FAQ



General

Geothermal energy is a sustainable energy source that uses heat that is naturally present in the deep underground (1500-4000m) of the earth. Click here for more information.

In short: Groundwater gets warmer as you go deeper into the earth. With geothermal heat extraction, hot water is pumped up from the subsurface. The pumped water remains in a closed circuit, the heat is transferred via heat exchangers to tap water that is transported via the heat network. When the heat from the geothermal energy has been transferred via a heat exchanger, it is immediately returned to the subsurface. The heated tap water is transported to homes and buildings via a distribution station and the cooled water is returned to the geothermal installation. A home or business is connected to the heat network via a receiving station (also known as a heat unit) in the house or building.

In recent years a lot of knowledge and experience has been gained in the geothermal sector in the Netherlands. There are now more than twenty places in the Netherlands where geothermal energy is extracted. There are also many good experiences abroad. However, it is still important for each project to map out the risks in addition to the opportunities and to take sufficient measures.

Check the page advantages and disadvantages of geothermal energy.

The Heat Act stipulates that geothermal energy may not be more expensive than heating with natural gas. The costs of geothermal energy are stable and predictable; the largest cost item is the preparation and installation of the system. Those costs are one-time. If SDE++ subsidies are taken into account, the costs of heating with geothermal energy are equal to or lower than those of heating with natural gas.

A geothermal heat source has the advantage that the energy supply is independent of external factors such as weather conditions (wind, sun, etc.). As a result, the reliability and stability of a geothermal heat source is high. There will be times when maintenance is being carried out on the geothermal energy project, which means that no heat can be supplied. The heat supply will then continue as usual with conventional heat.

Geothermal energy is considered one of the most sustainable forms of heat production. Geothermal energy is a sustainable source of energy in several ways. Firstly, the supply in the Earth's crust is virtually inexhaustible. Due to natural processes in the core of the earth, the water is reusable (because it is heated up again and again). However, the temperature of the hot soil layers will decrease locally over a period of several decades due to the production of geothermal energy, a decrease that will recover when the doublet is taken out of production. Secondly, hardly any CO2 is released during the production of geothermal energy. During the extraction of geothermal water, gas comes up with it (by-catch) and the pumps used cause some CO2 emissions. In order to be able to make geothermal energy completely CO2 neutral, TNO has investigated how harmful emissions can be minimized through the exploitation of geothermal energy and the distribution in a heat network.

Download the fact sheet 'Sustainability of geothermal energy' here (only in Dutch).

Compared to a natural gas central heating boiler, the CO2 emissions of a geothermal source are about 90% lower. This makes geothermal energy one of the most sustainable heat sources. The CO2 that is indirectly released is created by producing the materials for the well, during the drilling of the well and when pumping up the water. These emissions are compensated or recovered in a few months. If a geothermal company uses green electricity for production, the emissions are even lower, and the CO2 emissions are also compensated more quickly. In 2018, the total of all sources is estimated to result in a CO2 saving of 190,000 tons per year and a natural gas saving of 102 million m3 per year.

It was not. It is one of the most sustainable energy sources. Moreover, the water is returned to the same soil layers so that nothing disappears from the soil. However, the temperature in the deep subsurface will decrease locally by several degrees over a period of several decades. If a geothermal project stops, this temperature decrease will recover.

