Geothermal energy (geothermal heat) is mentioned as the sustainable alternative to natural gas. But is that really so? For example, are our groundwater resources well protected in these advancing soil activities? The advantages and disadvantages of geothermal energy and geothermal heat.
What exactly is geothermal?
Geothermal energy is the scientific name for geothermal heat. A distinction is made between two types: shallow geothermal energy (between 0 – 300 meters) and deep geothermal energy (up to 2500 meters in the ground).
What is shallow geothermal?
Niels Hartog, researcher at KWR Watercycle Research: “Shallow geothermal energy consists of systems that store seasonal heat and cold, such as soil heat exchanger systems and heat and cold storage (WKO) systems. In the summer, hot water from the shallow subsurface is stored for heating in the winter, in the winter cold water is stored for cooling in the summer. ”These systems are mainly used in urban areas and in residential areas.
What are ‘open’ and ‘closed’ systems?
Hartog: “A bottom heat exchanger system is a closed system. This is where thermal energy is exchanged over the wall of a pipe in the ground. At a WKO, hot and cold water is pumped and stored in the soil. Because active water is pumped here and out of the sand layers into the soil, this is also referred to as “open” systems.
What is deep geothermal energy?
With deep geothermal energy, a pump with water at a temperature of 80 to 90 degrees is extracted from the soil. It is warmer in the deep subsurface, hence the term geothermal. “That is possible all year round, because the seasons have no influence on the temperature in the deep subsurface. Greenhouse horticulture started with this some ten years ago. Now it is increasingly being looked at how deep geothermal energy can also be used in inhabited areas as an alternative to gas. ”
“Deep geothermal energy is mentioned as an alternative to gas”
Is it an infinite source of energy?
Deep geothermal energy is not by definition an infinite source of energy. The heat is removed from the soil and this is partially supplemented each time. Over time, the system may become less efficient. Regarding CO2 emissions, it is much more sustainable than the use of fossil fuels.
Geothermal heat: benefits
- Sustainable source of energy
- No CO2 emissions
Terrestrial heat: disadvantages
- High construction costs
- Small risk of earthquakes
- Risks of groundwater pollution
What is the influence of geothermal energy on drinking water supplies?
Groundwater supplies that are used for drinking water production are located at depths up to 320 meters in the soil. These stocks are protected by a tens of meters deep clay layer. In geothermal practices, water (which is not used for drinking water production) is displaced or liquids are piped into the soil. For such systems, drilling is required in the soil. As geothermal activities often take place at hundreds of meters, it may be necessary to drill through groundwater supplies. In a 2016 KWR report, Hartog set out a number of risks to groundwater supplies:
Geothermal: three risks for drinking water
Risk 1: The drilling is not going well
Drilling groundwater packages through insufficient sealing of separating layers can cause groundwater contamination. Drilling mud with potentially contaminated substances can also penetrate a water-bearing layer (aquifer) or groundwater packages. And contaminations in the shallower subsurface can end up underneath this layer by penetrating a protective layer.
Risk 2: Groundwater quality deteriorated due to residual heat
The degree of heat emission from the well can lead to changes in groundwater quality. Groundwater may not be warmer than 25 degrees. What quality changes can occur is unknown and probably strongly location-dependent.
Risk 3: Pollution from old oil and gas wells
The proximity of old abandoned oil and gas wells near the injection well of geothermal systems leads to a risk for groundwater. Old wells may have been damaged or insufficiently sealed. This allows formation water from the geothermal reservoir to rise via an old well and end up in the groundwater.
With every form of geothermal there are risks for drinking water sources
Geothermal: not in drinking water areas
With deep geothermal energy but also with the shallow thermal systems there are therefore risks for groundwater supplies that we use as a source for drinking water. The drinking water companies, but also the SSM (State Supervision of Mines) are therefore critical of mining activities such as deep geothermal energy in all drinking water extraction areas and areas with strategic groundwater reserves. Provinces have therefore excluded thermal and geothermal energy in protection areas and bore-free zones around existing extraction sites. Central government has adopted this exclusion of geothermal energy in drinking water areas in the (design) Substrate Structure Vision.
Clear rules and strict requirements required
For shallow geothermal energy, ie the thermal storage systems, clearer rules and stricter requirements for a permit for geothermal heat systems are being worked on. Hartog: “That way you prevent cowboys from coming onto the market and you give good companies the opportunity to build a reliable and safe system elsewhere, in consultation with the province and the local drinking water company.”
‘Safety culture a problem’
But with deep geothermal energy there are not yet clear rules. In addition, drinking water companies are concerned about the safety culture in the geothermal sector. According to a report from the SSM, this is not good and the focus is not so much on safety, but rather on cost savings.
It is not specified how monitoring should be arranged
‘Monitoring not properly arranged’
It is mainly about how you carry out the drilling and well construction, says Hartog. “It’s about where you drill, how you drill and how you seal a hole. The material for the wells and the amount of walls are also important. The system must be as watertight as possible. ”According to the critics, this is precisely the problem. To perform geothermal energy safely, good monitoring is required so that any problems can be detected and action can be taken quickly if things go wrong. However, the rules do not specify how such monitoring should be arranged.
Is ‘safe’ geothermal energy possible?
Absolutely, says Hartog. It is not a matter of one or the other, it is mainly how you do it. It is important to involve drinking water companies in the development. “They possess a wealth of knowledge about the soil. So they know exactly what is needed to properly protect groundwater supplies. ”
In several areas, the Province, drinking water companies and producers of geothermal energy are already working together intensively for good agreements. For example, a ‘green deal’ has been concluded in Noord-Brabant stating, among other things, where underground activities may and may not take place. There is a similar partnership in Gelderland.
‘Working together on a solution’
According to Hartog, there is no other choice than good cooperation between all parties involved. “We want to get rid of gas, generate sustainable energy and at the same time have high-quality and affordable tap water. That is possible, but then we must cooperate constructively and not engage in a mutual struggle. That is counterproductive. In a new research program we are now looking at how water knowledge can be used sector-wide in the circular economy. ”
The gas and energy transition in the Netherlands is currently moving at a rapid pace. For shallow open geothermal systems, substantial growth is predicted: currently there are 3,000 open soil energy systems, by 2023 there must be 8,000. Where exactly they should go is still unknown. Additional groundwater reserves are also needed for the future drinking water supply that must be designated. Provinces and drinking water companies are therefore investigating how both space claims can be realized. Function separation is the starting point.
According to Hartog, the knowledge that has been gained in recent years and the agreements that have been made have created a kind of national blueprint. “You then look at the specific requirements of a geothermal system for each location. The substrate is different everywhere and the clay layers differ in thickness. ”
“Sustainable, but not without risk”
Finally, Hartog emphasizes that we should not close our eyes to possible negative effects on the environment. “I often compare it to the rise of an electric car: a sustainable development, but you can still hit someone with it. In short, that development in a broad sense and in the longer term is positive does not mean that there are no dangers. ”