Green Energy for Sun-ripened Cucumbers and Tomatoes


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Greenhouse industry sets a whole new dimension and a new trend for large-scale solar thermal energy.

A true frontrunner in the greenhouse industry

In the large greenhouses of Østervang Sjælland in Varpelev, Denmark, a whole new dimension has been set and maybe a new trend for the concept of solar thermal since such large-scale solar heating systems in Denmark have so far been associated with district heating.

Growing vegetables in greenhouses in Denmark requires energy and heat – plenty of heat. Therefore, the heat exchange station at Østervang Sjælland can be compared with a medium-sized power plant.

Annually 3,500 tons of vegetables are produced in Varpelev, Denmark – mainly small and large cucumbers, snack tomatoes, red and yellow tomatoes and Coeur de Boeuf tomatoes. And Østervang Sjælland is ambitious to reorganize and optimize the energy consumption so that the use of fossil fuels can be reduced. A 2020 plan foresees a 20% reduction compared to 2010. The new and stricter rules introduced in 2013 of course also have been an important incentive to think about energy optimization.

The solar energy is stored for the morning hours

The 14,112 m2 solar collector field can produce up to 60 MWh on a sunny day, but since the energy must be used early the next morning, it is stored in the 4,800 m3 large storage tank that can accommodate up to 5 days’ full solar production. This, however, should not become necessary with the expected consumption in the large greenhouses.

Reduction of chemical disease control

When the control of temperature and humidity is properly managed, the use of chemical disease control can be reduced significantly, thereby making it possible to produce healthier and more environmentally friendly vegetables. The technique of controlling heat and moisture is used by most major players in the greenhouse industry, but usually, the heat comes from boiler plants based on coal or gas. The new feature in the greenhouses in Varpelev is that the heat is produced as 100% fossil and CO2 free energy, due to the implementation of solar collectors. This helps provide a more environmentally sound end-product and makes a significant contribution to achieving the 2020 plan. It is a true pioneering project introducing ”green” energy and at the same time means a substantial economic saving for the company.

Optimal climate control for growing vegetables

One might think that there would be enough solar heating for the plants, as they are grown in large greenhouses, but that is not quite the case. One of the secrets behind the efficient production of vegetables in Danish greenhouses is the control of the climate around the plants.

They should not just be warm, round the clock; the heat must be dosed, so the plant’s natural life cycle is encouraged and enhanced. There must be periods of lower temperatures at night when the sugars draw from the plant and into the fruit. In the morning when the sun comes out and the temperature rises, heat must be added close to the plants so that the evaporation from the soil and the air do not condense on the plant and fruits, thus providing a breeding ground for fungus and other plant diseases.

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