heat degradation are still unclear.

When using geothermal energy, a distinction is made between direct use , i.e. the use of the heat itself, and indirect use , the use after conversion into electricity in a geothermal power plant. With some restrictions, combined heat and power (CHP) are also possible here to optimize efficiency . CHP processes are particularly difficult to implement in sparsely populated areas or at power plant locations that are far away from settlements with heating requirements. Customers for the heat will not be found at every power plant location.

Direct use

required temperature level for different uses, Lindal diagram

Type of use	temperature
Boiling down and evaporation, seawater desalination	120 ° C
Drying cement boards	110 ° C
Drying of organic material such as hay, vegetables, wool	100 ° C
Air drying of stockfish	90 ° C
Heating water temperature for space heating (classic)	80 ° C
cooling	70 ° C
Animal breeding	60 ° C
Mushroom cultivation, balneology, used hot water	50 ° C
Underfloor heating	40 ° C
Swimming pools, keeping ice free, biological decomposition, fermentation	30 ° C
Fish farming	20 ° C
Natural cooling	<10 ° C

Early balneological applications can be found in the baths of the Roman Empire , the Middle Kingdom of the Chinese, and the Ottomans.

In Chaudes-Aigues in central France there is the first historical geothermal district heating network, the beginnings of which go back to the 14th century.

Today there are many uses for thermal energy in industry, trade and in residential buildings.

Heating and cooling with geothermal energy

For most applications only relatively low temperatures are required. The required temperatures can often be made available directly from deep geothermal energy . If this is not enough, the temperature can be raised by heat pumps , as is usually done with near-surface geothermal energy .

In connection with heat pumps, geothermal energy is usually used for heating and cooling buildings and for hot water preparation. This can be done directly via heat pump heating systems installed in individual buildings or indirectly via cold local heating systems , in which the geothermal source feeds the cold heating network , which in turn supplies the individual buildings.

Another possible use is natural cooling , in which water at the temperature of the flat subsurface, i.e. the annual mean temperature of the location, is used directly to cool the building (without the use of a heat pump). This natural cooling has the potential to replace millions of electrically operated air conditioning units worldwide. However, it is currently rarely used. In November 2017 the data center ColocationIX-Data-Center went into operation in Bremen, which draws cooling from geothermal energy during the summer months.

Another direct application is keeping bridges, roads or airports free of ice . Here, too, no heat pump is required, because the storage tank is regenerated in summer by removing and storing the heat from the hot road surface with a circulation pump. This also includes the frost-free laying of water pipes. The heat contained in the soil allows the soil in Central Europe to freeze only to a shallow depth in winter.

For the use of heat from deep geothermal energy , low-thermal deep waters with temperatures between 40 and 150 ° C, such as those found above all in the southern German Molasse basin , in the Upper Rhine Rift and in parts of the northern German lowlands, are suitable . The thermal water is usually brought to the surface from a depth of 1000 to 4500 meters via a production well and transfers the major part of its thermal energy to a second, "secondary" heating network circuit via a heat exchanger. Once it has cooled down, it is then pumped back into the subsurface via a second bore, namely into the layer from which it was taken.

Power generation

Direct use of geothermal energy worldwide
(status: 2010, source: literature / statistics, 7.)

Type of use	Energy [TJ / a]	Power output capacity [MW]
Heat pumps	214.236	35,236
Swimming pools	109.032	6,689
Space heating / district heating	62,984	5,391
Greenhouses	23,264	1,544
Industry	11,746	533
Aquaculture	11,521	653
Drying (agriculture)	1,662	127
Cooling, melting snow	2.126	368
Other usage	956	41
Total	438.077	50,583

Electricity generation works according to the principle of heat engines and is limited by the temperature difference. That is why geothermal power plants have a low Carnot factor compared to combustion power plants, but in some places they are almost inexhaustible.

Geothermal energy was first used to generate electricity in Larderello in Tuscany. In 1913, Count Piero Ginori Conti built a power station there in which steam-powered turbines generated 220 kW of electrical power. Today around 750 MW of electrical power are installed there. Under Tuscany, magma is relatively close to the surface. This hot magma increases the temperature of the ground so much that the geothermal energy can be used economically.

When generating hydrothermal electricity, water temperatures of at least 80 ° C are necessary. Hydrothermal hot and dry steam deposits with temperatures above 150 ° C can be used directly to drive a turbine, but these do not occur in Germany.

Scheme drawing for electricity generation from geothermal energy

For a long time, thermal water was therefore used exclusively to supply heat to buildings. Newly developed organic Rankine cycle systems (ORC) enable temperatures from 80 ° C to be used to generate electricity. These work with an organic medium ( e.g. pentane ) that evaporates at relatively low temperatures. This organic steam drives the electricity generator via a turbine. Some of the fluids used for the cycle are flammable or toxic. Regulations for handling these substances must be observed. An alternative to the ORC process is the Kalina process . Here are binary mixtures , for example, ammonia , and water used as a tool.

For systems in a smaller power range (<200 kW), motor drives such as Stirling engines are also conceivable.

Electricity generation from deep geothermal energy is base- load capable and controllable; in existing systems, more than 8,000 operating hours are often achieved per year.

Electricity generation via Hochenthal play facilities

Electricity generation from geothermal energy traditionally takes place in countries that have high enthalpy deposits where temperatures of several hundred degrees Celsius are encountered at relatively shallow depths (<2000 m). Depending on the pressure and temperature, the deposits can be dominated by water or steam. With modern conveying techniques, the cooled fluids are re-injected so that there are practically no negative environmental impacts, such as the smell of sulfur compounds.

Electricity generation via Niederenthal play storage facilities

In low-level playgrounds , as they are mostly found in Germany, the maximum possible energetic efficiency is lower than in high-level playgrounds due to the low temperature difference between flow and return .

By optimally choosing the working medium ( e.g. Kalina process with ammonia) one tries to use the distance between the flow and return temperature more efficiently. It should be noted, however, that the safety requirements for handling ammonia can be different from those for using various organic working materials.

The self-consumption of electricity, especially for feeding the circulation pumps in the thermal water circuit, in such systems can amount to up to 25 percent of the amount of electricity generated.

Geothermal energy worldwide

Geothermal energy is an important renewable energy. The countries that have Hochenthal play facilities make a special contribution to their use. There, the share of geothermal energy in the total energy supply of the country can be significant, for example geothermal energy in Iceland .

Direct use

country	Energy turnover per year	Annual mean power output
China	45,373 TJ	1.44 GW
Sweden	36,000 TJ	1.14 GW
United States	31,239 TJ	0.99 GW
Iceland	23,813 TJ	0.76 GW
Turkey	19,623 TJ	0.62 GW
Hungary	7,940 TJ	0.25 GW
Italy	7,554 TJ	0.24 GW
New Zealand	7,086 TJ	0.22 GW
Brazil	6,622 TJ	0.21 GW
Georgia	6,307 TJ	0.20 GW
Russia	6,243 TJ	0.20 GW
France	5,196 TJ	0.16 GW
Japan	5,161 TJ	0.16 GW
total	208,157 TJ	6.60 GW
Source: Schellschmidt 2005

In 2005, plants with a capacity of 27,842 MW were installed worldwide for the direct use of geothermal energy. These can deliver energy in the order of 261,418 TJ / a (72,616 GWh / a), which corresponds to an average power output of 8.29 GW or 0.061% of the world's primary energy consumption . With a world population of 6.465 billion people in 2005, each person consumed 1.28 watts (who consumed an average of 2,100 watts of primary energy). The utilization rate of the installed capacity is about 30% (this figure is important for the rough calculation of the profitability of planned systems, but it is largely determined by the consumer structure and less by the producer, i.e. the heat source).

The table shows countries with energy sales greater than 5000 TJ / a.

Particularly noteworthy are Sweden and Iceland. Sweden tends to be geologically disadvantaged, but has achieved this high proportion of the use of renewable energies primarily for heating (heat pump heating) through consistent policy and public relations work.

In Iceland, too, the use of this energy makes up a considerable proportion of the country's energy supply (approx. 53%), cf. Geothermal energy in Iceland . It is now a global pioneer in this field.

