The maximum amount of light and optimal energy savings
At the end of 2019, Kwekerij Moors in Asten took a new five-hectare greenhouse into use. To optimize the light penetration into his crop, pepper grower, Rob Moors opted for diffuse glass. At the same time, he invested in two Luxous 1147 FR screens from Svensson. The latter turned out to be the right choice: Moors optimally saves energy while still guaranteed a maximum amount of light in his greenhouse.
Nursery Moors currently comprises 19 hectares of sweet peppers, spread over locations in Asten and Someren.
"In Asten, we have 13 hectares of greenhouses in which we grow red peppers," says Rob Moors. "Our location in Someren has 6 hectares and is reserved for the cultivation of yellow peppers." The last expansion took place in 2019 when five hectares were added in Asten.
This was done at the request of customer Van Oers United, who needed extra red peppers.
We naturally wanted to furnish the new greenhouse with the latest techniques. Since light is a determining factor in greenhouse vegetable cultivation, we also decided to explore diffuse glass possibilities. More and more pepper companies are investing in this.
The fact that the light penetrates deeper into the crop results in higher production. But there are also disadvantages: due to the AR coatings, the light transmission is higher, and you also get more UV light.
This means that you have to screen earlier and more often in the summer to prevent fruit burning. We also heard this from fellow pepper growers, who had previously invested in the diffuse glass.
Most translucent energy screen
To protect the crop against too much light in the summer months, Moors opted for diffuse glass with a single-sided AR coating on the inside of the glass.
"This allowed us to chalk the glass - which has a haze factor of forty percent - if necessary, to shield the excess light in the summer. So we knew that we probably had to screen more and earlier in the summer months. That is why an energy screen with a high light transmission was crucial. For this reason, we chose the Luxous 1147 FR screen from Svensson."
Luxous 1147 FR is, according to Svensson consultant Ton Habraken, the most translucent energy screen on the market.
"This screen lets in much light. Indirect light, according to our measurements, there is a light transmission of 89 percent. The NEN 2675: 2018 - this is the standard for objectively measuring the light transmission of greenhouse covering materials and climate screens - shows a light transmittance of 85 percent indirect radiation. However, even more, important is the hemispheric transmission, the amount of light in the greenhouse in the winter sunshine. Our measurements then show a light transmission of 81 percent; the NEN protocol shows the transmission of 75 percent in this case. Due to its high light transmission, Luxous 1147 FR, which has now been on the market for a few years, has grown into the standard energy screen in the cultivation of peppers, cucumbers, tomatoes, and strawberries."
Production increase in spring
The choice made pays off, especially in winter and spring.
"Thanks to the Luxous 1147 FR screens, we save maximum energy in winter, even a little more than with our other energy screens. At the moment, I cannot give precise savings figures yet," says Moors.
"At the same time, the plants receive more light. This results in a fresher and more vital crop. This also allows us to maintain a slightly higher 24-hour temperature and thus accelerate crop growth. This contributes to higher production; we get just a little more out of the crop. Until the summer, we had a head start in terms of production. But it is still difficult to substantiate this with concrete figures; for that, we need to gain more years of experience. We also actually see throughout the year that the crop is a bit more active. This results in a greater water absorption; after all, a more active crop evaporates more."
As Moors feared, the diffuse glass does result in too much light in the greenhouse in the summer months. This means that he must close his screens earlier to avoid burns.
"In our greenhouses with clear glass, the screens do not close until the afternoon. In the greenhouse with diffuse glass usually already in the morning. We focus on fruit temperature. When it rises, we first start venting a little harder. If that works insufficiently, we close the screens. This usually happens at a fruit temperature of 43 degrees. Because we have to screen more, the production increase will level off in the summer months."
Summer screens on the rise
Habraken indicates that - since new diffuse glass types with AR coatings often result in too much light during the summer months - more and more pepper growers opt for a Harmony summer screen with an open structure instead of a second energy screen.
“Then it is not the glass, but the screen that provides the desired diffusion. Pepper growers often combine such a screen with clear glass with a single or double AR coating to ensure the maximum amount of light in winter. And in the summer, they close the summer screen when necessary to distribute the surplus light over the crop in a high-quality manner. Monitoring in practice with a thermal imaging camera shows that this reduces the fruit temperature. For that reason, I expect that summer screens in peppers will continue.”
Moors also sees the potential added value of such a summer screen.
“But when we started investing, there was little experience with these summer screens in sweet peppers. That is why we have made the outlined choices. ”
The first year, Moors is satisfied with the combination of diffuse glass and a double Luxous 1147 FR screen. However, there are points for improvement.
“We are generally positive about the effects of diffuse glass, only in the summer, the light is just a bit too bright, as mentioned. For that reason, we will apply a coating to the greenhouse roof next summer. Hopefully, this will reduce the need to shield us from too much radiation to allow more light into the greenhouse and further increase production in the summer.”
Moors does not dare to say whether he would choose diffuse glass again for new construction.
“We need an extra year of experience for that, especially since we are still struggling with the excess of light in the summer months. In any case, I am more than satisfied with the Luxous 1147 FR screens: they are beautifully bright, but again do not let too much light through in the summer. There is, therefore, no question of fruit combustion. When light is the limiting factor in the winter, we bring in a maximum amount of light. In short: the Luxous 1147 FR screens are the ideal combination of a maximum amount of light and optimum energy savings.”
Moors indicates that it would be nice if the Luxous 1147 FR screen would allow a little more moisture in the fall.
“But that is difficult because we want to have as much moisture as possible in the greenhouse during the first three months of cultivation. This provides a better climate and faster, more optimal growth. On the other hand, in the autumn, it is nicer if the screens allow a little more moisture through so that there are fewer problems with mildew. And we prefer not to pull a crack to prevent a cold. This autumn, we tackled this problem by screening with one instead of two screens in the autumn.”