  • Soil subsidence: in geothermal heat extraction, water is pumped up and returned to the same underground layer. So hardly anything goes on or off in the underground. Partly because of this, the risk of subsidence in the soil is virtually excluded.
  • Vibrations: during the seismic survey, vibrations are generated that can be felt slightly. According to current scientific insights, the effect of the vibrations caused by geothermal heat extraction is negligible. These vibrations are disproportionate to vibrations that have occurred in recent years as a result of gas extraction.
  • Earthquakes: the danger of earthquakes due to geothermal heat extraction is minimal. For example, unlike the gas fields in the Netherlands, no volume is extracted from the subsurface. The water that is pumped out of the reservoir is immediately injected back into the other side. The volume difference is nil in this way. Because small pressure differences arise, this can have an effect on earth layers. That is why there is a legal obligation that geothermal operators may not inject or produce near an underground fault zone. Some areas are excluded for geothermal heat extraction as a precaution. These are areas where earthquakes have occurred naturally.
  • Cooling of the subsurface: over the years, the temperature in the subterranean reservoir may cool down by a few degrees, but most likely this will not affect the subsurface environment.
  • Leaks: with the transport of water from the subsoil, naturally present chemical substances also come to the surface, passing other layers of the earth. That is why extracting geothermal energy in groundwater extraction areas is not permitted. It is therefore important that the wells are as robust (strong and safe) as possible. The design of the wells has greatly improved in recent years, because the sector is continuously working on improving the well design. The new wells have, among other things, double-walled pipes with an epoxy protective layer and an advanced monitoring system.
  • Radioactive sand: along with the water, some sand is also carried upwards. This sand is naturally very slightly radioactive. The sand is captured with filters and processed by a specialized company.
  • Gases: a small amount of gases can also come up with the water from the subsoil. At locations where this is the case, the gas is captured, used to generate heat or, in extreme cases, and flared sporadically.

We already know what the subsurface looks like for large parts of the Netherlands. Thanks to research for oil and gas extraction, much has been known about the composition of the soil since the 1950s. This data is in the data file ThermoGIS. There are no data yet for a number of areas, while these offer opportunities for geothermal energy. Examples of this are Haarlem and Amsterdam. In those areas, seismic surveys can provide answers.

To use geothermal energy, there must be a heat network nearby. This is a pipeline network that transports the hot water from the extraction location to the customers and returns the cooled water to the extraction location. A home or business is connected to the heat network via a receiving station, a box with a heat exchanger in the building or home.

A heat network is comparable to central heating at the level of a district, business park or even an entire city. Instead of heating water yourself with a central heating boiler, hot water comes from the heat pipe via the connection point in the building.

Geothermal energy is supplied via a heat network, which means that the buildings are connected to a heat network. Sometimes adjustments to the heat emission equipment (pipes, radiators) are necessary. It may be necessary to insulate the building to make it suitable for a heat network with geothermal heat with a temperature between 55 and 75 degrees).

Because geothermal energy is extracted underground, geothermal energy is associated with natural gas extraction and therefore with the risk of earthquakes such as in Groningen. Fortunately, the chance of vibrations due to geothermal heat extraction is very small. Extracting gas from the underground gas fields creates a 'hole' that can cause subsidence. With geothermal energy, hardly anything is extracted from the subsurface. The water that is pumped out of the reservoir is immediately injected back into the other side. The volume difference is therefore minimal.

With geothermal heat extraction, small pressure differences can arise due to the gradual cooling of the subsoil. This can potentially affect nearby fractures. That is why strict rules apply to installing and extracting with geothermal energy installations. 

For projects that extract heat from a depth of 500 meters or more, the Mining Act applies and a permit is required. There is a chance that oil and/or gas will be encountered in a geothermal project and therefore the same precautions apply as for projects in the oil and gas industry. State Supervision of Mines (SodM) is the supervisor for all mining activities, including geothermal energy. They are located in The Hague. More information can be found at sodm.nl 

State Supervision of Mines (SodM) is mainly concerned with the following subjects when monitoring geothermal projects:

  1. Assessing work plans, safety plans and the care system associated with a geothermal source.
  2. Earthquake Prevention
  3. Insight into the condition/integrity of wells
  4. Safe collection and processing of water released during testing of the wells.
  5. Ensuring that exploration and production of geothermal energy is carried out as safely as possible SodM therefore provides advice on permit applications under the Mining Act and supervises drilling designs, programs and project approach.

Various permits are required for a geothermal system. For most permits, the Ministry of Economic Affairs and Climate Policy is the competent authority and the State Supervision of Mines is the supervisory authority. Municipalities and provinces have an advisory role towards the Ministry with regard to several permits required. A more detailed explanation can be found here.