The geothermal power plant Olkaria (121 MW, potential 2 GW) in the African Rift Valley , which went into operation in 1981 and is constantly being expanded , now covers 14% of Kenya's nationwide electricity needs . The successes led to geothermal projects in Eritrea , Uganda , Tanzania and Ethiopia , which are also located along the East African Rift Valley.

In the Middle East , the first geothermal project is being implemented in the United Arab Emirates . It is intended to supply the eco-city of Masdar with energy for cooling purposes. Initially, two test wells were started at depths of 2800 m and 4500 m.

Power generation

Electricity generation from geothermal energy has traditionally been concentrated in countries that have near-surface high-enthalpy deposits (mostly volcanic or hot-spot areas ). In countries that do not have this - such as Germany, for example - the electricity must be generated at a comparatively low temperature level (Niederenthal play area with around 100–150 ° C), or the drilling must be correspondingly deeper.

There has been a global boom in the use of geothermal energy to generate electricity. The installed capacity at the end of the first quarter of 2010 was 10,715 MW. This means that 56 67,246 GWh / a of base-load electrical energy is provided in the 526 geothermal power plants worldwide.

In the past five years, electricity generation has expanded significantly. In relation to some countries, the increases indicated in the table on the left result for the period 2005–2010.

Country (selection)	2005–2010 newly installed electrical output MW e
United States	529
Indonesia	400
Iceland	373
New Zealand	193
Turkey	62
El Salvador	53
Italy	52
Kenya	38
Guatemala	19th
Germany	6th
(Source:)

Right table - countries with a significant share of geothermal energy in the total supply (as of 2005):

country	Share of electricity generation in%	Share in the heating market in%
Tibet	30th	30th
San Miguel Island	25th	no information
El Salvador	14th	24
Iceland	19.1	90
Philippines	12.7	19.1
Nicaragua	11.2	9.8
Kenya	11.2	19.2
Lihir Island	10.9	no information
Guadeloupe	9	9
Costa Rica	8.4	15th
New Zealand	5.5	7.1
(Source:)

So far, low-enthalpy deposits have been little used worldwide. They could gain in importance in the future, as this use is more widespread and does not require special geothermal conditions with above-average geothermal gradients. In November 2003, the first such power plant in Germany, the Neustadt-Glewe geothermal power plant , with an output of 0.23 megawatts, went into operation. The first industrial installation followed in 2007 with the 3 megawatt system of the Landau geothermal power plant .

In Australia , the first purely economical geothermal power plant based on HFR (Hot Fractured Rock) is being built in Cooper Basin . So far, two holes have been drilled to a depth of more than 4000 m and an artificial crack system has been created. At 270 degrees, the temperatures are higher than expected and the artificially created water path between the wells is better than planned.

In terms of the per capita use of geothermal energy, Iceland is currently the front runner with 664 MW (2011) installed total capacity ( geothermal energy in Iceland ). The USA, on the other hand, leads the absolute values ​​with a total installed capacity of 3093 MW (2010), followed by the Philippines with 1904 MW (2010) and Indonesia with 1197 MW (2010). (Source:)

Situation in Germany

The inside of the former geothermal power plant Neustadt-Glewe in Germany

According to German mining law ( Federal Mining Act, BBergG, Section 3 Paragraph 3 Clause 2 No. 2b), geothermal energy is a non-mined raw material ( mined natural resource ). It is therefore initially considered ownerless, with the respective applicants gaining the right to search and use by granting it from the state (if it is not used for urban development purposes, because then the definition of extraction in Section 4 (2) of the Federal Mining Act is not relevant). This means that ownership of a property does not extend to geothermal energy. For the exploration of geothermal energy a permit according to § 7 BBergG is required and for obtaining a permit according to § 8 BBergG. Most of the near-surface geothermal systems can, however, so far be built according to § 4 BBergG without such a procedure if the use takes place on one's own property ; the exact delimitation depends on the respective state law. In any case, systems that reach into the groundwater require a permit under water law . For boreholes that are longer than 100 meters, an operating plan under mining law is also required. The city of Freiburg im Breisgau has, however, tightened its requirements for near-surface geothermal projects for boreholes below 100 m, among other things as a result of the terrain elevations that occurred in Staufen after a test drilling and the earthquake triggered in Basel .

The geothermal power generation is in Germany still in its infancy. Among other things (status: 2009) the German Research Center for Geosciences in Potsdam is working intensively on this topic. The Lower Saxony research association “Geothermal Energy and High Performance Drilling Technology - gebo” pursued the goal of developing new concepts for geothermal energy generation in deep geological layers from 2009 to 2014. In addition, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) supports numerous research projects to increase the efficiency of deep geothermal energy. In Bad Urach (Swabian Alb), a longstanding and well advanced HDR research project could not be completed for financial reasons. Instead, the boreholes are now to be used from the shell limestone thermal water to heat buildings.

Eleven power plants (in southern Bavaria: Sauerlach , Taufkirchen , Laufzorn , Kirchstockach and Dürrnhaar near Munich, Holzkirchen , Traunreut , Simbach - Braunau ; in the Upper Rhine Graben : Bruchsal , Landau in the Palatinate and Insheim ) currently generate electricity from deep geothermal energy in Germany (as of December 2019).

Some other projects are under construction or almost completed, so that an increase in the share of geothermally generated electricity can be expected in the next few years.

In contrast, the direct energetic use of hydrothermal geothermal energy in the operation of heating networks is very widespread . An overview of the existing hydrogeothermal facilities in Germany can be found in the directory of geothermal locations.

In Germany, the direct use of near-surface geothermal energy (heat pump heating) is already widespread, and in 2010 51,000 new systems were installed. A total of around 330,000 systems were installed in 2009. For the first time, extensive research is to be carried out on the use of near-surface geothermal energy in the geothermal park in Neuweiler in the northern Black Forest; a building area in which only geothermal energy is used to heat and cool buildings. As part of a model project, the heating and cooling of the existing roads are to be implemented for the first time. Near-surface geothermal energy is also used in Bavaria a. a. investigated in the vicinity of Ansbach , where there is also a training focus at the local technical college.

According to the figures from the BMU for 2004, the following picture emerged for Germany: The energy generation in 2004 from geothermal energy of 5609 TJ / a (corresponding to an average output of 0.178 GW in 2004) resulted in primary energy consumption in Germany in the same year of 14,438,000 TJ / a (corresponding to an average output of 458 GW). In 2004, 0.04% of primary energy consumption in Germany was covered by geothermal energy. For 2005, the industry anticipated sales of around 170 million euros and investments of 110 million euros. Around 10,000 people already worked directly or indirectly for geothermal energy supply (source, see literature / statistics, 2.).

Direct use

In the area of ​​deep geothermal energy there are currently (as of 2005) 30 installations with outputs of over 2 MW in Germany. Together they provide 105 MW (source, see literature / statistics, 4.). Most of these facilities are in the

• North German Basin,
• South German Molasse Basin or in the
• Upper Rhine Plain / Upper Rhine Graben.

Due to geological reasons, the north of Germany has a great potential of geothermally usable energy in thermal water-bearing pore storage of the Mesozoic era at a depth of 1000 to 2500 m with temperatures between 50 ° C and 100 ° C. The geothermal heating center (GHZ) in Neubrandenburg was already one of the pilot projects for the use of geothermal energy in the GDR.

The Molasse basin in southern Germany (Alpine foothills) offers favorable conditions for deep geothermal use. Numerous balneological developments in Baden-Württemberg (Upper Swabia) and Bavaria ( spa triangle ) have existed for several decades. In addition, there were around twenty large energetic uses in southern Bavaria in 2019 (geothermally operated district heating networks in Simbach-Braunau , Straubing, Erding , Unterschleißheim, Pullach, Munich-Riem , Unterhaching, Unterföhring, Aschheim-Feldkirchen-Kirchheim, Ismaning, Munich-Freiham , Waldkraiburg, Poing, Garching, Grünwald, Traunreut, Sauerlach, Taufkirchen, Kirchweidach, Holzkirchen) and numerous others are in planning or under construction (e.g. Munich-Sendling). The thermal water comes from a limestone layer (pore, crevice and karst groundwater ) of the Upper Jura (Malm) at the base of the north Alpine molasse trough. These rocks appear on the surface of the earth along the Danube and descend towards the south on the edge of the Alps to over 5000 m below the surface. Temperatures higher than 140 ° C are also to be expected there.

