Better design of solar parks needed to maintain soil quality

TNO has been asked whether the many east-west oriented solar parks which are planned can be designed differently, thereby preserving soil quality while delivering the same yield as south-facing parks. A crucial factor is the amount of sunlight that reaches the ground between and below the solar panels. In many east-west solar parks, the panels are placed close together and cover almost the entire plot, which means that soil quality deteriorates over time. If a solar farm is then cleared after 25 years according to the current standard, there is a good chance that the soil will be difficult to use for agriculture or environmental development. It will then take a great deal of time and effort to restore the soil quality that existed before the solar farm was constructed.

Better distribution of light

The TNO study shows that a great deal can be gained by ensuring that light is more evenly distributed. Improvements are especially possible in the parts of the solar park where there is little light beneath the panels. TNO has the software tool BIGEYE that calculates both the yield of solar panels and the incidence and intensity of light below and alongside the panels in a solar farm. Two south-facing set-ups from a study published earlier this year by Wageningen University & Research (WUR) were examined in more detail and compared with conventional east-west systems. In the calculations, TNO experts looked at variations in the degree of coverage, the angle of the solar panels and the space between the panels.

Bifacial panels

Both the business case and the connection to the grid make east-west oriented solar parks attractive in the Netherlands. With this in mind, TNO has calculated two additional variants: one with standard solar panels and one with panels that harvest solar power on two sides (bifacial). These new panels are semi-transparent and yet produce a higher yield because they also convert the reflected light from the ground into electricity via the back of the panel. A 77% coverage design with semi-transparent, bifacial panels scores better in terms of the effect on soil quality than south-facing standard panels with 53% coverage. As a result, almost 100% of the soil receives sufficient sunlight at a higher degree of coverage. According to the researchers, the desired adjustments to the design are possible without affecting the business case.

Economically sound

For landowners, public authorities and project developers, the study offers many opportunities to take a different approach to the design of solar parks. TNO has not only calculated the impact of various set-ups on ground-level radiation but has also established that the desired design adjustments are economically feasible, particularly in comparison with solar parks that are currently deemed safe. Furthermore, at the end of the solar park's life, the landowner will own valuable land which remains fertile. TNO recommends the establishment of criteria for ground irradiation under and between solar panels.

Collaboration with WUR

Commissioned by the Central Government Real Estate Agency, the TNO report is in line with research published earlier this year by WUR on the effects of solar parks on biodiversity. WUR examined 25 solar parks in order to determine which types of parks have what sort of effects on soil, vegetation and species diversity, among other things. An overview was made of the type of solar panels, their amount, the coverage, the distance between panels and the incidence of light. TNO and WUR have been collaborating for some time in the Nationaal Consortium Zon in Landschap (Solar in Landscape), which focuses on spatial quality, biodiversity, multifunctional land use and grid integration in the establishment of solar parks.