About geothermal energy
Explanation: What is geothermal energy?
About geothermal energy
Geothermal energy is a sustainable and renewable source of heat which is present in the subsurface of the earth’s crust. When this heat is transporter to the surface you can use it to heat greenhouses, buildings, homes and use it for (light) industrial processes. A big advantage with using geothermal energy is it barely emits CO2 or fine particles (dust).
Geothermal energy is heat that is generated in the earth’s core. This heat is originally created during the formation of the earth about 4.5 billion years ago.
The interior of the earth consists of a relatively thin crust (about 5-100 km thick), a mantle (about 2,900 km thick) and a core (about 3,470 km thick). Temperatures range from 1,000 to 3,700°C in the mantle and over 6,000°C in the earth’s core. This heat flows from the core to the earth’s surface through various natural processes. The temperature in the subsurface in The Netherlands rises by 3°C per 100 meters. The amount of heat energy in the earth is virtually inexhaustible.
The temperatures rises with increased depth.
At a depth of 2 to 3 km the water temperature is 60-90°C.
In the Netherlands formation water is present in the porous layers in the first few kilometers of the subsurface. This water is heated up by heat coming from the core of the earth up to approx. 100°C.
Deep geothermal energy (conventional geothermal energy) is a proven and applied technology for extracting geothermal energy from approximately 1,000 meters to 3,000 meters. Yeager Energy is mainly involved in deep geothermal energy.
The extraction of geothermal energy is local, sustainable, reliable and affordable.
The word geothermal comes from the combination of the Greek words “gé” = earth/land and “thermós” = warmth/heat. Geothermal energy simply means heat from the earth.
Geothermal energy is energy that is stored under the earth’s surface in the form of heat. The extraction of this (heat) energy has different names, depending on the origin and application.
Heat that is being stored in the shallow subsurface is often called ground-source energy and is often used in shallow ground-source heat exchanger installations.
According to the Dutch mining law, geothermal energy is treated in a similar way as the extraction of other minerals such as oil, gas, salt etc. at depths of more than 500 meters. Yeager Energy is mainly involved in deep geothermal energy.
Yes, geothermal energy was already used by the Greeks and the Romans. Geothermal energy in combination with a district heating network is already being used on a large scale in major European cities such as Reykjavik, Paris, Munich and Milan. In the greenhouse horticulture sector, geothermal energy has been used for heating greenhouses for over 15 years. Currently there are 26 geothermal installations operational in the Netherlands.
Geothermal energy can be used for space heating (homes, companies, greenhouses) and in manufacturing processes in (light) industry. Temperatures can be raised even further with the use of heat pumps. When the temperature of the produced water is high enough, power (electricity) can be generated. This is currently happening in countries like Iceland, southern Germany, Italy, Turkey, Croatia and Hungary as well as Asia, Africa, America and China. Unfortunately, the temperatures in the Netherlands are not high enough for this purpose.
To produce geothermal energy, two wells need to be drilled: a production well and an injection well, together they form a closed system. A pump extracts the water from the porous rock layers through the production well, which is drilled to a depth of around 3 km, to the surface.
In a heat exchanger, the produced hot water transfers its heat to fresh water in the district heating network, which in turn will supply homes, greenhouses and industry with sustainable heat. Usually, the end-customer also has a heat exchanger where the heat is transferred to water in the heating system of this customer. These are all isolated water circuits where heat only is exchanged through heat exchangers.
The salt formation water (water from the subsurface extracted from porous rock layers) will not flow towards the houses, businesses, greenhouses or industry.
After the heat is extracted, the cooled formation water is returned through an injection well(s) into the same porous rock layer where it originated from and where it will heat up again in time. The total amount of water in the porous rock layer remains unchanged.
In the city of Paris, geothermal systems have been used on a large scale since 1969. More than 500.000 residents are being supplied with sustainable heat on a daily basis. The geological/subsurface conditions are similar as those in the Netherlands
Geothermal energy is a proven technique. We are currently in the phase of scaling up this process in the Netherlands
Multiple parameters affect the potential and the output of a geothermal energy source. The capacity of the geothermal reservoir in the deep subsurface from depths of approx. 2.000 to 3.000 meter is the main contributing factor in this.
