BayWa to r.e. and its Netherlands subsidiary, GroenLeven, is developing five pilot agri-voltaic power projects in the Netherlands, where five different crop types are tested: blueberries, red currants, raspberries, strawberries and blackberries.
The largest of the projects – a 2,67 MW solar plant installed on a 3.2-hectare surface devoted to raspberry cultivation – is situated in the Netherlands municipality of Zevenaar, near the Dutch-German border town of Arnhem.
The two companies do not rely on standard PV modules for the project, as in an effective agrivoltaic project, these items are considered inappropriate.
“We used special monocrystalline solar panels developed according to our requirements,” Willem De Vries, AgriPV project manager at GroenLeven told.
De Vries said that the special requirements related to transparency because plants below the panels need to receive adequate light while being shielded from direct sunlight, fog, hail and frost by a foil cover. The sunlight hitting the raspberries should not be too intense, De Vries said.
“We have constructed two separate pilot projects so far, with two types of panels with different degrees of transparency,” he explained. “The crop yield is increasing substantially with increased panel transparency.”
At about 35 kg per panel, GroenLeven used 260 W glass panels which weighed more than their ‘natural’ counterparts. “We applied fairly thick glass layers to feel more confident that the panels can hold off any form of environment,” added De Vries, without disclosing any further technical information.
Passive refrigeration is applied in two separate ways to crops. Next, some of the incoming radiation is absorbed by the panels, second, they set up the modules in such a way that the air will move through them. The natural ventilation means that the environment is warmer under the plants than the ambient conditions and much warmer than traditional foil coverings.
The raspberries are grown with wood, concrete and metal support systems. BayWa and GroenLeven r.e. decided to replace new designs and special panels for such structures. “The mounting systems were specifically developed for this project, too, and it is the first time it has been implemented,” added De Vries.
GroenLeven said the supporting structures have been built such that heat is carried away passively easily. “We learned that the exact percentage of light is very significant, but we also learned that the atmosphere is structurally better under the solar panels than under the conventional plastic cover,” he said. “We can see this in our surveillance now.
The temperature below the panels is 5 degrees lower on hot days than under the plastic coverings, and even 2 degrees lower than in normal conditions.
This dissipation of heat is good for the plants. The temperature under the panels is higher at night, as they hold the air better than the plastic covers. This result is shown to be beneficial to the plants. “The humidity under the panels is also more stable than normal coatings,” De Vries said.
Farmers often benefit from the new support structures, as they are said to be less vulnerable to strong winds, so less or no labour is required compared to traditional foil-based growing systems.
Considerations on costs
Although the two companies have yet to provide information on the costs of the project and the Levelized energy prices, De Vries said farmers will benefit financially. We can save on support structures already built into the solar mounting systems.
“Of course the costs of AgriPV installations are considerably higher at this point than for ground-mounted installations,” De Vries said. “But due to practice, improvements and a supply chain that is accustomed to our unique requests, those will fall.”
When the suppliers have obtained enough orders, the two companies expect the understructure and the panels to decline in size.
According to the developers, the pilot agrivoltaic projects are increasing crop yields but also quality. Farmers may be able to tolerate lower yields if the quality and price are better, or if the overall quality of output improves at lower costs.
The Raspberries can withstand shade. “We have also started pilots with several other berries this year and we strongly believe that all crops will have their own needs and will react differently to the circumstances generated by agrivoltaics,” Schindele said. “Therefore, getting experience with many crops is significant.”
Source – here