The Upper Rhine Graben offers particularly good geological and geothermal conditions throughout Germany (including high temperature, heat flow, structure in the subsoil). However, the thermal waters in the Upper Rhine Graben are rich in dissolved ingredients, which places high demands on the system technology. Projects are in operation, in planning and under construction at various locations. Concessions have already been granted for many regions.

In North Rhine-Westphalia, for example, it is also being investigated whether mine water can be used thermally.

Just like North Rhine-Westphalia, Baden-Württemberg has launched a funding program for geothermal probe systems for small residential buildings, with funding for drilling meters, see web links.

In addition, there are more than 50,000 near-surface geothermal systems in Germany in which heat pumps are used to raise the temperature. Together these have an output of more than 500 MW. A rather small market share compared to Sweden, Switzerland or Austria. In 2000 it was 2 to 3% in Germany, 95% in Sweden, and 36% in Switzerland (see also heat pump heating ).

Power generation

The first geothermal power plant in Germany was put into operation in 2004 in Mecklenburg-Western Pomerania as an extension of the geothermal heating plant built in 1994. The electrical output of the Neustadt-Glewe geothermal power plant was up to 230 kW. Hot water at around 97 ° C was pumped from a depth of 2250 meters and used to supply electricity and heat. In 2004 the amount of electricity generated was 424,000 kilowatt hours (source: AGEE-Stat / BMU); The electricity generation of this geothermal pioneer power plant was stopped again in 2010. Since then, 11 more geothermal power plants have been built in Germany, and more are currently under construction, most of them on the Upper Rhine and in the Upper Bavarian Molasse Basin . The mining authorities have issued numerous exploration permits for the commercial use of geothermal energy (over 100 by 2007).

The heat reservoirs with high temperatures required for electricity generation are only available at great depths in Germany. Developing the temperatures required for operation is associated with a high financial outlay. Geological and drilling technical development risks must be weighed in relation to the financial expenditure. Research work on the use of deep-lying or largely water-impermeable rocks is ongoing and promises to further increase the possibilities for electricity generation. A study by the German Bundestag indicates the potential for electricity production to be 10 ²¹ joules.

Planned and implemented geothermal systems (heat and electricity generation) in German-speaking countries (D / A / CH)

	Geoth. Power in MW	Electrical output in MW	Temperature in ° C	Delivery rate in m³ / h	Drilling depth in m	(Planned) commissioning year
Germany
Groß Schönebeck research project	10	1.0	150	<50	4,294	Trial operation, currently no electricity generation
Neustadt-Glewe	10	0.21	98	119	2,250	Power plant operation since 2003–2009, power generation stopped in 2009
Bad Urach (HDR pilot project)	6-10	approx. 1.0	170	48	4,500	Project finally canceled in 2004 due to Financing / drilling tech. Problems
Bruchsal	4.0	approx. 0.5	118	86	2,500	In power plant operation since 2009
Landau in the Palatinate	22nd	3	159	70	3,000	Trial operation since 2007. Temporarily suspended due to slight earthquakes. Resumption with reduced pump pressure.
Insheim		4-5	> 155		3,600	Power plant operation since November 2012
Bruehl	40	5-6	150		3,800	(Drilling work currently interrupted due to lawsuit; lawsuit dismissed), GT1 successfully tested. Borehole abandoned and discontinued due to bankruptcy.
Schaidt			> 155		> 3,500	The mining approvals granted in 2010 have expired. The future is open.
Offenbach on the Queich	30-45	4.8-6.0	160	360	3,500	stopped due to Borehole instability
Speyer	24-50	4.8-6.0	150	450	2,900	Abandoned in 2005 because oil was found instead of water (three wells in trial operation)
Simbach-Braunau	7th	0.2	80	266	1,900	District heating since 2001, ORC power plant in operation since 2009
Unterhaching	40	3.4	122	> 540	3,577	in operation since 2008; Kalina power plant shut down since mid-2017
Sauerlach	about 80	approx. 5	140	> 600	> 5,500	in operation since 2013
Thin hair	approx. 50	approx. 5.0	135	> 400	> 4,000	in operation since 2013
Mauerstetten			120-130	0	4,100	Hole not found.
Kirchstockach	50	5	130	450	> 4,000	in operation since 2013
Laufzorn (Grünwald-Oberhaching)	50	5	130	470	> 4,000	in operation since 2014
Kirchweidach			120	470	> 4,500	Focus on heat for greenhouses & district heating
Pullach i. Isar valley	16		105	> 300	3,443	In operation since 2005, two production wells and one reinjection well, heat-controlled system with 45 km district heating network (as of 2018)
Taufkirchen	35	4.3	136	430	> 3,000	in operation since 2018
Traunreut	12	5.5	120	470	4,500	in operation since 2016
Geretsried			160	0	> 4,500	Drilling finished; Drilling in 2013 found no thermal water; the sidetrack drilled in 2017 also remained dry
Bernried on Lake Starnberg					> 4,500	on standby, start of drilling postponed
Weilheim in Upper Bavaria				0	4,100	Drilling finished; Borehole found no thermal water
Wooden churches	24	3.4	155	200	5,100	District heating since 2018 Power plant since 2019
Groß-Gerau / Trebur			160	0	3,500	Hole not found
Neuried (Baden)		3.8				6 municipalities speak out against the project. Start of drilling postponed due to dismissed complaint; Realization planned as soon as possible. The "Citizens' Initiative Against Deep Geothermal Energy in the Southern Upper Rhine Rift" fights against the project, and the citizens are very opposed to the project.
Icking ( Höhenrain , Dorfen)			140	0	approx. 4,000	Hole not found
Bruck ( Garching an der Alz )	6.2	3.5	120-130		approx. 3,800	Drilling work ended in 2018 and you found what you were looking for
Austria
Altheim (Upper Austria)	18.8	0.5	105	300-360	2.146	In power plant operation since 2000
Bad Blumau	7.6	0.18	107	approx. 80-100	2,843	In power plant operation since 2001
Aspern			150		5,000	Drilling work canceled
France
Soultz-sous-Forêts	12.0	2.1	180	126	5,000	Test operation since 2008
Strasbourg-Vendenheim						Project suspended due to earthquake in December 2019
Strasbourg-Illkirch						Project is suspended due to drilling problems at a depth of 2 km December 2019
Switzerland
Basel			200		5,000	Project suspended due to quake
St. Gallen			150-170		approx. 4,000	Project canceled, high gas ingress and increased seismicity during the production test

State support measures

Renewable Energy Sources Act (EEG)

As a result of the amendment to the EEG (Renewable Energy Sources Act) on January 1, 2012, geothermal electricity generation will receive significantly more subsidies per kilowatt hour than before. The CHP bonus and early starter bonus are integrated into the basic remuneration, so that this increases from 16 to 23 ct / kWh. The basic remuneration is now 25 ct / kWh with an additional increase of 2 ct / kWh. There is also a technology bonus for petro-thermal projects of 5 ct / kWh. This level of remuneration applies to all systems commissioned up to and including 2017. From 2018 onwards, the tariff rates applicable to new systems (corresponding to the times of commissioning) will decrease by 5% annually (degression). So far, this reduction should be 1% annually from 2010. Furthermore, the remuneration of a system remains constant over the remuneration period (20 to almost 21 years). The feed-in tariff is used for the gross electricity production of the plant. This corresponds to a uniform EEG regulation and applies to all forms of renewable electricity generation. The self-energy requirement of German geothermal power plants is approx. 30% of the gross electricity production (the main consumers are the feed pumps).

Market incentive program of the BMU

Deep geothermal systems are funded from the MAP (market incentive program of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety) through low-interest loans with repayment grants. The following are eligible for funding:

• The construction of the deep geothermal system ("system funding")
• The realization of the production and injection wells ("drilling cost subsidies") as well as unforeseen additional costs compared to the drilling planning ("additional expenses")
• The reduction of the exploration risk through exemption from liability for up to 80% of the drilling costs ("exploration risk credit program")
• The establishment of heating networks ("heating networks")

From this, KfW can grant loans per project amounting to up to 80% of the drilling costs. These loans are released from liability in the event of failure. H. they do not have to be repaid by the borrower from this point on. The “KfW Special Program” for general project financing, such as a. Geothermal projects, banks refinanced by means of KfW loans up to a loan amount of i. d. Usually 200 million euros per project.

Due to the high investment costs and exploration risks associated with the drilling, insofar as these exceed the above-mentioned Exemption from liability, there is a relatively high initial barrier to deep geothermal projects. This makes financing difficult. The relatively long project development time and the associated duration of the equity investment make the financing more expensive.

Economic aspects

The low use of geothermal energy, which is available everywhere and is free of charge, is due to the fact that both the heat flow with ≈ 0.06 watt / m² and the temperature increase with depth of ≈ 3 K / 100 m in the accessible parts of the earth's crust from apart from special locations, are so small that it was not economical to use them in times of low energy prices. With the awareness of the CO ₂ problem and the foreseeable shortage of fossil fuels, more geological exploration and technical development of geothermal energy began.

Since the actual energy, geothermal energy, is free, the profitability of geothermal energy use is primarily determined by the investment costs (interest) and maintenance costs of the systems.

Under the current political framework ( Renewable Energy Sources Act ), economic efficiency for larger geothermal systems can also be achieved in Germany in many areas, for example in Upper Bavaria, Upper Rhine Graben and the North German Basin.

In principle, larger geothermal systems (over 0.5 MW and with a depth of more than 500 m) are always associated with certain exploration risks, as the deeper layers of the earth are only explored selectively and often to a limited extent. The temperatures to be found can usually be forecast quite well. However, the bulk quantities that are particularly relevant in hydrothermal systems are often difficult to predict. Lately, however, risk insurance has been offered. The geothermal information system (funded by the BMU ) was created to minimize the exploration risk .

The near-surface use of geothermal energy for heating buildings by means of a heat pump is already competitive in many cases. Heat pump heating systems usually consist of one or more geothermal probe (s) and a heat pump or several connected in parallel. In 2004 around 9,500 new plants were built in Germany, in 2006 there were already 28,000 and the number exceeds 130,000. In 2004 there were around 4,000 new systems using geothermal energy in Switzerland. In contrast to countries like Sweden, Switzerland and Austria, the market share in Germany is still small.

The system's resistance to wear and tear (e.g. moving parts of a heat pump or a Stirling engine ) plays a role in the operating costs . In open systems, corrosion can result from aggressive components in the heat-transporting water (all parts in the earth and the heat exchangers). However, these previously significant problems have largely been technically solved today.

Ecological aspects

Energy potential

Geothermal energy is counted among the regenerative energy sources , as its potential is considered to be very large and inexhaustible from a human perspective. The cumulative energy expenditure (KEA, also: gray energy) of geothermal energy is in the range of 0.12 . In theory, the energy stored in the top three kilometers of the earth's crust alone would be enough to supply the world with energy for around 100,000 years. However, only a very small part of this energy is technically usable. In work report 84 of the Office for Technology Assessment at the German Bundestag , an annual technical supply potential from geothermal "electricity generation of approx. 300 TWh / a for Germany was determined, which corresponds to about half of the current gross electricity generation". The calculations in the study determine a sustainable usage period of one thousand years for this form of 50 percent total geothermal electricity generation. The heat transfer fluid (water or steam) has a decisive influence on the implementation of sustainable use. If the heat is withdrawn from the subsurface on a large scale via the fluid, then, depending on the geological conditions, more heat is regionally withdrawn than can initially "flow in" through the natural heat flow. From this point of view, the heat is first “broken down”. After the end of use, however, the natural temperature conditions will be restored after a certain time. The extraction scenario of the study takes the heat flows into account in the potential calculation. Like biomass or hydropower, geothermal energy can be used for power generation and non-heat-controlled power plants . ${\displaystyle kWh_{PE}/kWh_{th}}$

Regeneration of the heat reservoir

Since in geothermal power plants in regions with a low or average heat flow, more heat energy is extracted from the earth's crust than can naturally flow in, the energy stored in the earth's crust is broken down. The useful life of a power plant or location is therefore limited depending on the rate of energy extracted. However, the heat reservoir regenerates itself after a while due to the natural heat flow. The regeneration of a heat reservoir in the area of ​​cold water injection depends very much on the geological framework conditions. It is important here whether the heat is fed exclusively from below via heat conduction or whether additional heat is fed convectively by transporting warm water.

Regeneration in a cleft system

Heat transport by convection is always more effective, as the problem of limiting heat transport is circumvented by the resistance of the mountain body to heat conduction . Therefore, an investor for geothermal projects should, if possible, look for geological regions in which warm or hot deep water flows through fissures (open fracture systems):

• Karst areas (e.g. the Bavarian Molasse Basin) or
• Zones with open fracture systems (e.g. the Upper Rhine Graben)

are therefore preferred regions in Germany for geothermal projects.

In a model calculation of the heat transport, the following was determined as an example for a location in the Bavarian Molasse Basin: For a hydrothermal system in the Malmkarst with a reinjection rate of 50 l / s and a reinjection temperature of 55 ° C, the following period of time for complete heat regeneration immediately around the injection well Calculated after the completion of the duplicate operation with purely conductive heat transport: After 2,000 years a temperature of 97 ° C and about 8,000 years after the end of operation the starting temperature of 99.3 ° C is reached again: "The modeling of the heat regeneration after the end of a 50-year operating period under The given boundary conditions make it clear that extensive thermal regeneration of the reservoir in the Malm can be expected after 2000 years at the earliest ”. The model calculation also illustrates the high potential of the reservoir: “In the present scenario, it can be said in summary that over the operating period of 50 years, as expected, only a minor thermal influence on the useful horizon can be assumed, since the Malm thickness is several 100 meters and thus a sufficiently large heat reservoir is available to rewarm the injected water. An example shows ... the radial cold water spread in the injection horizon at this point in time with a radius of approx. 800 m. "

Heat transport in dense rock

In dense rock, sustainable extraction can only be covered by the heat flow that is supplied by the heat conduction. The heat flow then depends on the coefficient of thermal conductivity. The extraction must then be designed in such a way that the return temperature does not fall below the minimum value determined by the usage concept during the planned operating time.

Emissions

Through geothermal energy, sulfur compounds in the water are washed out and dissolved. As the temperature rises, water can hold less of the climate gas carbon dioxide (CO ₂ ). These naturally occurring gases CO ₂ and H ₂ S are released into the atmosphere by geothermal energy, unless they are technically captured and separated, as is the case with amine scrubbing , which is used in flue gas desulphurisation or direct air capture . However, the cold water can absorb the hot emitted gases again. This opportunity has been used as a cost-effective CCS at the Hellisheiði power plant since 2007 and initially started experimentally in the form of the CarbFix projects, especially since basalt is often available in locations that can be used for geothermal energy.

Risks

Risks of a geothermal project to safety

The near-surface geothermal energy can be set up and operated, provided that the state of the art and sufficiently intensive monitoring and maintenance are maintained, that there are generally no significant risks from such systems. Due to the increased spread of this type of use, however, the risk of technical failure due to overuse of potentials (an unknown system is in the inflow or a system is being built that pre-cools the groundwater flow) or of incorrect planning. The same applies to defects in construction.

The use of deep geothermal energy must be planned and implemented very carefully in order to keep the associated risks within the permissible range for a permit. The deep drilling activities are therefore closely monitored by numerous authorities and require an extensive approval process. The given risk is described as plannable if, for example, the following aspects are taken into account:

Seismic Event Risks

Smaller, barely noticeable earth tremors ( induced seismicity ) are possible in deep geothermal projects in the stimulation phase (high pressure stimulation). Later, if only the steam is withdrawn and not reinjected, land subsidence has occurred due to contraction of the storage rock (for example in New Zealand, Iceland, Italy). These problems have already led to the discontinuation of geothermal projects (for example Geysers-HDR-Project of AltaRock Energy Inc. California 2009 and Kleinhüningen near Basel 2009 ).

The rocks of the Cooper Basin in Australia are considered to be comparatively hot for economic drilling depths and regardless of volcanic activity. When the reservoir was drilled, there was a small earthquake with a magnitude on the Richter scale of 3.7. A deep geothermal project in South Korea is blamed for a subsequent magnitude 5.5 earthquake.

The probability of the occurrence of seismic events and their intensity depends to a large extent on the geological conditions ( e.g. how permeable the water-bearing rock layer is) as well as the type of utilization method (e.g. with what pressure the water is injected into the rock or with what pressure is stimulated ).

In general, a reliable assessment of the risks from deep geothermal energy in Germany, especially in the tectonically active Upper Rhine Graben, is only possible to a limited extent, since there are so far only a few long-term empirical values; The seismicities of Basel and Landau make it clear that careful planning and execution are important for maintaining safety in a geothermal project: Whether stronger damage quakes can be triggered by geothermal energy is currently (as of 2015) controversial, but it was the basis for the discontinuation of the project in Basel. Greater awareness, increased sensitivity and more precise tests lead to delays in use.

Kleinhüningen near Basel (2006)

During the construction of the planned geothermal project Deep Heat Mining Basel in Kleinhüningen in the greater Basel area / Switzerland, there were five slight tremors with decreasing magnitude (from 3.4 to 2.9) from December 2006 to March 2007. This caused slight damage to the building, nobody was injured. A subsequent risk analysis found that the location is unsuitable. The project was canceled.

Landau in the Palatinate (2009)

At the Landau geothermal power plant in Landau in the Palatinate , there were two slight earth tremors in 2009 with a strength of approx. 2.5 on the Richter scale, which, however, should not be causally related to the power plant, as a court opinion in 2014 found.

Landau was a central research location of the BMU projects MAGS and MAGS2 (2010 to 2016) to research induced seismicity. Within the scope of this project, further measuring stations with mainly research tasks were set up. With the commissioning of the Insheim geothermal power plant in 2012, these two power plants will be monitored jointly.

The Landau power plant was shut down in 2014 after new damage occurred. After that there were only several short-term trial operations.

Potzham / Unterhaching near Munich (2009)

On February 2, 2009, two tremors measuring 1.7 and 2.2 on the Richter scale were measured near Potzham near Munich. Potzham is in the immediate vicinity of the Unterhaching geothermal power plant, which was completed in 2008. The measured tremors occurred about one year after this power plant was put into operation. Due to the great depth of the hearth, a direct connection to the Unterhaching geothermal project is questionable. Further microquakes were acc. Geophysical Observatory of the University of Munich in Fürstenfeldbruck observed there after the installation of further seismometers, but they were all below the perceptible limit. Even the biggest events in Potzham were below the perceptible limit according to the Richter scale . It is therefore very likely that they were not felt, but only recorded by devices.

Sittertobel near St. Gallen (2013)

At the St. Gallen geothermal project in July 2013, after several earth tremors at a depth of 4 km up to a magnitude of 3.6, the drilling work was interrupted for several weeks in order to stabilize the borehole. The project later proved to be uneconomical due to the fact that the measured production rate was too low and was discontinued.

Poing near Munich (2016, 2017)

On December 7, 2016 at 6:28 am there was a clearly noticeable earthquake in Poing, Bavaria. The magnitude was 2.1 and the MSK intensity was given as 3.5. On December 20, 2016 at around 4:30 a.m., another earthquake with a magnitude of 2.1 occurred in Poing . From the point of view of some researchers, the geothermal system in Poing may be the cause. Seismic measurements even recorded six earthquakes near Poing in the two months of November to mid-December 2016, four of which, however, were below the perceptible limit. Since the 1990s, earthquakes with a magnitude of 2 or more can be reliably registered and assigned across Germany. Until the events caused by geothermal energy, only a few, barely noticeable quakes were registered in the greater Munich area. Another seismological station has been in operation in Poing in the field of geothermal energy since December 14, 2016. It is used to record the vibration immissions (vibration speeds), because only these can be used to assess a possible damage effect. The reference value according to DIN 4150-3 is 5mm / s. At vibration speeds below this value, even minor (cosmetic) damage to buildings is excluded.

On September 9, 2017, around 6:20 p.m., another earthquake was felt in Poing by many people. According to the German Research Center for Geosciences in Potsdam, the earthquake had a magnitude of 2.4 according to Richter and was triggered at a depth of two kilometers. The Bavarian Seismological Service gives the magnitude as 2.1 according to Richter, and the depth as 3 km. The measured vibration speed was 1.6 mm / s, which rules out damage to buildings. The depth at which geothermal energy is operated in Poing is also 3 km. Around 100 liters per second are taken from the production well at the western exit of the town and, after use and cooling, are returned to the re-injection well at the Pliening municipality border.

Although an earthquake with magnitudes 2–3 is generally only felt very weakly, the people in Poing describe a loud bang or thunder, combined with a tremor that feels as if the entire ground is being lifted as if by a wave. Others described feeling as if something had exploded in the neighborhood. The reason for the bang and the clear feeling of the quake is likely to be the comparatively shallow depth of the quake (only approx. 2-3 km). In principle, seismic events that are associated with a bang are perceived as more frightening than equally strong events without a bang. The bang, on the other hand, has no influence on possible building damage. Two days after the earthquake, Bayernwerk AG temporarily switched off the geothermal system for a few weeks. This happened at the urging of the mayor of Poingen and without admission of guilt by the operator. They want to wait for the results of an expert opinion from the Leibniz Institute for Applied Geophysics (LIAG) commissioned last year before deciding on how to proceed. The Poing earthquake resulted in a referendum in nearby Puchheim in 2018, with a clear majority rejecting the construction of a geothermal system. According to an expert opinion, the earthquakes felt in Poing cannot be held responsible for the damage to the building.

Damage to buildings and infrastructure

Since with near-surface geothermal energy, if the thermal energy is taken from the subsoil by closed geothermal probes, no water is withdrawn from the subsoil (as with a well) and no water is introduced either, if properly carried out, subsidence or uplift of the earth's surface is not to be expected. thus also not with building damage. If such problems did occur occasionally, this is entirely due to improper execution of the flat holes. Here, the shallow geothermal wells have the same risks as shallow wells for other purposes such as subsoil exploration, geotechnics or the foundation of structures.

In 2012 there were almost 300,000 installations of near-surface use of geothermal energy in Germany. Around 40,000 new ones are added every year. Problems have arisen in some cases, but most of all they have indicated a need for improved quality control and quality assurance.

In this context, the massive damage caused by Staufen is outstanding. This and other problem cases are listed below; As a result, the city of Freiburg tightened its requirements for the use of near-surface geothermal energy; they are now subject to approval. In 2008 there were problems with boreholes there in two cases: in one case a sewer was damaged, in another case dirty water gushed out of a dried up spring.

Boeblingen

In Böblingen, there have been increasing cracks in 80 houses since 2009. A connection with the geothermal probe drillings has not yet been proven, but there is a suspicion against older probe drillings through anhydrite sources in the gypsum keuper .

Kamen water cure

In Kamen , after geothermal drilling for the development of near-surface geothermal energy, the houses settled for several days in July 2009. “The reason why 48 cubic meters of soil suddenly disappeared into a hole in Kamen-Wasserkurl has been clarified: geothermal boreholes enlarged existing cracks in the rock. The question of guilt, however, can only be resolved in a lengthy legal process. "

Leonberg-Eltingen

In 2011, test drilling at a depth of 80 meters in the Eltingen district of Leonberg resulted in cracks in around 25 houses. Here, too, draining groundwater led to subsidence. In 2012 the wells were sealed with cement.

Rottenburg-Wurmlingen

In 2002, drilling was carried out in Kapellenweg in the Rottenburg district of Wurmlingen . In 2011 the path had to be closed to through traffic as there were large holes in it. Several buildings were also damaged. Here, too, the cause lies in the gypsum keuper layer, which is slowly washed out by groundwater or rainwater and thus causes the soil to sink.

Rudersberg-Zumhof

In Zumhof, a village in the municipality of Rudersberg in the Rems-Murr district, boreholes for 20 geothermal probes were sunk in 2007 and 2009. The drill pipe broke off when an additional hole was drilled that was not sealed with cement. In October 2012, the rate of uplift there was 7 millimeters per month due to the swelling of plaster of paris. The damaged holes have been overdrilled for rehabilitation since March 2013 and should then be sealed with clay after the drill rods have been recovered. In addition, groundwater is to be pumped out. The drilling company signed a contract with the responsible district office so that their insurance company can pay for the repair. The injured parties must, however, sue the company directly.