The characteristics of the formation water and the size of the geothermal reservoir determine the amount of energy stored.
In addition, the porosity (amount of volume in the rock) and the permeability (degree connectivity between the volumes in the rock and how well the water can flow through the rock) are of great influence on the capacity of the geothermal energy system.
In addition, the amount of dissolved (natural) gas in the formation water can also be of influence on the capacity of a geothermal energy system.
Yes, the deep subsurface is suitable for the extraction of geothermal energy in the Netherlands. This energy can be used to heat both homes, offices and greenhouses as well as in in manufacturing processes in the (light) industry.
It is estimated that geothermal energy can contribute to about 30% of the current heat demand in the Netherlands
In the Netherlands, only 4% of households are connected to a district heating network. This is a big contrast to Denmark where approximately 80% of households are connected to a district heating network. To roll out geothermal energy at scale in the built environment am, lot of district heating networks need to be built.
A heat network or district heating network is a collective solution for heating buildings. A heat network is part of a complete energy system. This system can be divided into the heat source, the transportation, distribution and delivery. This network consists of a network of pipelines underground, through which hot water flows. This hot water is used for heating homes, offices and greenhouses. The cooled water is returned to the heat source through separate pipelines where it will be reheated again.
A district heating network connected to a sustainable heat source is estimated to have 50 to 70% less CO2 emission compared to conventional heating systems (gas, oil, etc.). The sustainability of a district heating network mostly depends on the heat source, for example residual heat, biomass or geothermal, as well as the sustainability of the back-up heating systems and the sustainability of the electric power
Only 4-5% of all households in the Netherlands were connected to a district heating network in 2019.
There are different temperature levels for district heating networks. This ranges from high (70°C – 90°C) to middle (50°C – 55°C) to low-temperature (40°C – 45°C) district heating networks. The low temperature networks are usually only suitable for newly developed residential areas (with high insulation).
With a sustainable heat source, such as geothermal energy, to produce this hot water the Netherlands can increasingly stop using natural gas.
Geothermal energy is a sustainable heat source. The CO2 and N2 emissions from a geothermal source are very limited compared to the emissions from using natural gas or other fossil fuels. In addition, very low amounts of fine particles (dust) is emitted during the extraction of geothermal energy.
The average annual production of a geothermal system in the Netherlands is estimated at approx. 180,000 GJ. The reduction in CO2 emissions amounts to approx. 10,000 tons/year (5,500,000 m³ of natural gas equivalent). The use of geothermal energy currently saves more than 181 million m³ of natural gas per year. This is equivalent to the use of natural gas for a city the size of Eindhoven, the fifth largest municipality in the Netherlands with about 240,000 inhabitants.
The pumps, which are used to pump the water out of the production well and into the injection well, require electricity. For the existing geothermal systems in the Netherlands the reduction in CO2 emissions is approximately 88%. When a geothermal company uses green electricity, such as wind or solar, the reduction will be even larger (almost zero).
Geothermal energy is also sustainable since the amount of geothermal energy stored in the earth is virtually inexhaustible.
The extraction of geothermal energy is also a cyclical process and hence this adds to its sustainability – after the energy of the hot formation water, produced by a production well from the deep subsurface, has been extracted inside a heat exchanger, the produced water is cooled down. This cooled water is then injected through another well (injection well) into the same formation where it can heat up again. The two wells form a closed system.
In a number of areas in the Netherlands, natural gas is dissolved in the formation water. This natural gas can remain in solution or be extracted and used. The latter doesn’t sound very sustainable, but it can be.
For example, the gas can be used to generate electricity in a combined heat and power (CHP) installation. In the greenhouse horticulture sector there is a need for a lot of electricity and a certain amount of CO2 gas. The CO2 is used as feedstock for the efficient growth of various vegetables, plants and flowers. In addition to using sustainable geothermal heat for heating the greenhouses they can produce their own electricity and use the CO2 gas sourced from burning the gas in a CHP.
