PNAS reports on some unanticipated consequences of solar farming – but things that banks of solar panels that are unexpectedly good, not bad:
To generate as much energy as a conventional 1-gigawatt power station, an array of solar photovoltaic (PV) panels needs to cover about 80 square kilometers of land. Unsurprisingly, solar development faces increasingly organized resistance from many rural communities and activist groups, who see it as an enemy of farming.
In 1982, researchers at the Fraunhofer Institute for Solar Energy (ISE) in Germany proposed a stunningly simple solution: set solar panels a few meters above the ground, and grow food underneath. Their original sketch shows angled panels with fairly large gaps in between, so the crops still get plenty of sunlight (1). This concept began to bear fruit in the early 2010s, with field trials in Japan and Europe. Japan now has about 3,000 farms with small solar installations set up on stilts, which are financially supported by government funding and known as solar sharing. In the United States and Europe, this idea is usually called agrivoltaics (AV), and it comes in a mouth-watering array of varieties.
The simplest approach is to plant grass under the panels and unleash some sheep. The United States already has more than 15,000 acres of solar grazing, including a huge 4,700-acre site at Topaz Solar Farm in California. The sheep gain shelter from the panels, and it saves on the cost of cutting the grass. With an eye on improving biodiversity, other projects plant native vegetation beneath their panels to support pollinating insects. This can also restore soils that have been depleted and compacted by decades of intensive farming, locking up carbon from the atmosphere. Both of these are low-maintenance options, and they work with panels set less than 1 meter above the ground, which keeps installation costs down.
In 2016, for example, [plant ecologist Greg] Barron-Gafford’s team started an AV project growing cherry tomatoes, chiltepin peppers, and jalapeños—“things to make salsa, because if all else fails, you can still eat the science,” he says. The researchers found that the panels kept plants cooler during the day and warmer at night, and they held more moisture in the air. These less-stressed plants produced just as many jalapeños, twice the crop of tomatoes, and three times the amount of chiltepin peppers as those on a control plot (2). They also needed substantially less watering, a key benefit in a time of worsening water shortages around the world. Water evaporation from the plants even helped to cool the panels and increase electricity output.
AV must also be tailored to local climate, landscape, and soil—for example, by spacing panels more widely in darker latitudes to let in more light. To fine-tune these designs, Alexis Pascaris at the Michigan company AgriSolar Consulting is working with Colorado developers Sandbox Solar to create a software tool called SPADE, which will calculate light c
onditions for a given location and panel configuration and then identify crops that could thrive there.
Although AV generally offers higher crop yields in sunny, water-stressed areas, it can reduce yields in damper, darker climes. Even so, AV can put less pressure on land than separate farm and solar installations. For example, if a hectare of AV in Germany produces as much food as 0.8 hectares of conventional farming, and as much power as 0.7 hectares of conventional solar, it still saves half a hectare of land.
[via Tim Kellogg on Mastodon]