When using geothermal energy, hot water or steam is extracted from the subsurface. The energy can be used for the production of heat and electricity. Geothermal sources and uses vary in line with the aquifer temperature (groundwater) from which the water is extracted. When the temperature of the aquifer is between 15 and 200 °C (at a depth of one hundred meters to around 6000 m), geothermal heat can be used to provide heat for individual buildings and district heating networks. The deeper the geothermal well, the hotter the extracted water is. A distinction is made between deep and shallow geothermal energy. Shallow geothermal, depending on the definition, is a depth of 250 to around 1250 meters. Heat and cold storage is done at even lower depths of up to 250 meters. Heat pumps are needed to bring the temperature to a usable level with shallow geothermal energy. Deep geothermal heat can be applied directly. Geothermal sources with a typical temperature of 160 °C or higher can be used in industrial processes and for electricity generating turbines. Each geothermal source is unique in its location, temperature, depth, and type of use.
There is increasing interest in the development of geothermal energy to replace natural gas as a source of heating, steam or clean electricity. In the Netherlands, the planned closure of the large Groningen gas field has intensified the development of alternative ways to heat buildings and greenhouses, such as the use of geothermal heat. According to the Geothermal Energy Master Plan, around 25% of heating demand in the Netherlands can be supplied by geothermal energy in 2050.
Geothermal energy, with 2.4% of the renewable energy used in the Netherlands (and 0.2% of the total energy consumption) in 2018, represented only a small part of the contribution of renewable energy to total energy consumption. The main reasons for this are the geological risks associated with the development of geothermal resources. The reduction of geological risks will attract commercial investments. Thanks to the drilling of new geothermal sources and seismic campaigns to obtain subsurface data, geological and geothermal risks will be limited in many areas in the Netherlands in the coming years. Research also leads to cost savings, which contributes to the ever broader deployment of geothermal energy. Cost savings are achieved, for example, by developing a geothermal portfolio of several wells instead of working project by project. Other cost savings include a reduction of drilling costs and the use of stimulation techniques that can improve production and other production optimization measures. Besides, significant savings can be achieved by applying substantial seasonal storage to use geothermal heat effectively. This for reasons of the much higher heat demand in winter than in summer.
Geothermal energy is generally regarded as environmentally friendly, sustainable and reliable. However, like all other sources of energy supply it also faces sustainability issues. Polluting emissions are generally considered to be minor in comparison to the pollution associated with fossil fuels (e.g. coal, oil, and natural gas). The main emission risks are leakage of reservoir fluids into groundwater (freshwater reserves), co-production of natural gas and induced seismicity. These risks are considered as very low and can be managed. Globally, geothermal power has considerable potential for growth; however, necessary steps need to be taken to see that growth is coupled with sustainability.
While most geothermal heat is used space heating, agriculture (primarily for heating greenhouses) has long been an important end-use sector in some countries. In recent years, the energy intensive greenhouse horticulture sector in the Netherlands has expanded geothermal use thanks to strong policy support. The first project was started in 2008, after which the number increased to 22 in 2018. There are also 50,000 individual (shallow) geothermal heating systems in the Netherlands. Although greenhouses in the Netherlands remain important customers, the focus is increasingly shifting to the built environment and, in the future, to low temperature industrial heat (100 – 200 °C). Elsewhere, new developments in geothermal heat have focused primarily on district heating. Nine new production sites were taken into operation in the European Union in 2017, with 75 MWth of new capacity in France, Italy and the Netherlands. The Netherlands is one of the fastest growing European markets, especially in the heating sector.
Geothermal energy can play an important role in the energy transition in many places in the world, in the Netherlands in particular by replacing the use of natural gas for space heating, heating of greenhouses and in the future heat with lower temperatures in the industry.