Expanding solar generation means expanding solar generation’s footprint. While some reservoirs and lakes can accommodate floating solar, most solar developments happen on greenfield sites, often on arable land.
On the average solar farm, developers replant these green fields with grass. This seems like an obvious solution: grass seed is cheap and easy to maintain, requiring only an occasional mow. The plant holds the ground together and eases drainage, making the panels themselves more accessible and stable. From a human perspective, a field of grass looks better than a field of mud.
But is this the best solution? In recent years, some solar farms have claimed to be “pollinator-friendly”, based on their planting after construction. These aim to encourage pollinating insects, such as bees, which face rapidly declining numbers. Can these projects benefit insects, solar developers and biodiversity on the whole?
What makes a solar farm “pollinator-friendly”?
Pollinator-friendly solar farms involve planting native shrubs, grasses and flowers beneath solar panels. Generally, the selection and planting of these involve developers working with local conservation charities.
Press releases for pollinator-friendly spaces often include idyllic pictures of sunny wildflower meadows. While these are attractive, they are not always possible and can miss the point of planting more naturally.
Paul Hetherington, a spokesperson for UK insect conservation charity Buglife, told us: “I think the first and most important issue though is what was the site before it became a solar farm. Clearly, a vibrant meadow should not be destroyed to create a solar farm that then claims to be pollinator-friendly.
“In terms of planting, good planting would see a wide variety of wildflower-rich grassland created under the panels with an emphasis on looking for year-round flowering and a good variety of pollen and nectar sources.
“Another big way a solar farm can be pollinator-friendly is in edging with flowering native hedging. In the UK, this could be something such as blackthorn and hawthorn. In the ideal environment, there should also be areas of bare earth for ground-nesting bees. A south-facing bank would be ideal, as would a source of water.”
For many, the word “pollinator” inspires them to think of fuzzy bumblebees, hives, and honey. However, Hetherington warns: “Placing honeybee hives on site would not be pollinator-friendly as the honeybees would likely require more food than the site could provide. This would put them in direct competition with native pollinators.”
Who currently makes pollinator-friendly solar farms?
Growing diverse plants for insects can have other benefits.
In Australia, water company SA Water replanted native bushes and grasses around its solar panels, which power its pumping stations. The 500,000 solar panels lay on former farmland with limited cover from perennial plants. In summer, this would lead to weed invasions and dust issues.
As a result, the company worked with local conservation group Succession Ecology to plant one tonne of seed across its sites in South Australia. The group’s director and revegetation consultant Glenn Christie said: “The beauty of the seed varieties collected is its ability to create a native biodiversity attracting insects and birds with the vegetation only reaching knee height as to not impact solar performance.”
In the US, Engie Distributed Renewables says it considers planting “as a standard element” of its projects. It continues: “Each site is seeded with a diverse mix of nearly 25 different plant species, including plants native to the region.” The company’s projects in Nebraska and Wisconsin are far from the largest projects around, but give pollinators a space amongst arable land.
Also in the US, Lightsource BP consulted with “ecology experts” and universities to plant its solar farms with pollinator habitats. The biodiversity appeal helped attract telecoms giant Verizon into a power purchase agreement for a project in Indiana.
The company has also started construction on the Wildflower Solar project in California, where it would use 1.25 acres of the 91-acre site to develop a wildflower meadow. Utilities in California have encouraged schemes like these, with some renewable electricity providers requiring solar farms on arable land to make themselves pollinator-friendly.
At least seven states in the US have laws encouraging the adoption of pollinator-friendly practices. Other states have programmes to encourage pollinators, and databases of local plants to help developers make their own decisions. While some authorities and developers score developments’ approach to pollinators on several factors, there is no single widespread system of verification. As a result, the words “pollinator-friendly” can mean very different things, or very little at all.
Is pollinator-friendly solar generation just “greenwashing”?
Making solar farms pollinator-friendly certainly provides a better image to planners and communities considering a development. But across power generation, environmental initiatives have a reputation of “greenwashing”, where companies take part in programs to improve their public relations, without significantly benefitting the environment.
In the case of pollinator-friendly solar generation, studies have suggested that improving pollinator habitats leads to a small improvement in energy output. This comes from better solar panel efficiency, as good planting gives a cooler microclimate. Operations and maintenance costs from mowing grass are also reduced with pollinator-friendly plants. On arable land, pollinator-friendly planting also improves nearby crop yields and water drainage, as plants grow stronger with a healthier ecosystem around them.
Because insects do not respect land boundaries, measuring the impact of pollinator planting can have difficulties. Most studies look at the benefits of agriculture over power generation, but those benefits could compel farmers and landowners to seek out solar developers. A 2018 US Department of Energy study found: “If all existing and planned solar facilities near soybean, almond and cranberry crops included pollinator habitat and increased yield by just one per cent, crop values could rise $1.75 million, $4 million and $233,000 respectively.”
What else can grow beneath solar panels?
This link between photovoltaic solar and agriculture can all go one step further.
German developer BayWa RE has a division devoted to what grows beneath solar panels. However, their approach involves planting productive crops beneath solar panels, blending agriculture and power generation.
The company calls this Agri-PV and tells us it has a levelised cost of electricity of $10.8/kWh (€9/kWh). This stands at a similar cost level to small-scale rooftop photovoltaics, notably more costly than commercial-scale photovoltaic generation. However, these systems produce more than just energy.
Solar modules can benefit the yields of several crops. In the hot and dry summer of 2018, the panels led to higher yields of celery, winter wheat and potatoes. The company has started tests on berry crops, tea and herbs, believing they have significant potential when combined with solar.
BayWa RE has developed projects which most solar developers would consider small. However, head of Agri-PV Stephan Schindele told Power Technology that these systems can scale up as easily as conventional solar if they get the support of landowners.
Farmers save on costs for foils, plant protection, irrigation and herbicides. Schindele continues: “We see further cost reduction opportunities, if the technology pushes from pilot projects come together with demand pulls, from subsidies for market introduction. Good examples of Agri-PV implementation can be found in Japan, South Korea, France, and Massachusetts, US.”
However, he warns that this can have drawbacks for power generation: “As the photovoltaic array must follow the lines of the plant stripes, rows or machine paths, a strict south orientation is rarely reached.
“Also, because of the site’s usage, the required distances between rows, shadowing effects, table sizes and the use of DC cabling we cannot optimise generation to its best, as the agricultural production prevails. This is necessarily a compromise in efficiency and hence levelised cost of energy. However, having an agricultural business ongoing under the panels does obviously save on maintenance costs, as grass cutting, fencing and video surveillance are obsolete.”