There are high expectations for energy-producing greenhouse. A greenhouse is a structure with a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall.

These structures range in size from small sheds to very large buildings. The glass used for a greenhouse works as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it.

The Huisman nursery in Bergerden (between Arnhem and Nijmegen) is testing an energy-producing greenhouse. With the help of innovative heat exchangers, solar energy is ‘harvested ‘ in one section of the greenhouse. The surplus heat is stored in aquifers (underground layers of water-bearing material), and can then be used to heat the greenhouse during the winter month.

“I was never happy about it,” explains Stef Huisman. “In summer you have to invest heavily to get rid of the excess heat from the greenhouse, and in winter it costs you a fortune to heat the greenhouse with expensive natural gas. There had to be a solution.”

Although the grower identified the tremendous future potential of an energy-producing greenhouse early on, he had to wait a long time before his idea could be put into practice.

Fully Sealed Greenhouse

Ten percent of the greenhouse area is used for generating energy, while another 10 percent is used for control purposes. The energy-generating section of the greenhouse has a zigzag roof, which provides the maximum levels of light and good insulation, thus making optimal use of solar energy.

The heat absorbed by the greenhouse is transferred to water through FiwiHex heat exchangers, and is then stored in an aquifer from where it can be pumped out in the winter months.

This same system can also be used to dehumidify the greenhouse.

Huisman said, “The greenhouse can now remain fully sealed, without losing carbon dioxide and insects are kept out. This means you can drastically improve the quality of your products, which gives you a competitive edge.”

Idealist

Huisman had always believed in the principle now being tested at his company, but for a long time he was in a minority. “You’re just an idealist “ people would tell him.

A greenhouse that generated energy rather than consuming it seemed inconceivable. It took Huisman a long time to make people understand the possibilities and the need for this innovation. He also tirelessly lobbied the government to push his idea onto the agenda.

“And of course you also run into technical problems at the beginning. A prototype like this always suffers from teething troubles, but we have managed to resolve most of them,” he said.

Final Challenge

Huisman is convinced that the energy-producing greenhouse has a future. “But,” he adds, “the story doesn’t end here. It’s a clever idea, but there are certainly even cleverer ideas out there. The challenge is to create a greenhouse that transforms solar energy into electrical energy.”

Huisman envisages that his energy-generating greenhouse will be used on a larger scale in the future. However, he does acknowledge that certain areas still require more work.

“If all greenhouses switched to this system we’d have a problem. Then we’d have a heat surplus which we wouldn’t know how to deal with,” he said.

The innovative grower welcomes the fact that the sector has embraced renewable energy, and he is interested in the possibilities of geothermal energy, biofuels and plant varieties that use low levels of energy.

“But I think that making better use of the sun is truly the way forward and in my view this offers the brightest prospects,” he said.