With the signing of the Energy Transition Covenant Greenhouse Horticulture 2022-2030, the greenhouse horticulture sector is showing its ambition to be both economically profitable and climate-neutral in 2040. One-third of Dutch horticulturists already use a form of solar panels, as it is one of the most sustainable sources of energy for horticulture, and twenty percent plan to invest in them, according to research by AgriDirect. BOAL Systems saw this trend as well and has been diving deeper into the discussion regarding the use of solar energy in horticulture.
To ensure that the climate and energy transition in the sector continues, the dependence on fossil energy sources must be reduced, and the contribution of clean energy must grow. This means that if greenhouse growers want to continue practicing their craft, smart measures are needed. Switching from glass cover systems to solar cover systems could be such a smart measure. But what does this switch involve, and what does it mean for cultivation?
For most crops, a one percent decrease in light level results in an equally one percent decrease in crop yield, according to research by Wageningen University & Research. Although some call this light rule debatable, commissioning a greenhouse cover system of solar panels does have the necessary impact on crop production due to the reduced light entering the greenhouse.
One possible solution for this is supplemental lighting with artificial light, but this requires an additional investment. Another alternative is to switch to crops more suited to semi-shade or deep shade, such as spinach, kale, cauliflower, herbs, berries, blackberries, or bedding plants.
Local development plan
When switching from a glass roof to a solar roof, it is also important to check beforehand whether this fits into the municipality’s local development plan. The local development plan dictates what activities are allowed in places within a municipality. A municipality may find that such a modification changes the function of the greenhouse: from a cultivation activity to an energy-generating activity.
To determine whether such a modification is allowed under the local development plan, it is important to check whether this plan includes stipulations that say something about energy generation and solar panels on agricultural sites.
Types of panels
When it comes to solar roofing, there are two types. First, there are the traditional and mass-produced 30- or 35- millimeter framed panels: the regular market offering. The thickness of these panels requires a specifically designed mounting system with appropriate roofbars, a specific ridge, and a gutter. Second, are the 4-millimeter framed panels. At the location of the overlay, the thickness of this panel corresponds to the thickness of horticultural glass, which means it can be mounted like a glass panel.
The advantage of the 4-millimeter system is that the complete set of profiles used for 4-millimeter horticultural glass can also be used for the solar roof. The disadvantage is that such panels are somewhat more expensive than traditional panels, but this investment is largely recovered through less labor in assembly.
Rainwater enters the gutter, flows to a head gable or column drain, and can cover the bottom part of a solar panel. Without smart regulation, a solar roof is as efficient as the least efficient cell. So a choice must be made between accepting some contamination – from sand in the rainwater, for example – on the lower cells or placing extra glass just above the gutter.
The latter provides a slightly less useful surface area for the solar roof, but there is also less pollution as a result. Usually, the choice is made to cover an entire roof side with solar panels, and thus no underlighting is used. This solution allows for the maximum usage of the operative surface area, and investment in stacking profiles and odd-sized windows is avoided.
With the energy transition, the share of electricity in energy use is increasing in a lot of industries, causing blockages in the electricity grid (grid congestion) to become an issue in more and more areas. The switch to solar energy means that a lot of energy will be pumped into the electricity grid, so it’s important to check with the energy supplier whether there is sufficient transport capacity available from the location of production to feed into the electricity grid in advance.
If half of the energy generated is lost, this is obviously very inefficient, and it is questionable whether the investment will pay off. Waiting for new power lines to be installed takes a long time. A possible solution is a battery system that allows clean power to be stored so that the grid is not burdened. This solution may require additional investment but may be worth exploring.
For more information:
Marie Curiestraat 3, 2691 HC
‘s-Gravenzande, the Netherlands
Tel.: +31 (0) 174 316 100