Two permits arise from the mining law. The first is an exploration license. This permit entitles the initiator to investigate the subsurface within a defined area for the presence of recoverable geothermal heat by means of test drilling. If the investigation is successful, a production license is required. This gives the (exclusive!) right to extract geothermal energy. In addition, an environmental permit is required in which (the prevention of) effects on the environment are described. In addition, specific permits are required for specific activities (think of possible heavy transport, laying cables and pipes, etc.).

Geothermal energy is considered to be medium temperature heat. Alternatives are residual heat from industry or waste incineration. This is usually high temperature heat. In addition, electrical energy or heat from biomass or energy from wind and sun. Low-temperature heat can be generated via ground source heat or air heat pumps, and from surface water (aquathermal heating), sewerage (riothermal heating) or drinking water pipes.

Geothermal energy is a (mainly) sustainable energy source and can therefore contribute to the energy transition, the transition to sustainable energy sources. Municipalities play a leading role in directing the energy transition. See also How does geothermal energy fit into the regional energy strategy?

After several decades of use, a well may perform less well and/or the technical condition (corrosion or, conversely, deposits) may make it necessary to take it out of use. The aim is 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 top part of the wells and all above-ground installations. However, it is also conceivable that with a new well heat recovery can continue. That depends on the geology at that location and the (technical) developments.

Several factors determine the (maximum) size of a resource. Usually, the capacity of a geothermal reservoir, of which the geothermal source is a part, is considered. First of all, the composition and temperature of the reservoir/formation water and the size of the reservoir are important. These determine the amount of energy that is stored. In addition, the following influences are: the porosity (the amount of open spaces in a rock) and permeability (how well the open spaces are connected to each other) of the rock layer.

The geothermal heat recovery installation is located on a fenced site. This includes a building for the installations such as pumps and filters, areas for storage and an office. Under the environmental law, the geothermal heat developer is obliged to ensure that the site and buildings are properly integrated into the landscape. On the site where a geothermal heating system is located are:

  • The doublet consisting of a production and injection well;
  • Heat exchangers and connection to the heat network;
  • Pumps, filters, degassing installation and a buffer;
  • Building: rooms for pumps, filters, heat exchangers, storage of materials and an office.





Construction activities

The implementation of the geothermal energy project consists of a number of phases. In the first phase, the ground is prepared for construction. Then the drilling phase starts and two geothermal wells are drilled. This is followed by the realization of the geothermal power station and the building, and finally the construction of the new heat network.

Geothermie Delft is committed to preventing and limiting nuisance in the areas of accessibility, liveability and safety. By accessibility we mean: traffic safety, traffic nuisance, accessibility. Liveability concerns, for example, noise, light and odor nuisance. And safety is about the circumstances for people and the environment. All activities meet the requirements of the environmental permit in aspects of noise, safety and traffic. For example, a transport plan, noise and vibration measurements, noise barriers and traffic controllers on the construction site are provided. The project also provides sufficient information and a telephone number that can be reached 24/7. We will also continue to talk to residents and companies about their interests, questions and concerns.

For a timeline of the planning, see Construction & Realisation.

We plan to start drilling mid-November until approximately the end of February. For a timeline of the planning, see Construction & Realisation.

Two wells are required to extract and circulate the geothermal heat. The drilling phase of the project will last three months. During this period, drilling will take place 24 hours a day, 7 days a week. The drilling rig required for this is removed again after the drilling phase. The geothermal source will then be located underground.

The drilling process is accompanied by extra (heavy) traffic for the supply and removal of materials. There is also more noise than usual, such as steel bumping into steel, the sound of the electric motor in the derrick and the sound of trucks. Due to measures, such as the installation of noise barriers, the noise level will remain within the legal standards set for this work. The site is also lit day and night and this also falls within the legal standards that apply to this type of work. When the wells are tested, hot water is collected and transported to a temporary storage, through which water vapor can be visible.

Yes. To prevent possible noise nuisance, lecture and exam periods are taken into account and heavy work is carried out outside these periods.

That is not expected. The forces exerted by a geothermal well on the deep subsurface are too small to lead to noticeable vibrations.

