Shallow(er) geothermal resources successfully utilised for Dutch greenhouse operations
With an increasing blurring of lines between shallow geothermal and what we describe as deep geothermal energy utilisation, this low-temperature not so deep project to utilise geothermal energy for greenhouse operations is incredibly interesting.
Aubergine nursery Greenbrothers in Zevenbergen in the Netherlands is the first company in the Netherlands that uses shallow [shallower] geothermal energy.
Visser & Smit Hanab – a VolkerWessels company – carried out the pioneering project, in which low-temperature geothermal energy (LTA for short) heats Greenbrothers’ greenhouses, as reported by Techniek Nederland. The LTA installation uses geothermal heat with a temperature of 31 degrees C that can be upgraded to 60 degrees C with a heat pump.
LTA is a new type of geothermal energy that combines the advantages of a thermal energy storage system with those of deeper geothermal energy, while it does not have the known disadvantages of these forms of sustainable heat extraction. Due to the extraction of water from relatively shallow layers of earth, the temperature of that water is “only” around 30 ° C, which means that the heat needs to be upgraded.
A study by DLVGE, KEMA and IF Technology into energy from less deep strata in 2014 revealed the potential of LTA. Ronald-Jan Post, energy manager at Greenbrothers, was one of the people involved in this study. “Based on the research, various soil maps could be made, which also revealed the possibilities for Zevenbergen. This put us on the trail of LTA, with Visser & Smit Hanab (V&SH) as the implementing party, for the sustainable heating of our greenhouses. ”
The different geothermal technologies, including geothermal energy
“The choice of LTA was obviously not made overnight,” said Post. “The principle of LTA had never been applied before, and such a pioneering project involves uncertainties and risks. That is why we also looked at alternatives with Greenbrothers, such as residual heat from Moerdijk or building a fermentation installation. But taking all the pros and cons into account, we eventually chose LTA. ”
Mark de Vrieze, project manager at V&SH, indicates that this choice was an obvious choice for the Greenbrothers project. “The goal of Greenbrothers was to heat the greenhouses in a sustainable way. Both CHP and deep geothermal energy were not an option. Because Greenbrothers only needed sustainable heat and had almost no cold demand, a thermal energy installation was not a realistic choice. ”
Deep geothermal energy was also not an option for the sustainable implementation of the heating of the greenhouses. “It is geologically impossible to apply deep geothermal energy in Zevenbergen,” says De Vrieze. “In the search for opportunities for profitable sustainability, you always depend on the environment. For Greenbrothers, this meant that LTA was the best solution for heating the greenhouses sustainably. ”
Special drilling method
V&SH provided the drilling for the “shallow geothermal energy”, as LTA is also called. To do this, the company drilled into the earth layer “Brussels Sand”, which is located in Zevenbergen at about 700 m depth. V&SH developed a special drilling method to extract the geothermal energy from the Brussels Sand in a profitable manner. “The sand layer from which we extract the heat is relatively thin,” explains De Vrieze. “If we opted for vertical filters, the temperature of the water in combination with the amount of water we can pump up would not be in proportion to the costs.”
Shallow geothermal aerial view
That is why V&SH developed a method to drill and place the filters horizontally in the Brussels Sand. This technique is somewhat comparable to directional drilling for pipes and cables under, for example, rivers and roads. De Vrieze: “In doing so, we drill two wells at an angle from each other at an angle downwards. This creates enough space between both wells, without us having to go very deep. Then we drill horizontally and place the filters there. By applying the filters horizontally, we can extract warm water over a much greater distance. With this greater flow and the lower temperature in these less deep layers of the earth, this results in sufficient power.”
According to De Vrieze, the use of LTA has several advantages. “Due to the relatively low temperature and composition of the water we pump up, there is much less corrosion in this project than in deep geothermal energy. As a result, the pipes do not have to consist of extra resistant materials, which means that the costs for materials and maintenance are significantly lower. In addition, you do not have to use inhibitors or chemicals.”
“The less deep bore also ensures that we are not dealing with lightly radioactive substances,” De Vrieze continues. “Furthermore, the amount of gas in the water that we pump up is minimal: about 0.06 cubic meter of dissolved gas per cubic meter of water. That is so little that we keep the entire system closed and no degassing is required. This in turn has a positive effect on the corrosion and any precipitation in the injection well.”
The creation of the LTA installation had many feet, both literally and figuratively. “It was the first time that such a project had been realized,” says Post. “In projects where techniques and methods are applied for the first time, you often have to deal with teething problems. That was also the case with us. ”
One of the setbacks faced by the project was the leak in the reservoir, causing sand to leak into the pipes. Post: “That leakage blocked the pipes with sand. After we found the leak, it was repaired and the pipes were vacuumed so that we could continue. ”
In addition to the leakage, the project group was also faced with a second challenge: the well pump that collects the hot water got stuck and no longer pumped up water. De Vrieze: “The solution is theoretically simple: replace the pump for a new one and continue again. In practice, it is quite an operation to replace such a pump. ”
Post adds: “When replacing the pump, we noticed that this project really differs from projects with above-ground installations.” De Vrieze: “Something like this costs time and money, just like everything that deviates from the theory costs time and money. It is therefore important that you prepare different fallback scenarios for this type of situation. The experiences we have now gained are very valuable for this. ”
Greenbrothers’ objective was to reduce CO2 emissions for heating the greenhouses by 80%. “It seems that we are going to achieve that goal, although it is too early to say this with certainty,” says Post. “The installation has been active since December 2019, so it is still running a little too short to draw final conclusions about the performance. We are currently fine-tuning the system. ”
De Vrieze: “With the shallow geothermal energy, we generate 25,000 MWh of energy every year, and the heat is upgraded via the heat pumps.” The heat pumps to which De Vrieze refers are used in series; a modular heat pump system consisting of three heat pump modules ensures a good upgrade of the geothermal heat while maintaining a good efficiency. The result is impressive: an annual saving of 9,000 tons of CO2.
Post is satisfied with the results of the completed LTA installation. “We are the first parties to have done this. Of course there are areas for improvement for a next project, but that is always when you start working with new techniques. The great thing is that this information is available in a subsequent project with LTA. With this installation we can supply our greenhouses with heat in a sustainable way all year round, so LTA is a great solution for us. I wonder what role LTA can play in other issues in the future. ”
Source: Techniek Nederland