Wat is aardwarmte?

Geothermal energy has a number of advantages.

• it is a sustainable source of energy that hardly emits CO2. For (greenhouse) heating with geothermal energy, the average emission is approximately 1/8 of that of natural gas (electricity is still needed for the pumps, etc., and assuming a COP = 20,500 g CO2/kWh of electricity);

• the costs of geothermal energy are stable and predictable over a longer period of time;

• In contrast to many other forms of renewable energy, geothermal energy is independent of external factors (wind, sunlight, etc.). It's available 24/7;

• Once the wells have been drilled, there is hardly any noise pollution or visual nuisance to the environment.

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Geothermal companies are focused on keeping the risk of adverse events to a minimum. This mainly concerns:

• seismic activity. Human actions in the subsurface can cause (larger and) smaller earthquakes and vibrations. However, the forces that a geothermal bore or source exerts on the subsoil are too small on their own to lead to perceptible vibrations at ground level (approximately 2.5 kilometers “higher”). Because the pressure differences in geothermal energy are very small during operation, it is very unlikely that this will cause earthquakes;

• subsidence. No volume is extracted from the subsoil, as is the case with mineral extraction. As a result, the average pressure in the reservoir remains almost unchanged. Injecting cooled water ensures that there will be some shrinkage in the rock around the injection well. This is in the order of 2 centimetres after 100 years of production and is therefore negligible in the event of the natural subsidence or increase in a century. Noticeable subsidence due to geothermal energy is therefore not to be expected. Sometimes a small amount of gas (or oil) comes along with the water. This is called bycatch. This by-catch is so small in volume that no subsidence will occur as a result;

• groundwater pollution. Wells are drilled and secured with cement in such a way that the chance that water from one layer of the Earth will end up in another layer is nil. Conductors (large steel tubes of 50 to 200 meters in length, which are installed first) ensure that the drilling fluids do not end up in the (shallower) soil. Regular monitoring of the well condition also takes place during heat production, for example by measuring the thickness of the well wall and the pressures;

• (gas) explosions. Geothermal drilling is carried out in the same safe way as gas drilling. So if gas is found, that is no problem. On the surface, geothermal wells are depressurized when stationary. However, geothermal sources have built-in safety devices (such as valves) that can withstand high pressures.

The geothermal companies are supervised by State Mines Supervision and, where appropriate, by the fire department and the municipality.

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The pumped up “formation water” contains all kinds of dissolved natural substances/elements. The water does not come into contact with surface water or the outside air. The management and systems are aimed at pumping these substances back into the injection well. However, small particles of sand and solid particles can come with the flow. The aboveground installations include filters that filter out these particles to prevent the injection well from clogging. (Those particles are still very small: hundredths of a millimeter.) Sometimes these particles have a slight natural radioactivity. These slightly radioactive particles occur on Earth in both the upper and deep subsoil. This is a type of radiation that is easy to shield and cannot be measured on the outside of the installation. The internal procedures when opening the installation take this into account and the environment is not affected.

This component is supervised separately by the ANVS (Authority for Nuclear Safety and Radiation Protection).

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After several decades, use may cause a well to perform less and/or the technical condition (corrosion or, on the contrary, tarnish) decommissioning make it necessary. The aim is then to restore the original situation in the subsoil as much as possible. This is done by partially filling the wells with concrete and removing the upper part of the wells and all aboveground installations. However, it is also conceivable that heat extraction can continue again with a new well. That depends on the geology at that location and (technical) developments.

Geothermal energy is energy in the form of heat stored in the soil. This means that all energy that comes from the soil in the form of heat can be called geothermal energy or geothermal energy. This can be energy from natural sources, such as when using a geothermal source. Heat that is stored in the soil by humans, such as Heat/Cold Storage (WKO), is often called “shallow geothermal energy”, especially abroad. In the Netherlands, we usually talk about 'soil energy'. In the Netherlands, (Deep) geothermal energy - in accordance with the Mining Act and the regulations governing it - formally involves depths of more than 500 meters. For more information about soil energy systems, you can contact, among others, www.bodemenergie.nl.

From 'shallow' to 'deep', there are:

• ground heat pumps (usually individual houses/buildings), maximum around 50 meters deep;
• WKO systems (larger offices and groups of homes), maximum around 250 meters deep;
• MTO (Medium Temperature Storage);
• HTO (High Temperature Storage);
• deep geothermic/Direct Use (collective applications without a heat pump such as residential areas and greenhouses), maximum around 1,500 - 4,000 meters deep;
• ultra-deep geothermal energy (electricity, industry and district heating).

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The production of geothermal energy hardly releases CO2. The pumps, which pump water out of the production well and into the injection well, require electricity. For the sources achieved so far, the average CO2 emissions are approximately 7 kg/GJ, compared to 57 kg/GJ for natural gas, an 88% reduction. If a geothermal company purchases green electricity, for example produced with windmills or solar panels, this is of course even lower (almost zero).

(Principles for this calculation: a COP (Coefficient of Performance) of 20 and an emission of 500 grams of CO2 per kWh)

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The Earth's crust gets warmer everywhere you go deeper. However, the presence of water in a sufficiently permeable reservoir is necessary to also be able to obtain and use this heat above the ground. For example, on http://www.thermogis.nl/basic.html is to get a good idea of which areas and at what depths how much heat can be extracted. These maps go to a depth of up to 3 -4 kilometers and also have uncertainties. These are listed on the website.