Two-sided panels are well suited to agrivoltaic installations
Published on Sunday 23 January 2022 | Article n°390
Dutch researchers have defined an optimised topology for agrivoltaic projects using bifacial panels. In their view, the advantages of these panels are greater when they are integrated into the roof.
in projects mounted on stilts. They are then raised more than 2 metres above the ground, allowing light to be absorbed by the rear PV face as well. This applies to light-demanding crops, since the amount of irradiation incident on the ground needs to be abundant, which works well with the bifacial panel.
Bifacial panels are not recommended for all agrivoltaic projects in the world, such as mushrooms, which need mono-facial panels because they require intense shading.
As solar installations move closer to the equator, the advantages of bifacial agrivoltaic projects diminish, particularly for crops that can tolerate shade.
The researchers studied the most favourable orientation for fixed bifacial panels: north-south, east-west and east-west vertical. They found that panels with an east-west orientation offer a more even distribution of light on the ground, allowing crops to grow evenly. The south orientation is recommended for summer crops, as they cast thick shadows and are associated with increased electricity production.
The east-west position combined with extensive translucent covers may be the right option for high-value crops, such as berries and organic farming, as it can provide protection against adverse weather conditions such as hail.
The north-south orientation of bifacial panels can provide up to 39% more energy than mono-facial panels. Panels oriented east-west in wings or east-west vertical have a higher efficiency of 18% and 13%. The vertical east-west placement is more suitable for permanent crops, while the vertical north-south position requires shade-tolerant plants during the summer, as electricity production takes priority. In fact, the E-W position combines the best of both worlds: light is distributed evenly, and crops are effectively shaded at midday.
Finally, by adjusting the spacing of the cells and therefore the transparency of the panels, the rate of photosynthesis in the shade has increased significantly, promoting crop growth, even in the climate of Boston (USA). Ultimately, this customised topology will outperform the others when it comes to growing high-value permanent crops, particularly in climates where light conditions are low and/or adverse climatic events occur.
In agrivoltaics, albedo is difficult to calculate. It is modified by the optical properties of the surrounding landscape and by the photovoltaic configuration adopted. The albedo of the soil will also be crop-specific, which intensifies seasonal variations. Crop architecture - canopy height, leaf area index and leaf arrangement - will greatly influence the amount of light reflected from the ground.
PV Magazine, 21 January 2022
Editor's note With this study, we are beginning to get a better idea of the orientation of panels on plants. But it is not enough to convince people. To be convinced of the benefits of agrivoltaics, we need to know the final contribution of cultivation + energy production compared with the production of electricity.To be convinced of the benefits of agrivoltaics, we need to know, firstly, the final contribution of the crop + energy production compared with production in the open air and, secondly, we need to include the cost of installing the panels high up in the calculations. Ultimately, it is necessary to know what the farmer receives in surplus or less in his crops with a PV installation and therefore to determine in how many years the possible surplus of his production amortizes the original cost of the installation.