Geothermal energy is currently subsidised by the Dutch government, just like solar and wind energy. The subsidy on geothermal energy is established such that the heat price to the end-customer will not be more than when using natural gas. In Dutch this is called the ‘No More Than Otherwise’ principle (NMDA).
The NMDA is based on the principle that the price for heat in e.g. district heating networks or when using heat pumps that it is on average not more expensive than the use of a natural gas-fired high-efficiency boiler. This principle is laid down in the Heat law.
It is expected that due to economies of scale, cooperation, constant learning, the application of innovative techniques, etc., the costs of geothermal energy will decrease even more, to a point where subsidy is not necessary anymore. This is currently already happening in the offshore wind sector.
The heat price that suppliers of heat are allowed to charge consumers is regulated by the Netherlands Authority for Consumers Market (ACM) and is re-established every year.
Geothermal energy is the most efficient form of sustainable heat energy following the use of natural gas. Unfortunately, geothermal energy cannot be utilised everywhere in the Netherlands.
The capacity of a deep geothermal system is very large, 10 to 30 megawatts (MW). One MW is equivalent to 1,360 horsepower (HP).
Geothermal energy is for example a lot more efficient than ground-source heat systems, aqua thermal energy, all electric solutions, hydrogen, etc.
A single geothermal system can supply 5,000 to 15,000 households with sustainable heat. This depends on the capacity of the geothermal system but also the degree of insulation of homes. This also means that geothermal energy is also very efficient in saving CO2 emissions.
The large capacity of geothermal energy systems means that major steps can be taken in creating a sustainable heat supply in the Netherlands.
With the extensive experience abroad and the experience in the past fifteen years with geothermal energy in the Netherlands, geothermal installations (and its heat supply) have proven to be reliable and safe. A company that supplies sustainable heat is required to guarantee the supply of it.
During short interruptions of the geothermal energy production (e.g. during maintenance periods), a heat buffer and/or underground heat storage will provide continuous production.
When a geothermal installation is not in production for a longer period, backup installations will provide the continuous supply of heat.
In addition, it is expected that in the future geothermal installations will become part of regional networks with other geothermal sources and installations, but also other heat sources such as residual heat, aqua thermal heat, bio-heat and, during the transition period, also gas-fired power plants. In the event of prolonged disruptions, the sources in such a network can take over the heat production.
Over time, the produced water slowly cools down to a point where it can no longer be extracted commercially. It is expected that this takes more than 30 years.
This means that the production well will be closed in for later use to allow the water in the porous rock layers to heat up again. New geothermal wells will need to be drilled to continue the production for another 30 years or more.
Geothermal wells can last a very long time. The oldest wells in Europe have been producing for over 150 years.
The extraction of geothermal energy is a regulated industry. The regulator, the State Supervision of Mines (SodM), is committed to personal safety and the protection of the environment when extracting energy and the use of the subsurface. This is laid down in the Mining law.
The objective in geothermal energy production is to prevent undesirable events from taking place or the chance of this happening minimised as much as practically possible.
The drilling of geothermal wells is designed and executed in the same safe way as gas wells. The Industry Standard for a Sustainable Well Design is being used, which has been drawn up by the trade association ‘Geothermie Nederland’.
Encountering gas in the drilling phase is therefore not a problem. When geothermal wells are closed-in (no production) the surface pressure will be zero. Geothermal wells have all the necessary safety measures and devices (such as safety valves) that can withstand high pressures.
With the production of geothermal energy, the net volume of formation water produced from the subsurface (from the porous rock layers at a depth of 2 to 3 km) is returned to the same formation, and therefore no net extraction takes place. This is different with oil, gas and salt production from the subsurface. After the heat energy has been extracted in a heat exchanger, the produced hot water is cooled and injected again in the same formation (a cyclical process). As a result, the average pressure in the reservoir remains virtually unchanged.
As there is no net volume of water produced from the subsurface and hence pressure differences during production are very small, it is very unlikely that seismic activity or subsidence will occur as a result.