Schorndorf

In Schorndorf in the Rems-Murr district, after geothermal drilling at a depth of 115 meters, the groundwater level sank in 2008 because the drilling caused it to drain into deeper rock layers. The resulting lack of volume led to a subsidence of the earth's surface, which damaged the Kepler school and a dozen private houses.

Staufen im Breisgau

→ Main article : Geothermal drilling in Staufen im Breisgau

In Staufen occurred in 2008 after the drilling of multiple boreholes (each about 140 m depth), for heating, inter alia, the town hall, considerable small-scale elevations of up to 20 cm on the built-up urban areas, leading to large strains and sprains or misalignment on buildings. Over 200 houses were seriously damaged. The cause is a reaction of water with anhydrite (anhydrous, dehydrated plaster of paris ). By converting anhydrite to gypsum, the rock absorbs crystal water, which increases its volume. If this happens over a large area, the expansion is possibly transferred to the surface of the day and leads to point elevations there, which deforms the surface of the day. This creates cracks in the affected houses. The problem of anhydrite swelling when it is converted to gypsum is known from tunnel construction and civil engineering and depends on the regional geological conditions (for example in the so-called Gipskeuper in southwest Germany).

Damage is also caused by insufficient geological research (cost savings) and excessive drilling inclination due to "inexpensive drilling" (cost savings). Here savings were made in the wrong place.

The conversion of anhydrite to gypsum is also a natural process whenever an anhydrite-containing rock comes into contact with surface water, rainwater or groundwater within the weathering zone ( hydration weathering ). From a certain depth in the earth's crust, the pressure and temperature conditions are so high that crystal transformation no longer occurs despite contact with water.

The first house was demolished in mid-2013. 270 houses were damaged. The damage is valued at € 50 million. Up to mid-2013, € 7.5 million was used to compensate for the damage, in which the state of Baden-Württemberg and the municipal financial equalization scheme also participated.

General Risks

When pumping thermal fluids ( water / gas ), the constituents of the pumped reservoir water may pose an environmental hazard if the fluid is not cleaned or checked. In Germany, however, the re-injection of the thermal fluids takes place in all geothermal systems, so this is only a theoretical risk.

In the area of ​​near-surface geothermal energy, there is the risk of using a deeper aquifer to penetrate the separating aquifer in such a way that a window is created connecting the aquifer, with the possible consequence of undesired pressure equalizations and mixtures. If the geothermal probe is properly designed, this is reliably prevented. In order to counter this risk, detailed guidelines for quality assurance were set up after the respective damage cases.

Another potential risk with a geothermal well is drilling into artesians . Improper Bohrausführung it can lead to spontaneous loss of groundwater at the drilling location and come to a small-scale flooding.

Even tense (pressurized) gases can unexpectedly be encountered by a deep borehole and enter the drilling fluid. Natural gas, carbon dioxide or nitrogen are conceivable. Such gas inlets are usually not economically viable. In terms of drilling technology, gas ingress must be countered by means of appropriate measures as prescribed for deep drilling. The St. Gallen case has confirmed the effectiveness of these measures.

Rules of technology to minimize risks

In order to master the problem of induced seismicity, the GtV-Bundesverband Geothermie [Geothermal Energy Association] has developed a position paper with the help of an international research group, the main part of which proposes extensive instructions for the management of seismicity in geothermal energy projects.

In connection with building damage in the city of Staufen , a discussion about the risks of near-surface geothermal energy has broken out. Investigations into whether the swelling of anhydrite could be the cause have now been commissioned. As a consequence, the State Office for Geology, Raw Materials and Mining in Freiburg recommended that geothermal boreholes should be avoided in the case of gypsum or anhydrite deposits in the subsurface. Since very small amounts of gypsum / anhydrite can occur in around two thirds of the country's surface, the exact distribution of which is largely unknown, this approach has been criticized by the geothermal industry as excessive.

Baden-Württemberg

After at least have occurred in temporal relation to geothermal utilization soundings Erdabsenkungen in Leonberg and Renningen (both in Baden-Württemberg Böblingen ), the country's environment ministry reduced the maximum drilling depth for shallow geothermal energy: the holes may only to the highest ground water-bearing stratum be drilled .

In March 2015, the State Office for Geology, Raw Materials and Mining made the information system near-surface geothermal energy for Baden-Württemberg (ISONG) available online. It is intended to provide a better risk assessment and hazard minimization in connection with the exploration and use of geothermal energy, as well as “initial information for planning of geothermal probes up to max. 400 m depth ”.

See also : Elevation cracks in Staufen im Breisgau

Instructions on how a safe geothermal well can be made can be found in the guidelines for the use of geothermal energy with geothermal probes from the Ministry of the Environment in Baden-Württemberg.

Risks to the profitability of a geothermal project

Political Risks

Political risks basically consist in the fact that the politically prescribed framework conditions are changed during the project term. The greatest political risk at present (2017) is the new law on the security of sites for radioactive waste management facilities (StandAG). In a first phase, the duration of which is indefinite, this law is based on a 'white map', that is, all locations are reserved for a nuclear repository and may not be used for any other purpose, including geothermal means. This is a de facto ban on geothermal energy with drilling depths greater than 200 m. Permits can only be obtained in a lengthy process with authorities that are not yet able to work.

Economic risks of a near-surface project

In the case of near-surface geothermal energy, the greatest risk is overexploitation of the geothermal potential. If neighboring geothermal systems influence each other, the flow temperature of the system located in the outflow of the groundwater can be reduced so much that the heat pump can only be operated with a very unfavorable coefficient of performance. Then the user basically heats with electricity and not with geothermal energy. The tricky thing about it is that the area in the inflow of the groundwater, in which the construction of another system leads to an additional significant reduction in the temperature of the groundwater for the system concerned, can be very large and it is difficult for the operator to determine the cause to recognize. He will probably only notice this if he relates the outside temperature-adjusted electricity consumption to the amount of heat used in order to be able to observe the coefficient of performance. However, this requires knowledge of the mean effective outside temperature and the amount of heat given off in the house and requires a great deal of measurement effort.

Economic risks of a deep project

In the case of deep geothermal energy, the risk of discovery and the risk of implementation must be taken into account.

If the damage occurs, the risks can lead to the project becoming inefficient. In order to prevent geothermal projects from failing, the public sector offers municipalities guarantees (for example from KfW ) that take effect if, for example, no hot deep water is extracted in sufficient quantities in a well of a certain calculated depth after a deep water discharge can. Some large insurance companies also offer such insurance products.

Finding risk

The exploration risk is the risk when developing a geothermal reservoir that thermal water cannot be extracted in sufficient quantity or quality due to incorrectly calculated forecasts about the required depth of the borehole.

Above a certain depth, the geothermal potential is always tapped, but the drilling costs rise disproportionately with increasing depth and more and more specialized know-how is required. If the available funds and thus the drilling depth are narrowly limited (to a few kilometers, for example), the entire drilling project may have to be terminated a few hundred meters before a usable heat reservoir for a deep water discharge.

The quantity is defined by temperature and delivery rate. The quality describes the composition of the water, which, for example, can have an unfavorable effect on the profitability due to salinity or gas proportions, but is largely controllable from an operational point of view. In order to cushion the exploration risk for the investor, exploration insurance is now offered on the insurance market.

Implementation risk

• During the SuperC project at RWTH Aachen University there were considerable problems with the technical installation underground, but these have since been resolved.
• The project at the Federal Institute for Geosciences and Raw Materials was interrupted because a geologically surprising situation led to the borehole being blocked with precipitated rock salt.

Operational risk

During operation, processes can have an impact on the project that reduce the heat yield to such an extent that unscheduled maintenance work is required (e.g. dissolution of crystal formations through acidification). Since expensive drilling equipment then usually has to be rented and specialists have to be paid, this can lead to the inefficiency of the overall project.

