Solar Magazine – The Dilemma

Will partially transparent and bifacial solar panels be the norm in field setups in 5 years? Solar Magazine discusses this dilemma with Kay Cesar of TNO. ‘If we take soil quality seriously, it will go in that direction.’

Kay Cesar is Head of Advanced Solar Parks, PV Modules & Applications at TNO Energy Transition. According to him, there is plenty of room to improve the design of solar parks so that the production of green electricity does not happen at the expense of biodiversity. In this context, TNO has calculated soil-friendly variants on the basis of a recently published standard for soil irradiation, where the best score is an east-west arrangement with two-sided, partially transparent solar panels.

Is the preservation of soil quality receiving sufficient attention in the sector?
‘Parties applying the industry code of conduct, Sun on Land, commit to a minimum of 25 percent uncovered surface of a solar field. With current knowledge, this is in principle sufficient to maintain soil quality. But if that space is mainly about the edges of a park and roads, and the solar panels themselves are close together, it will result in a completely depleted soil after 25 years. In east-west installations, coverage rates of 90 to 95 percent are no exception on the part where the solar panels are installed. That’s worrying. ‘

East-west setups are becoming more and more popular …
“At the moment, it is about 30 percent of the solar parks, but that share is growing. Southern squares are still being built, but the driving force from the market to the east-west is strong. Of course, it has to do with money. Basic prices are rising, basic amounts in SDE ++ are falling, solar panels are becoming more expensive … We want to avoid large peak loads in connection with the connection to the electricity grid. The solar panels are also being laid more and more flat, so that more ground surface is shielded from sunlight. ‘

What do we really know about solar parks, soil quality and biodiversity?
‘Not very much yet, but more and more. A lot of research is done, for example by Wageningen University & Research (WUR). However, we do not have the luxury of studying the effects of different designs in detail over their entire lifetime if we take soil quality and biodiversity seriously. We must act now. And it’s actually very simple. The earth needs light, water and food as an energy source for life. If you visit a solar park and you do not see a single plant under the solar panels, you know that something is wrong. WUR looked at the gradations in the vegetation of 25 solar parks in the Netherlands. TNO used the data, among other things, to arrive at a soil-friendly design with east-west orientation. This is important because you sometimes want to make use of this for landscape integration. Then it is good to know that it is now also possible, while preserving the soil quality. ‘

How do they look?
»According to WUR, the most soil-friendly solar parks with a southern installation have a solar cell density of about 50 percent. We calculated earth-friendly east-west setups. In our best design, the one with partially transparent bifacial solar panels, we arrive at a coverage ratio of 77 percent, where the soil receives sufficient sunlight to maintain soil quality. This will result in a solar park with 40 percent more solar panels and a quarter higher power yield per. hectares than the safe reference design with south-facing standard solar panels. You sacrifice energy production per solar panel, partially translucent solar panels are a little more expensive per watt peak, but you can place more. The cost gap between semi-transparent, bifacial and standard solar panels has recently narrowed, improving the business case. ‘

Will these partially transparent solar panels become the norm in field setups in the Netherlands?
“If we take soil quality seriously, it will definitely go in that direction for east-west solar parks. So it starts with a social awareness of the importance of soil quality, and in fact to take this as a general guideline for development, which of course must also be profitable. In this light, our soil test can be seen as a start on the creation of a new standard. At the same time, the share of bifacial solar panels will still increase globally, to 60 percent by 2030, the ITRPV roadmap predicts. This will also drive the Dutch solar panel market further in that direction. The standard will in any case be that a project developer integrated will consider the possibility of bifacial and partially transparent panels in the design of future solar parks. ‘

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