The drilling of geothermal wells can go through shallow layers of groundwater (but never through protected groundwater areas or drinking water-bearing layers – see also next question “Does geothermal energy endanger drinking water areas?”).
When drilling a well, a drilling fluid (a viscous clay fluid, also called drilling mud) is used to cool the drill bit, to bring the drill cuttings to the surface and to maintain hydrostatic pressure on the formations so that the well does not collapse. The drilling mud plasters the walls of the formations so there is no or minimal influx of this mud into the formations.
Subsequently, the borehole is secured using large steel pipes (casing) with cement between the casing and the walls of the borehole.
During the production phase regular integrity checks of the wells are conducted to ensure the safety and integrity.
It is not permitted to drill through drink water-bearing layers in the Netherlands. Provinces exclude mining activities in water extraction areas, groundwater protection areas and drill-free zones. The government will not issue an environmental permit for these activities.
Drilling from outside the boundaries of these protection areas to locations far below the groundwater sources is allowed, provided there are no risks to the quality of the groundwater.
The various activities in the subsurface in the Netherlands see more and more conflicts of interests. Particularly the drinking water and mining sectors, which include the production of geothermal energy, as well as oil, gas and salt production and underground storage.
The government has therefore drafted a document ‘Structuurvisie Ondergrond’ (STRONG) which includes strategic policies concerning the use of the subsurface for the key national interests: drinking water and energy. The objective of this document is to find a balance between protecting and utilizing groundwater for the drinking water supply and providing space for mining activities for the energy supply.
STRONG states that the supply of drinking water and mining activities are both of equal national importance.
In this vision, the central goal is to ensure ‘sustainable, safe and efficient use’ focused on the national interests of ‘drinking water supply’ and ‘mining activities’. This structural vision aims to ensure that:
In the west of the Netherlands there is no direct production of drinking water, but a so-called ‘open infiltration production’ in which water produced from outside the dune areas (outside the province South-Holland), surface water (rivers, IJsselmeer) is transported to the dune area and infiltrated from the surface, filtered through the dune sand and then pumped up again from a depth of some 40 to 70 meters.
There is no direct production of drinking from water-bearing layers at depths of several hundred meters.
The produced ‘formation water’ contains dissolved natural substances and minerals. It has a high salt content. This water does not come into contact with any surface water or the air. The geothermal system of a production well, a heat exchanger and an injection well is a closed system.
Small sand particles and other solids (hundredths of millimeters in size) can be produced. In order to prevent the blocking of the injection well, filters are present in the surface installations.
Effects on the environment
Wells need to be drilled before geothermal energy can be produced. Drilling operations can cause some nuisance to residents. Hence various permits are required, plans need to be presented (such as a traffic plan) and good communication with the municipality and residents need to be established. A close co-operation with the municipality is of great importance.
The preparation of the drill site and the installation of the drilling rig can take several weeks and often takes place during the day. Some nuisances can be caused by work traffic and driving of piles.
Drilling takes place 24 hours a day, 7 days a week. A drilling rig is electrically powered and produces light and noise. Trucks are used for the supply and removal of equipment and materials.
The drilling of the two wells (a production well and an injection well) required for a geothermal system will take several months.
Yeager Energy will keep the nuisance for residents to a minimum during the construction and drilling phases. The noise level will be continuously monitored.
Geothermal heat production does not cause any nuisance to residents. The pumps of the production installation produce some noise, but this is not audible outside the production site. A building for the geothermal installation will be constructed which will fit in the surroundings.
Residents should be aware of limited truck traffic (approximately once every two weeks).
A degassing installation may be present at the geothermal installation to burn gas (dissolved gas) during emergencies. This ‘flaring’ only takes place under unusual circumstances as a safety measure and the testing the flare produces some noise (1 time every 2 weeks).
The geothermal installation is surrounded by fences. Under the environmental law, the geothermal energy company is obliged to ensure that the site and the building are properly integrated into the landscape.
At the site of a geothermal energy system you find: