Ground-mounted solar PV: impact and opportunity
There has been an ongoing debate about the ecological impact of ground-mounted solar photovoltaic panels for a number of years now. Specifically, to what extent is biodiversity affected by their installation on the ground, as opposed to on roofs? Is a combination of a green roof system and roof-mounted panels more effective and better for the surrounding environment? Are they comparable systems?
Before we address those questions, some opening remarks: the power sector is responsible for 25% of greenhouse gas emissions. In that context, solar PV is an important way in which countries can meet the goals of the Paris Agreement and move away from coal and towards clean power. Indeed, at the recently held COP26, 23 new countries committed to phasing out coal power. Solar and wind power are now cheaper than coal in most countries, giving us cleaner air and, indeed, generating more jobs. This is the principal opportunity it presents.
Solar is now the cheapest form of electricity generation in history, according to the International Energy Agency. Indeed, the IEA’s World Energy Outlook 2020 states that there will be
“43% more solar output by 2040 than it expected in 2018, partly due to detailed new analysis showing that solar power is 20-50% cheaper than thought.”
But back to the potential impact. Obviously, land where solar PVs are installed may have value to wildlife. According to a 2019 literature review of research in the field, the main areas of concern pertain to “aquatic invertebrates, birds, bats and effects on local biodiversity”. Let’s look at these in turn in a little more detail.
In terms of aquatic invertebrates, there is some evidence that solar PVs are attractive to them, specifically due to the horizontally polarised light they reflect. The insects take a sensory cue from light when deciding where to lay eggs, so artificial versions of polarised light might encourage egg laying in areas with greatly reduced chances of survival. This suggests that solar farms should be situated away from aquatic invertebrate populations.
With birds, the issue is mirrored light and the possibility of singed wings and collision. There are reports of water birds confusing large groups of solar PVs with bodies of water. There are also potential issues with habitat loss, avoidance, displacement and increased risk of predation.
For context, it should be stated that avian mortality from solar PVs is considerably less than from road mortality and building collisions. It must also be stated that the research has not been undertaken in the UK and tends to have come from desert or savannah environments, so it is not clear what effect solar PVs are having on UK birds, though it is safe to assume that some of the factors discussed here may be of relevance.
In terms of bats, there is a potential risk of collision due to confusing facilities with water, but there’s been no research that directly addresses the effect of solar PVs on bats, and some evidence that while they confuse surfaces for water, they don’t fly into them so are not at risk of harm.
Marstal district, Denmark. Photo: Eric Christensen/Flickr/cropped from original/licensed under CC BY-SA 2.0
Lastly, what about biodiversity? As recently as 2017, the lack of scientific evidence relating to the impact on biodiversity was described as concerning in the research. There is the possibility of a negative impact regarding direct mortality, habitat loss and fragmentation, qualitative habitat alteration, species assemblage changes, microclimate disturbance and pollution. It has been found that solar PV arrays caused seasonal and diurnal variations in soil and air microclimate. There was cooling and drying under the PV arrays and species diversity and plant biomass was lower as well.
However, good management can offset these issues. Recommended approaches include the following:
Installation or retention of boundary features
Planting pollen and nectar strips
Security fencing
Using a grassland habitat
Controlled sheep grazing between panels
Installation of nest boxes, log piles and hibernacula
Indeed, more recent research undertaken in Germany suggests that ground-mounted solar PVs promote biodiversity:
“The scientists claim the installation of ground-mounted plants on derelict land could even raise biodiversity. Open-space PV plants can shelter particular ecological communities. For example, in solar projects in Brandenburg 25 species of grasshopper were found. Solar parks are also particularly suitable as summer habitats for amphibians and reptiles including lizards and frogs. Several bird species were also found in solar fields.”
This is achieved by recreating pre-industrial soil conditions, which encourages the settlement of rare species. Moreover, increasing solar generation capacity – as is required to reduce carbon and fight climate change – requires considerably less land than wind power, so it makes sense in particular for countries with large populations that are land-scarce.
And what of a combination of green roof and solar PVs? It is the case that there are fewer immediate issues and, indeed, obvious benefits, as alluded to here:
“PV panels…increase the diversity of green roofs by providing different niches for organisms to live. Many plants and animals, especially insects, prefer shaded areas and therefore cannot normally survive on living roofs. By adding these areas of shade [the solar PVs], the number of species that will habituate the roof increases. This increases the species richness, and therefore the bio-diversity of the roof system.”
Before we start arguing that it’s an open and shut case, there are differences in scale that need to be mentioned. Generally speaking, ground-mounted solar PV arrays will be significantly larger than roof-mounted PVs. Ground-mounted options are dearer, too. Both are options for individuals wishing to get green energy for their home, but only ground-mounted is an option for larger solar parks. There is, therefore, an element of apples and oranges about this comparison.
Also, to some extent, green roof and solar panels compete with each other. And, despite what was said about shade above, another review of the literature suggests that increasing that is a problem, as ‘direct shade throughout the say is not beneficial to most species”, though it does encourage new species. Shade also leads to less heat storage.
What is clear is that for the consumer, “when you combine [green roof and solar PV] together, both perform better. It’s a symbiotic win-win”. From the point of view, on the other hand, of large-scale attempts to replace electricity generation with solar and the attendant fighting of climate change, ground-mounted is still the go-to approach. As more studies in bespoke environment are undertaken, we will get a better idea of the specific negative impact in particular environments.