‘We should not depreciate the closed greenhouse’, ‘Greenhouse growers should rely less on feelings and more on knowledge’ and ‘In the greenhouse sector of 2050 gas is no longer relevant’. These were some of the remarkable statements that were made at the well-attended EnergiekEvent 2016 in Bleiswijk, where the 10th anniversary of Kas als Energiebron was also celebrated.

Looking back, Kas als Energiebron (Greenhouse as a Source of Energy), the innovation and action programme for energy efficiency and sustainability in the greenhouse horticulture sector, was found to be successful. The energy efficiency of the Dutch greenhouse growers has increased significantly, while the energy sources are becoming more sustainable. Especially thanks to geothermal and residual heat, wind energy, (semi-)closed greenhouses, diffuse glass, LED lighting and – the manual is in need of a reprint – Next Generation Cultivation.


The best news of the EnergiekEvent was that the increased energy efficiency does not affect the quality or production. But it does require more data, knowledge and insight of the growers. “Before, there used to be one measuring unit on each hectare. In the future we want to change this to smaller units. Maybe even to micro-controllers for every plant, not only for the production, but also for the quality. For example, think of LED lighting to enhance certain plant components,” says Sjaak Bakker, manager of Wageningen UR Greenhouse Horticulture.
Bakker outlined a future in which electricity will play a leading role. “We are rapidly moving towards an all-electric situation. Just look at electric cars, batteries and what’s happening in LED lighting. They are already thinking about lighting through foils or glass cells.”
Our CO2 supply should also be different in 2030 or 2050, Bakker said. “If we no longer burn gas in the future, where would we get our CO2 from? An example might be extracting CO2 from the air.”

Closed greenhouses

Next Generation Cultivation is being succesfully applied in various crops, including tomato and gerbera. An estimated 15 to 20% of the Dutch growers is using this method. A lot of knowledge has been gained in closed greenhouses and during previous research, Bakker said. “In Next Generation Cultivation many things that were already developed have been put together: think of temperature integration, research on screens, air movement, etc.”
The closed greenhouse is disappearing, it seems. But Wilco Wisse, chairman of Kas als Energiebron and staffmember of Lans Tomaten, thinks that closed greenhouses should not be depreciated. “We ourselves also have an Optima greenhouse of 1.5 hectares and we know better than anyone how difficult it is to make profits with it. It is actually a huge solar collector though, it stores excess heat of the summer and supplies it in the winter. Therefore, we should not depreciate the closed greenhouse.”

Sustainable future

Leo Oprel, currently working as a policy advisor at the Ministry of Economic Affairs – who is considered as the founder of Next Generation Cultivation at Wageningen UR – outlined a sustainable vision of Dutch horticulture, in which:

  • new greenhouses will look very similar to existing greenhouses
  • gas has been replaced by sustainable electricity and heat
  • virtually no chemical pesticides are used
  • the use of CO2 for growth is limited
  • knowledge is crucial
  • climate control will include energy and ventilation management
  • heat exchangers will become commonplace to transfer energy from the moist greenhouse air to the incoming drier air
  • cultivation is done with more humidity, with a very homogenuous greenhouse climate
  • light is the key for temperature control
  • the diffuse greenhouse roof transmits more light and there are more screens hanging above each other
  • super translucent greenhouses will determine the production – and the existence – in the winter
  • light will be flexibly captured above a certain level in the summer and will be available for energy storage
  • excess radiation is immediately absorbed without the greenhouse air heating up too much
  • assimilation lighting is used on the basis of the requirements of the plant
  • the artificial light is also dimmable because it works with direct current
  • the heat requirement is reduced to 10 cubic meters of gas per m²
  • geothermal energy and heat pumps with heat/cold storage supply the residual heat
  • the backup will consist of batteries
  • offices and industrial buildings supply additional electricity with roof-integrated solar panels
  • windmills are a regular appearance in horticultural areas
  • proud entrepreneurs have created a sustainable future!

Kas als Energiebron, the innovation and action plan for energy efficiency and sustainability in greenhouse horticulture of LTO Glaskracht Nederland and the Ministry of Economic Affairs, will continue until the end of next year. Both the greenhouse horticulture industry and the government want to continue with the program. The ministry of Economic Affairs wants to maintain the 50/50 cost sharing – but is still negotiating with LTO.
At the end, the participants visited the workshops and greenhouses at Wageningen UR/Delphy Improvement Centre, where they were informed of the latest research.

Text and images: Mario Bentvelsen