Making space for power: how much land must renewables use? 

In temperate countries, the energy transition will mean some arable land must go toward power generation. Already, growing populations have put pressure on agriculture and farmers face increasing demand to produce more with fewer chemicals. While farming and wind power can work together, solar farms threaten to indirectly reduce crop yields.

A recent study in the PLOS One journal ‘Supply-side options to reduce land requirements of fully renewable electricity in Europe’, examined where generation might go in order to minimise its use of land. It found that generating Europe’s electricity using only onshore wind and solar would require approximately 2% of the continent’s land, equivalent to an area larger than Hungary. Worldwide, a fully renewable future could mean solar alone occupies a land area larger than the UK.

Some will see offshore wind as an obvious solution. Fixed-bottom wind turbines have opened shallow waters to offshore power, greatly benefiting countries such as the UK and the Netherlands. The study says this could reduce land requirements by 50%. It would, however, come with a 5% cost penalty that could deter developers when there are cheaper options on land.

In the near future, floating wind solutions seem set to open up more waters for offshore wind. The first medium-scale projects have now begun operations, and planners are looking at large-scale developments.

However, this answer does not help regions with little or no coastline. For countries such as Switzerland, the energy transition’s opportunity for energy independence is threatened by the need for land. The country currently imports 85% of its power, and it aims to phase out its own nuclear generation by 2034. Because of this, the expansion of its renewables sector will rely on making use of its relatively small area.

Meanwhile, renewable development in sub-Saharan Africa already faces problems from rudimentary transport systems. Asking farmers to risk their arable land on complex technologies unproven to them could be a hard sell.

In Europe and North America, farmers can generally work around onshore wind turbines. As the Canadian Wind Energy Association put it: “Generally, each tower base is about eight to 10 metres across, and spaced from 250 to 800 or more metres apart. Together, an entire wind farm, including towers, substation, and access roads, uses only about 5% of its allotted land.”

But any renewable developer will know a turbine’s footprint extends beyond its fields. Communities often oppose local developments, and other studies have found varying evidence of the effect turbines have on nearby property values.

However, land use may not be as simple as deciding between crops and power. ‘Agrivoltaic’ projects have aimed to find a balance between farming and energy generation that benefits landowners.

Researchers at the University of Cambridge recently developed tinted solar panels that would allow plants to grow beneath them. The panels absorb more than half of the light hitting them, while allowing the colours needed by plants to pass through.

In a greenhouse setting, the researchers grew high-value basil and low-value spinach, testing their yields. Both plants grew smaller, but in different ways.

Lead researcher Dr Paolo Bombelli said: “For high value crops like basil, the value of the electricity generated just compensates for the loss in biomass production caused by the tinted solar panels. But when the value of the crop was lower, like spinach, there was a significant financial advantage to this novel agrivoltaic technique.”

In an effort to absorb the lower levels of light, the spinach put its resources into growing larger leaves than regular plants. This meant that the combined value of the spinach and power produced increased the monetary yield of the site by 35%. While this sounds promising, the researchers warn it would not work for all plants: the total value from the basil plot increased by only 2.5%.

Similarly, four projects in the Netherlands aim to grow different berries beneath solar panels. German agriculture company BayWa developed the project and has now started developing pilots for apple and pear crops.

BayWa AgriPV product manager Stephan Schindele said in a statement: “Following the success of our pilot project last year, we have now expanded the project to increase its size to 2.7MW. This latest extension involves the installation of 10,250 solar panels across 3.2 hectares of raspberry crops, generating enough clean energy to power close to 1,250 households.

“Careful monitoring throughout the pilot study showed that the climate under the panels is in fact more stable than under traditional plastic arches. The panels created a more favourable lower temperature and better protected the crops from the weather.”

The Cambridge project was developed with local solar company Polysolar Domestic. This company specialises in solar generation within glass panes, made to fit into household design. In turn, this also offers a less-intrusive way to install photovoltaic panels in a domestic setting.

Still, a 2018 paper by the US National Renewable Energy Laboratory expects 63% of the country’s 2030 solar generation to come from ground-based panels. As such, the solution may lie in changing how we think of the land beneath utility-scale solar.

Traditionally, developers remove existing plants, grade the soil, and compact the surface after installation. This destroys any existing ecosystem and inhibits the development of a new one. Conversely, several projects have looked to use solar farms as a space for biodiversity, making them more appealing to planners and communities.

Optimising land use can be as simple as maximising efficiency. Some solar plants have looked to nature to arrange their panels in the most efficient formation possible. Even in fertile areas, there may be enough brownfield sites to generate sufficient power. In California, one study suggested that the state could generate 13 times its power demand using only photovoltaic generation on contaminated or developed land, and unused reservoirs.