Competing usage

Competing uses for deep geothermal energy can represent projects for hydrocarbon extraction or storage. Above all, the strong expansion of underground gas storage facilities is in direct competition with deep geothermal projects in some regions of Germany (Molasse, North German Plain, Rheintalgraben). Currently under discussion is the competition for use due to the intention of large coal-fired power plant operators and industry to inject liquefied CO ₂ into the subsoil ( CCS technology ). For this purpose, RWE Dea AG has already reserved half of Schleswig-Holstein under mining law. Should an investigation permit be obtained, this area would be excluded from the exploration and use of geothermal energy.

See also

• Marine thermal power plant

literature

Statistical sources

• R. Bertini: World geothermal generation 2001–2005 . World Geothermal Congress, Antalya 2005 (pdf, online).
• Image campaign: Infinite energy.
• J. Lund et al. a .: World wide direct use of geothermal energy 2005 . World Geothermal Congress, Antalya 2005 (pdf, online).
• R. Schellschmidt u. a .: Geothermal energy use in Germany . World Geothermal Congress, Antalya 2005 (pdf, online).
• V. Steffansson: World geothermal assessment . World Geothermal Congress, Antalya 2005 (pdf, online).
• J. Lund: Ground Heat - worldwide utilization of geothermal energy . Renewable Energy World, 2005.

General

• C. Clauser: Geothermal Energy . In: K. Heinloth (Ed.): Landolt-Börnstein, Physico-chemical tables. Group VIII: Advanced Materials and Technologies. Vol. 3. Energy Technologies, Subvol. C. Renewable Energies. Springer, Heidelberg / Berlin 2006, 480-595, ISBN 3-540-42962-X .
• Burkhard Sanner: Geothermal energy for heating and cooling. Potentials, possibilities and techniques of near-surface geothermal energy . Small handbook of geothermal energy. Vol 1. Red. B. Sanner, W., Bußmann. Geothermal Association, Geeste 2001 (3rd revised edition), ISBN 3-932570-21-9 .
• WJ Eugster, L. Laloui (Ed.): Geothermal Response Tests. Publishing house of the Geothermal Association, Geeste 2002, ISBN 3-932570-43-X .
• Geothermal Association, GeoForschungsZentrum Potsdam (ed.): Start into a new energy future . Proceedings 1st specialist congress on geothermal electricity Neustadt-Glewe 12. – 13. November 2003. Geothermal Association, Geeste 2003, ISBN 3-932570-49-9 .
• Ernst Huenges: Energy from the depths: Geothermal power generation. in: Physics in our time. Wiley-VCH, Weinheim 35.2004,6, pp. 282-286, ISSN  0031-9252 .
• F. Rummel, O. Kappelmeyer (Ed.): Geothermal energy, the energy source of the future? Facts - Research - Future / Geothermal Energy, Future Energy Source? Facts Research Future . With the assistance of J. Jesse, R. Jung, Fl. Rummel & R. Schulz. C. F. Müller, Karlsruhe 1993, ISBN 3-7880-7493-0 .
• Stober, Ingrid; Bucher, Kurt: Geothermal. Springer-Verlag, Berlin Heidelberg, 2012, ISBN 978-3-642-24330-1
• Michael Tholen, Simone Walker-Hertkorn: Working aids geothermal basics for near-surface geothermal probe drilling , Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbH, Bonn 2007, ISBN 978-3-89554-167-4 .
• Geosciences magazine , Issues 7 + 8 (1997, special issues on the subject of geothermal energy).
• Magazine special issue bbr near-surface geothermal energy , Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbH, Bonn December 2008.
• M. Augustin, W. Freeden et al .: "Mathematical Methods in Geothermal Energy", Mathematical Semester Reports 59/1, pp. 1–28, Springer Verlag 2012.
• Hausmann / Pohl: CleanTech study series | Volume 6 Geothermie , Bonn 2012, ISBN 978-3-942292-16-0 .
• Bußmann, W .: Geothermal energy - energy from inside the earth. Fraunhofer IRB Verlag, Stuttgart 2012, ISBN 978-3-8167-8321-3 .
• Bauer, Mathias; Freeden, Willi; Jacobi, Hans; New, Thomas: Handbook of Deep Geothermal Energy. Springer-Verlag, Berlin Heidelberg, 2014, ISBN 978-3-642-54511-5
• Rummel, Fritz (1984) Use of geothermal energy. Geosciences in our time; 2, 3; 73-81; doi: 10.2312 / geosciences . 1984.2.73 .

Web links

Renewable energy
Bioenergy Geothermal energy Ocean energy Solar energy Hydropower Wind energy

Commons : Geothermal Energy  - Collection of Images, Videos and Audio Files

Wiktionary: Geothermal energy  - explanations of meanings, word origins, synonyms, translations

• Information service bine.info: Geothermal energy
• buch-der-synergie.de: History of geothermal energy
• Federal Ministry for Economic Affairs and Energy (Germany), erneuerbare-energien.de: Geothermal
  • Deep geothermal energy in Germany - possible uses in Germany (PDF; 3.7 MB)
• Massachusetts Institute of Technology (MIT), geothermal.inel.gov: The Future of Geothermal Energy (English, PDF; 14.7 MB)
• Bavarian State Office for the Environment , Environmental Knowledge , lfu.bayern.de: Geothermal energy (PDF; 1.1 MB)
• Spektrum.de March 26, 2019: We let it shake uncontrollably
• tab-beim-bundestag.de: Status report on the possibilities of geothermal electricity generation in Germany (PDF; 3.3 MB, 2003)
• Tiefegeothermie.de: Information portal deep geothermal energy
• Umweltforschungszentrum Leipzig-Halle , 2015, ufz.de: Interactive online map with all deep geothermal systems and local protest groups in Germany
• Vienna , Technology Guide Geothermal Heat , 2016, wien.gv.at: Geothermal energy ahead! The earth as an energy source (PDF)
• Stefan Hausmann, Daniel Pohl, Patrick Jonas, German CleanTech Institute (DCTI), Bonn 2010, dcti.de: Bioenergy: CleanTech Industry Germany - Drivers in Focus (PDF; 12.5 MB)

