Greenhouses do not have to be heated in the summer. In fact, there is often even a surplus of heat, especially if geothermal energy is being used. With that surplus it is possible to heat the water for indoor fish farming. The Greenhouse Horticulture Business Unit of Wageningen University & Research is investigating - together with European partners - whether geothermal sources can be utilized better through combinations of greenhouses and fish farming (so-called aquaponics).
A constant water temperature is required for fish farming all year round. Supply and demand are less constant in greenhouse horticulture: relatively much is heated in winter, and there is a surplus in summer. In addition, there are more and more cultivation companies with a geothermal source. This creates an even greater surplus in the summer. Selling that heat could provide a different business case for geothermal sources.
Recirculating aquaculture system
That is why the greenhouses of the WUR in Bleiswijk now have an advanced fish farming system, a so-called recirculating aquaculture system (RAS). The largest tanks contain around 10,000 liters of water. Several thousand fish live in it. Walleye, to be precise. This species is very suitable for consumption and is becoming increasingly popular, both among consumers and growers. If the heat from the greenhouse can be used for indoor fish farming, then that probably also has a positive effect on the business case of aquaponics.
WUR investigates the effects for about a year. How much heat can be exchanged, and how much heat is saved with it? For this, the researchers simulate the residual heat from the greenhouse (of approximately 35°C) and from a geothermal source (approximately 80°C).
WUR carries out this research in collaboration with partners from Iceland and Slovenia. The heat requirement for algae production and food processing processes is also being investigated to investigate the potential of circular food systems for the use of geothermal energy. Funding for the research comes from the European GEOTHERMICA - ERA NET Cofund Geothermal.