The greenhouse horticulture sector in Flanders has been at the forefront when it comes to innovative ways of heating greenhouses for many years. Efficient heat production is essential for the sector. VITO is working together with Thomas More University of Applied Sciences (Campus Geel/KU Leuven) on researching methods of using heat from deep underground in a profitable way. The use of geothermal energy is a renewable energy source that has been overlooked in Belgium for many years.

Research Coordinator Ben Laenen explains: “VITO has already spent several years researching the possibilities of using heat found deep underground to provide heat on the surface. The deeper you drill down, the higher the temperature, and the temperature rises by around 30°C on average for every thousand metres. This is of interest to the greenhouse horticulture industry, but it goes without saying that this heat is also of interest to many people and organisations, such as heating networks for residential districts, swimming pools and other public institutions.”

Geothermal energy in the northern Campine

The ideal substrate for heat extraction is one with gravel layers containing high levels of water that will also flow easily. That exists in the northern Campine and in the Borinage, where limestone can be found in the earth at a depth of between 1000 and at least 4000 metres, which is suitable for heat extraction. The search for hot water from the limestone layers in the Campine was carried out by two market gardeners in Dutch Limburg. The Wijnen brothers heard about a successful geothermal energy project run by a tomato grower in the Dutch town of Bleiswijk, and wondered whether a similar project could also have a chance of succeeding for their own greenhouses in Grubbenvorst in the Netherlands. Geologists in the country didn’t think so, so the Wijnen brothers approached VITO.

First successful drilling in the Netherlands

Building on experiences in the Campine, VITO suspected that the limestone beneath Grubbenvorst could also be suitable for geothermal energy extraction. The researchers mapped out the structure of the deep ground layers. Calculations showed that the substrate had to contain water at between 1500 and 1600 metres with a minimum temperature of 65°C, and also that the flow rate would likely be sufficient. Following the long preparation process, the research team began drilling. The first well was ultimately 2.7 km long and extended 2.4 km down. The result exceeded expectations: a flow rate of over 300m²/hour and a temperature of almost 80°C.

Closed circuit

The result of all this was a new heat source for the Wijnen brothers, while the existing CHP (combined heat and power plant) was no longer required for heat production. Five wells have now been drilled in the greenhouse horticulture site in Grubbenvorst, consisting of three extraction wells and two injection wells. The injection of pumped-out water into the same ground layer from which the water was pumped out, thereby creating a ‘closed circuit’, is a mandatory condition of being permitted to extract geothermal energy in the Netherlands.

Creating a buffer

The major advantage of deep geothermal energy extraction is that performance is not dependent at the same time on the co-production of electricity. If heat demand is lower, such as during a summer’s day, it is possible to fill a buffer vessel and then shut down the pump. This means that no surplus heat is created. That is less obviously the case for a CHP plant, because the electricity production also stops.

Green heat subsidies

There are a great deal of subsidies available in the Netherlands for the production of green heat, which are similar to subsidies in Flanders, and parties are regularly encouraged to submit sustainable energy production projects. “Geothermal energy projects are often highly regarded, so that is of interest for future projects,” says Laenen. However, it should also be said that the Wijnen brothers’ horticulture business comprises over 50 ha of glass, and an investment of 8 million euros is, of course, that bit easier to justify in that case. In Flanders, you would have to be able to cluster several greenhouse horticulture businesses together in order to make an investment of that size.”

Demo project in the northern Campine

A project of this kind is also possible in Belgium, in view of the fact that the same geological layer in which sufficient hot water was found in the Netherlands also occurs in the northern Campine. A short time ago, the Province of Antwerp (Department of Rural Development) launched the idea of a demo project in the northern Campine in collaboration with VITO and the Geel campus of Thomas More University of Applied Sciences. A specific question from a horticulturalist in Merksplas forms the basis of this ongoing initiative.

Viable proposition

It is feasible to develop a project of this kind in that region, though subject to a few conditions. For example, greenhouse-based market gardeners who are all willing to invest and use the heat need to join forces. The existing CHP plants in those businesses also need to be integrated effectively in order to make optimum use of the Flemish subsidy schemes. To do this, a CO2 network would need to be laid in addition to a heating network. This is perfectly feasible with some good will on the part of all the parties concerned and the provision of subsidies by the government. It is now up to the market gardeners in question.

Drilling by VITO

VITO has a great deal of confidence in the potential of geothermal energy, and it has already been operating two bore holes at the VITO sites in Mol. At a depth of between 3,200 and 3,400 metres, the research team achieved a flow rate of 140 to 150 m³ with a temperature ranging between 126 and 128 °C when the water is brought to the surface. In this plant, the flow rate was lower than in Dutch Limburg, but the higher temperature meant that the total heat-generation capacity of 8 MW is more or less as great. This heat will be used from winter 2018/19 on the site of VITO and SCK-CEN (Belgian Nuclear Research Centre) in the existing heating network. From 2019, this heating network is also to be expanded to a number of districts and public buildings in Mol and Dessel. That same heat will also be used to generate electricity at times when there is no or reduced heat demand from the network.

Geology in Belgium

The deep geological layers originated in seas and oceans that used to cover Belgium. The limestone we know is a remnant of the marine organisms that used to live in the sea. At that time Belgium formed part of the Caledonian group of mountains. At the edge of that mountain range, sand and clay were deposited under the sea, and thickly packed calcareous sediment formed. This thick calcium layer was followed later by other layers on top. This limestone still appears on the surface in various sites in Wallonia, where it is extracted as Belgian bluestone. At the Meuse, you can still see this limestone rise to the surface, but it extends deeper into the earth further north. In the south of the Netherlands, for example, the limestone reaches a depth of over 4 kilometres. This limestone is the substrate from which the hot water is being pumped out in the projects described above. A block of bluestone shows a lot of fissures and cracks, which are usually tightly bound together. This enables water transport in this well-known hard stone.


Research Coordinator