Individual evidence

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16. ↑ About the opening of the data center at colocationix.de.
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22. ↑ energyprofi.com , accessed on October 20, 2011.
23. ↑ Masdar Starts Geothermal Drilling (in English) article on RenewableEnergyWorld.com from March 24, 2010.
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28. ↑ Beate Beule: Residual risk - Freiburg tightened requirements for geothermal projects badische-zeitung.de, Lokales, Freiburg, March 16, 2010 (October 17, 2010).
29. ↑ German Research Center for Geosciences : Intelligent Use of Earth's Heat , February 26, 2009.
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33. ^ Geothermal information system for Germany: Directory of geothermal locations .
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35. ↑ Development of the new systems ( Memento of the original from December 4, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . 
36. ↑ Bavarian State Ministry for the Environment, Health and Consumer Protection: Shallow geothermal energy - Overview map Bavaria 1: 200,000, status: May 2006 (PDF 9.6 MB) ( Memento of the original from January 31, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , see surroundings of Ansbach. 
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38. ↑ morgenweb.de  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.  
39. ↑ pfalzwerke.de ( Memento of the original from January 10, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . 
40. ↑ Brühl project objective. (No longer available online.) GeoEnergy GmbH, archived from the original on May 13, 2014 ; accessed on September 21, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
41. ↑ Judges dismiss the lawsuit. In: morgenweb.de. Retrieved May 10, 2020 . 
42. ↑ Final end for geothermal energy in Brühl. In: rnz.de. December 31, 2015, accessed May 10, 2020 . 
43. ^ Project Schaidt . GeoEnergy GmbH. Archived from the original on May 12, 2014. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved May 9, 2014. 
44. ↑ firstgeotherm.de: Data on the Speyer project ( Memento of the original from December 4, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. from FirstGeoTherm 
45. ↑ speyer-aktuell.de: Stadtwerke Speyer lease former geothermal area  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , September 20, 2006.  
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47. ↑ erdwerk.com  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF).  
48. ↑ muenchen.de: SWM geothermal power plant Munich Sauerlach. Retrieved December 3, 2019 . 
49. ↑ Kirchweidach: District heating supplies greenhouses - information portal for deep geothermal energy. In: tiefegeothermie.de. January 7, 2014, accessed June 30, 2015 . 
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51. ↑ geothermie-traunreut.de
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55. ^ Off for geothermal power station near Weilheim . Mercury. January 26, 2018. Retrieved July 10, 2018.
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58. ↑ Rouben Bathke: Groß-Gerau ends deep geothermal project. August 23, 2016, accessed May 10, 2020 . 
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62. ↑ Geothermal project apparently on the brink of collapse . Mercury. December 20, 2018. Accessed December 20, 2018.
63. ↑ The second geothermal borehole also brings the hoped-for result . Alt-Neuöttinger Anzeiger. December 19, 2018. Retrieved December 20, 2018.
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66. ↑ Earthquake: Earthquake , accessed on January 25, 2020.
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68. ↑ Geothermal project of the city of St. Gallen . In: Geothermal Project .
69. ↑ Research Center for Energy Industry e. V .: Low-temperature network with decentralized heat generation .
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72. ^ Carbon Dioxide Solubility in Water
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74. ↑ Archived copy ( memento of the original from October 18, 2019 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
75. ↑ AltaRock Energy § Status in the English language Wikipedia
76. ↑ Geothermal energy under pressure: HDR project within The Geysers site in the USA is being discontinued. heise-online, December 15, 2009.
77. ↑ Economics of Geothermal Energy geodynamics.com.au (October 25, 2007).
78. ↑ CJ Bromley: Geothermal Energy from Fractured Reservoirs - Dealing with Induced Seismicity ( Memento of the original from June 9, 2012 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 278 kB) iea.org, IEA Open Journal 48 , p. 5, issue 7/2007. 
79. ↑ Spektrum .de: We let it tremble uncontrollably
80. ↑ Karl Urban , Deutschlandfunk , January 26, 2015: Danger of earthquakes hinders expansion. deutschlandfunk.de
81. ↑ The Landau quake . In: Der Spiegel . No. 39 , 2009 ( online ).
82. ↑ daldrup.eu
83. ^ Earthquake Service Bavaria: Earthquake in Bavaria since 1390 .
84. ↑ Swiss Seismological Service, current report on July 20, 2013 ( memento of the original from October 25, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . 
85. ↑ Yannick Wiget: Geothermal project temporarily stopped. In: nzz.ch. May 23, 2013, accessed May 10, 2020 . 
86. ↑ Sarah Nowotny: Geothermal energy is threatened. In: nzz.ch. July 20, 2013, accessed May 10, 2020 . 
87. ↑ Earthquake in Bavaria since 1390. LMU Munich, accessed on September 10, 2017 . 
88. ↑ ^{a b} Barbara Mooser: Why the earth trembles in Poing. Süddeutsche Zeitung , December 29, 2016, accessed on December 29, 2016 . 
89. ↑ Interview on the seismic events in Poing. Retrieved September 10, 2017 . 
90. ↑ Another earthquake near Poing. Retrieved September 10, 2017 . 
91. ↑ ^{a b} Barbara Mooser: In Poing the earth shook again. www.sueddeutsche.de, September 10, 2017, accessed on September 10, 2017 . 
92. ↑ Current quakes. Retrieved September 12, 2017 . 
93. ↑ Many years of experience with successful references - Geothermal heating plant Poing. (PDF) Bayernwerk Natur, accessed on September 12, 2017 . 
94. ↑ Geothermal & district heating - energy suppliers in Poing: district heating network. Municipality of Poing, accessed on September 12, 2017 . 
95. ↑ Geothermal energy is switched off in Poing after an earthquake. Retrieved September 12, 2017 . 
96. ↑ Paul Winterer: Poing is waiting for the earthquake report. Welt, September 22, 2017, accessed September 27, 2017 . 
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98. ↑ Barbara Mooser: Reviewers do not see earthquakes as the cause of cracks. Süddeutsche Zeitung, July 8, 2018, accessed on August 6, 2018 . 
99. ↑ Beate Beule: Residual risk - Freiburg tightened requirements for geothermal projects . In: Badische Zeitung , Lokales, Freiburg, March 16, 2010 (October 17, 2010)
100. ↑ badische-zeitung.de, Nachrichten, Südwest, February 26, 2010, Bastian Henning: A dream has burst - Basel, Staufen and Schorndorf in Swabia have shaken trust in geothermal energy (October 17, 2010).
101. ↑ Badische Zeitung , October 25, 2013, Wenke Böhm / dpa: badische-zeitung.de: After geothermal drilling: The earth rises in Böblingen (October 25, 2013).
102. ↑ Information page on the subject of "EARTH RISES in Böblingen" : erde-oben-sich.de (October 25, 2013).
103. ↑ K.-P. Wolter: The cause of the Kamen landslide found. In: derwesten.de. September 24, 2009, accessed June 30, 2015 . 
104. ↑ K.-P. Wolter: Gross negligence in the Wasserkurl landslide. In: derwesten.de. December 18, 2009, accessed June 30, 2015 . 
105. ↑ Marius Venturini: Leonberg: District Office gives the green light for injured parties , stuttgarter-zeitung.de, September 21, 2012, accessed on April 1, 2013.
106. ↑ The ground is breaking away in Wurmlingen , tuebinger-wochenblatt.de, August 30, 2012, accessed on April 1, 2013.
107. ↑ Expert opinion: geothermal boreholes did not cause subsidence ( memento of the original from September 20, 2012 in the Internet Archive ) Info: The  archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , tagblatt.de, August 16, 2012, accessed April 1, 2013.
108. ↑ Landratsamt Rems-Murr-Kreis: Site surveys in Rudersberg are still ongoing ( memento of the original from April 15, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Press release, October 26, 2012, accessed April 1, 2013.  
109. ↑ ^{a b} Oliver Hillinger: Rudersberg: Precise repairs in plaster , stuttgarter-zeitung.de, March 12, 2013, accessed on April 1, 2013.
110. ↑ Landratsamt Rems-Murr-Kreis: Problem solving for site surveys in Zumhof now within reach ( Memento of the original from April 16, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Press release, February 19, 2013, accessed April 1, 2013.  
111. ↑ Armin Kübler: Geothermal energy still harbors risks , schwaebische.de, February 10, 2011, accessed on April 1, 2013.
112. ↑ Jens Lubbadeh: After geothermal drilling: A city tears up. In: Spiegel Online . November 15, 2008, accessed May 10, 2020 . 
113. ↑ Staufen geothermal energy brings down the first house. In: schwaebische.de. August 4, 2013, accessed May 10, 2020 . 
114. ↑ ( For example, recently Arteser at the Hessian Ministry of Finance, Wiesbaden ( Memento of the original dated November 8, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this note. , which was closed after some time with cement of sufficient density ). 
115. ↑ Position paper on seismicity ( memento of the original dated December 23, 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 100 kB) 
116. ↑ State Gazette No. 6 of February 20, 2009, p. 13.
117. ↑ Modernization Magazine 1–2, 2009, p. 9.
118. ↑ Wulf Rüskamp: New specifications for geothermal boreholes. In: badische-zeitung.de. October 5, 2017, accessed May 10, 2020 . 
119. ↑ Backnanger Kreiszeitung , September 8, 2011, bkz-online.de: New limit for geothermal drilling . (September 10, 2011).
120. ^ Bernward Janzing: drilling in a difficult environment - economy - Badische Zeitung. In: badische-zeitung.de. March 7, 2015, accessed May 10, 2020 . 
121. ↑ lgrb-bw.de : Information system for near- surface geothermal energy for Baden-Württemberg ( ISONG )
122. ↑ Guide to the use of geothermal energy with geothermal probes from the Ministry of the Environment in Baden-Württemberg ( Memento from January 8, 2007 in the Internet Archive ) (PDF; 4.8 MB).
123. ↑ Bundesverband Geothermie: Wissenswelt - Lexicon of geothermal energy discovery risk .
124. ↑ Michael Engel: The blocked borehole. In: dradio.de. December 20, 2011, accessed May 10, 2020 . 
125. ^ Association hearing in the BMWi on August 27, 2010 shows considerable resistance to a new approach to the CCS law. .

This article was added to the list of excellent articles on September 23, 2005 in this version .