About 25 percent of all the energy we consume is used in the production of heat. This is why enhancing the sustainability of heat production can deliver enormous benefits. In the Netherlands one method that is frequently used to this end is subsurface heat storage. Surplus heat can be stored in the summer, up to a temperature of 25oC, and then be recovered for use in the winter. This TKI research project studies how this temperature limit can be raised as much as possible, so that even more energy can be saved, and what the impact on the surrounding environment would be.
Converting Koppert Cress geothermal energy system
The horticultural company Koppert Cress (Monster) has a conventional geothermal energy system with a capacity to store heat up to 25°C. Since the company in the summer disposes of considerably more heat, greater subsurface heat storage would mean that it would be able to save more energy in the winter, by recovering the heat and using it in its greenhouses. Given the company’s big demand for heat, such an initiative would promote sustainability. To realise this objective, in this project we will be converting the existing Koppert Cress geothermal energy system into a high temperature geothermal energy system.
Clarifying unknown factors in raising temperature limit
It is in practice difficult to raise the temperature limit of 25°C for subsurface heat storage. A number of relevant factors remain unknown. This is why this project focuses on three points that should change this:
- We are sampling and analysing heated groundwater to learn about the effect of higher temperatures on water quality. We are also monitoring the temperature around the sources and in the superior aquifers, in order to get a picture of the heat diffusion.
- We are studying, at various temperature levels, the degree to which calcium dissolved in the water precipitates as calcium carbonate, which can cause clogging. If necessary, we will develop a method to dose CO2 to prevent the precipitation.
- We will study how the buoyancy of the heated groundwater can be limited or offset through a control strategy. Buoyancy is a known phenomenon, in which heated groundwater becomes buoyant because of its lower density. This renders the recovery less efficient.
Fifty percent cut in CO2 emissions
Preliminary research shows that a reduction of at least 50 percent in CO2 emissions can be achieved through the application of high temperature storage (HTO). With regard to the depth distribution, we expect that the water, following infiltration at 40 meters or deeper, will not spread to the superior aquifer situated at a depth of about 25 meters. Preliminary studies also show that that groundwater temperature increases hardly cause any changes in the water’s chemistry and microbiology. The outcomes of this pilot research on the impact of HTO are expected in early 2020. In the event of positive results, the Province of South Holland would favour extending the collaboration between the parties.