In September 2020 there were 229 solar parks in the Netherlands, and the number is growing exponentially. “Up to 2050 we foresee the need for at least 30,000 ha of solar parks on the land,” said ecologist Friso van der Zee. “In this densely populated country and given the great loss of biodiversity, we can’t afford to ignore clever functional combinations. But then we have to know what the effects of various designs and forms of management are on biodiversity, the soil, the landscape and even food production.”

Cutting and removing

According to the researchers, the biggest obstacle to high biodiversity on former agricultural land is the fertilised soil. Only a few plant species, such as English ryegrass or stinging nettles, are resistant to a lot of fertilisation and nutrient-rich soil. To increase biodiversity on former agricultural land, the nutrient richness must decrease so that more plant species have the chance to grow. In the first five years this can be accomplished by cutting and removing the cuttings. The highest biodiversity was measured in parks that are mown and where the cuttings are removed. But almost all of the solar parks use the shredding method, and the cut vegetation remains lying on the ground.

Choose a southern orientation

The orientation of the solar panels is also a determining factor for biodiversity. Solar panels usually lie on ‘tables’ in a field. Friso van der Zee: “Research has shown that the more room there is between these tables, the greater the biodiversity. A high number of plant species is possible starting from about two meters between the rows if well managed.” The researchers found that the biodiversity under the panels was lower than between them where fewer different types of plants grow. This is especially true of east-west orientations in which the amount of light under the panels is very low. “Choose a southern orientation where possible,” Van der Zee advised.

Municipalities: make demands

“Developers of solar parks are quick to present themselves as green and good for biodiversity. But biodiversity doesn’t just happen by itself,” Van der Zee emphasised. “More attention to and knowledge of biodiversity are needed during the design and management.” The researchers think that municipalities should play a more decisive role in this. In general, the municipality is the organisation that grants the permit to build a solar park. As such, the municipality should request a nature plan and make demands with regard to management. The municipality can also request that the nature values be monitored prior to and after the construction of the park. This will increase the researchers’ and the project developers’ knowledge of biodiversity.

Research on the effects on animals and soil

In the research, plant species were studied. Although the diversity of plant species is related to general biodiversity, it is not yet fully clear what the effects on birds and insects are and how the various constructions affect, for example, the carbon stock in the soil. This will be studied further in the years ahead as part of the Wageningen Solar Research Programme, a programme in which WUR researches the sustainable construction of solar parks, the quality of the landscape and the coexistence of solar parks and food production (agrivoltaics).

The report can be downloaded for free at https://doi.org/10.18174/541057.

Solar parks and biodiversity: room for improvement