In phase 1: 'construction of drilling location', the traffic situation will remain unchanged. We do, however, take heavy freight traffic on the main roads into account. Traffic therefore travels back and forth from Kruithuisweg, via Huismanweg, Heertjeslaan and Rotterdamseweg. From phase 2: 'construction laydown area', traffic will drive up and down the construction site at Leeghwaterstraat via Cornelis Drebbelweg. The parking lot behind Process & Energy is then used for the storage of materials. Traffic controllers will therefore be placed on Rotterdamseweg and Leeghwaterstraat. Read more about the different phases on Construction & Realisation.

If all goes well, it is expected that sustainable geothermal heat can be supplied to the buildings on the TU Delft campus in early 2024. Later that year, the residential areas of Voorhof and Buitenhof can be connected.

When the installation is in normal operation, the environment hardly notices this. Major maintenance is carried out annually and regular maintenance work is carried out monthly. The installation largely works underground and part of the installations are located in the existing combined heat and power plant.





Location-specific

The project location on the TU Delft campus site is located between Rotterdamseweg and Leeghwaterstraat. In the map below, the location is shown as an orange rectangle.

The heat will initially be used to heat the buildings on the TU Delft campus. The plan is that the Voorhof and Buitenhof districts will also be connected at a later date.

Yes, residential and commercial premises in the Voorhof and Buitenhof districts can also be connected in the future. In collaboration with Open Warmtenet Delft, we are looking at how and where heat can be supplied in these neighbourhoods.

Yes, we keep the surrounding area informed in various ways. We involve local residents and stakeholders through information meetings and individual discussions. Via the website we inform them about the developments in the field of permits, construction and realisation, and research and innovation.

We assume a service life of at least 30 years. However, we expect that the technology will continue to develop quickly so that we can extend the service life even further.





Safety

As Geothermie Delft, we keep the chance of unwanted events small. Nothing is completely without risk, which is why we pay a lot of attention to preventing risks. There are also plans and protocols that come into effect if an incident does occur. State Supervision of Mines is the government agency that monitors and enforces strict compliance with rules by geothermal energy companies.

Fracking is a technique to increase the permeability of rock so that natural gas or oil can be extracted more easily. At a depth of 2 to 4 km, liquid is pumped into the rock under high pressure via the borehole, causing small cracks to form. Fracking has never been used for geothermal sources at a depth of two to three kilometers in the Netherlands. The rocks themselves are permeable enough to provide a high production.

The probability of a minor earthquake has been mapped as part of the seismic hazard and risk analysis. Seismicity is the vibration or jerking movement of the Earth's crust when energy is suddenly released. The analysis shows that the potential for seismicity in this area is low. A risk ranking of the geothermal project was made based on the fractures present, the geothermal energy system designed and the possible presence of natural earthquakes. Negative consequences for nature and the environment due to ground vibrations are therefore not expected. Click here for more information about geothermal energy and seismicity.

Geothermal energy does not permanently remove matter from the subsurface, as is the case with oil and gas extraction. After pumping up, the extracted water is injected again into the same layer of soil. Only the heat remains above ground. As a result, the average pressure in the reservoir remains virtually unchanged, even after years of heat recovery.

In case of emergency call 112.





Water

Disturbing the groundwater is undesirable. Various measures have been taken to minimize this chance and the wells are checked regularly. It is also prohibited to drill through layers of earth from which drinking water production takes place. After all, not every groundwater layer is suitable (or necessary) for drinking water. In the west of the Netherlands (because of salinisation) no drinking water production takes place from groundwater. 

With the 'Industrial Standard for a Sustainable Well Design', the sector guarantees that geothermal energy is extracted safely and responsibly. At the beginning of 2021, the standard was drawn up by EBN and Geothermie Nederland. As of 2021, all new well designs for geothermal wells must comply with this standard. Much has been learned from the first generation of geothermal wells, which has been translated into an industry standard so that we can continue to extract geothermal energy safely and sustainably, without risk to the drinking water supply. Incidentally, there is currently no drilling in (reserved) drinking water areas and there has been no question of any drinking water pollution in the past 10 years.



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