News - April 4, 2019

A gas-free greenhouse

Roelof Kleis

Greenhouse horticulture uses a lot of fossil energy. With its brand new All Electric greenhouse in Bleijswijk, WUR wants to showcase an alternative.

text and photo Roelof Kleis  illustration Annet Scholten

Series: Experimenting for the climate

The Netherlands aims to cut its greenhouse gas emissions by 49 per cent by 2030, compared with 1990. How we are going to do that is to be laid down in a comprehensive Climate Agreement. Ahead of that, ministry of Agriculture funds are being used for numerous experiments in emission reduction. WUR is coordinating these pilot projects for the Agriculture and Land Use sector. Resource is currently taking a look at these experiments in four numbers. This week, episode 4: greenhouse horticulture.

Manager of the Greenhouse Horticulture business unit Sjaak Bakker in the brand-new sustainable demonstration greenhouse.
Manager of the Greenhouse Horticulture business unit Sjaak Bakker in the brand-new sustainable demonstration greenhouse.

There are several large demonstration greenhouses at Wageningen Plant Research’s Greenhouse Horticulture business unit in Bleijswijk. They all look the same from the outside, so the ‘All Electric’ at the far end of the site doesn’t jump out at you. But this newest addition to the business unit is different from the other greenhouses. It is state-of-the-art as far as sustainability is concerned, explains business unit manager Sjaak Bakker. A demonstration greenhouse that offers the sector a peek into the near future.

Light amd warm

‘At the beginning of 2018, we were asked by the ministry of Agriculture, Nature and Food Quality to build a greenhouse that is as sustainable as is currently possible,’ explains Bakker. It is easy to see why. Greenhouse horticulture uses vast amounts of light and heat. The lighting requires a lot of electricity and the heating and dehumidifying are still mainly gas-fired. So the environment can benefit greatly if greenhouses are made more economical and gas-free.

It did not take long for project leader Frank Kempkes and his team to design, commission and build a greenhouse. ‘A demo that uses no gas and as little energy as possible, and has zero emissions in terms of nutrients and crop protection products,’ says Bakker. The building costs: a mere 2.3 million euros.

The greenhouse is not completely finished yet. Inside, workers are busy setting things up. Bakker: ‘It is a miracle, really, that it is already built. There is a lot of building going on in the greenhouse sector. We started building in September and in another week the plants will be going in.’

Strawberries and freesias

In consultation with the ministry, the designers decided to make the greenhouse suitable for crops than usually require 10 to 25 cubic metres of gas per square metre per year. There is a reason behind this decision to go for the middle of the range, in terms of heat consumption. Bakker: ‘A lot of research has already been done on crops such as tomatoes, paprika, roses and chrysanthemums. These are crops of the type that requires a lot of heat, about 30 to 50 cubic metres of gas per square metre per year. And that is logical: if you want to save energy, start with the big energy guzzlers. That’s why we are now looking at the middle of the range.’

In the All Electric greenhouse there are experiments with strawberries, gerbera, freesias and pot anthurium. ‘Crops that are representative for a particular group and are economically important,’ explains Bakker. ‘Growing strawberries under glass is on the rise. Gerbera is a typical example of a mid-range decorative plant, anthurium represents pot plants, and the freesia is specific because it requires soil cooling and is still grown in the ground, which makes it harder to limit emissions from nutrients.’

Volledig gesloten

Each of the four crops has its own cultivation system. So in fact, All Electric is made up of four different greenhouses, taking up 350 square metres each. The pot plants stand on tables, the gerberas in gullies on the floor, and the freesias in trays. The strawberries hang in hoistable containers in order to make the best possible use of the available surface.

All Electric is unique in its concept and the combination of applied techniques drawn on, explains Bakker. ‘The greenhouse is completely closed. It has a 100 per cent recycling system for water and nutrients. Water that the plants do not use is captured, purified, mixed with clean water and nutrients, and reused. The greenhouse is lit with efficient LED lighting, and natural light comes in through special glass that creates a diffuse light distribution in the greenhouse. The right light conditions are created using double screens which are adjustable independently of each other.’

Entrepreneurs are involved so that results are relevant to operations


The same screens help keep the heat in as much as possible. That is positive, but a closed system also traps moisture so rising humidity is a problem. ‘Traditionally, the air vents are opened to ventilate the place,’ says Bakker, ‘but then you lose the heat too.’ This problem is solved in the new greenhouse with a dehumidifier/ heat pump which retains the heat and extracts the moisture. ‘That may cost electricity but it is still more energy-efficient than opening the window.’ The name All Electric is due to the use of this electric pump, which makes the greenhouse gas-free.

So the greenhouse is not fully climate-neutral? ‘It all depends how you define that,’ says Bakker. ‘We don’t generate the electricity ourselves, but use electricity from the net. The emphasis in this project lies on minimalizing CO2 emissions. The system runs entirely on electricity.’

Army of insects

The greenhouse is also full of measuring equipment. All the flows of water, electricity and nutrients are monitored precisely. At the same time, the use of crop protection products is kept to a minimum. The plants are protected by a ‘standing army’ of insects: biological pest control. This army of predatory insects is constantly on standby in the greenhouse.  The challenge is to keep these predators alive when there are no pest insects present. By feeding them, for instance, or by installing special host plants on which they can survive.

The project in Bleijswijk is led by four groups of growers – one for each type of crop. This is essential, according to Bakker. ‘The entrepreneurs are involved from the start so that the result is relevant to operations management. That is the strength of our organization. It is my experience that this enables you to push the boundaries. You’ll see that parts of this greenhouse will be in use in the sector in about five years.’