We’ve all seen arrays of solar panels on rooftops. They convert the sun’s energy into electricity, lowering the homeowner’s electric bill—and maybe even adding power to the grid. On a small scale, they can maintain the efficacy of vaccines in remote locations. On a larger scale, utilities install massive solar arrays as part of their decarbonization strategy.
But as we install more solar arrays, it’s worth thinking about how to make the most of them. That is, how can we make solar panels work more efficiently? And what else can we get them to do for us?
Swimming pools and green lawns notwithstanding, California is a desert, and demand for its scarce water increases as the population grows. Meanwhile, climate change has brought hotter, drier summers.
The apparent ease of California life is an illusion, and those who believe the illusion real live here in only the most temporary way. I know as well as the next person that there is considerable transcendent value in a river running wild and undammed, a river running free over granite, but I have also lived beneath such a river when it was running in flood, and gone without showers when it was running dry.—Joan Didion
California’s 6000 km (3700 miles) of aqueducts supply water to the cities and fields. In transporting the water, they lose a great deal of it to evaporation. Scientists at the University of California propose to float solar panels on reservoirs and irrigation canals. This has the dual benefit of reducing evaporation and cooling the solar panels so they work more efficiently.
Covering the canals with solar panels would prevent evaporation of roughly 40,000 cubic metres of water—16 Olympic swimming pools’ worth—from each kilometre of canal every year.—Nature Sustainability
Moving all that water takes a lot of electricity to power the pumps. Indeed, California’s water conveyance system is its largest consumer of electric power. Solar panels could make the system largely self-powering.
It is easy to forget that the only natural force over which we have any control out here is water, and that only recently. In my memory California summers were characterized by the coughing in the pipes that meant the well was dry, and California winters by all-night watches on the rivers about to crest, by sandbagging, by dynamite on the levees and flooding on the first floor.—Joan Didion
You might think that generating electricity from a solar farm would be a good use of land. But what if you could make the solar panels more efficient while also providing a habitat for pollinators? That’s the idea behind a suite of Minnesota statutes that regulate solar installations.
An owner of a ground-mounted solar site with a generating capacity of more than 40 kilowatts may follow site management practices that (1) provide native perennial vegetation and foraging habitat beneficial to game birds, songbirds, and pollinators, and (2) reduce storm water runoff and erosion at the solar generation site.—Minnesota Statute 216B.1642
For example, a Chisago County solar farm owned by Enel Green Power uses an assortment of native plants to provide a habitat for bees and other pollinators. The vegetation makes for a cooler environment for the solar panels, so they operate more efficiently. The perennials’ long roots improve the soil. To manage the plants, a herd of sheep grazes on the land, controlling dead material and stimulating new growth to reduce the danger of fires. A miniature donkey comes in occasionally to protect the sheep from coyotes.
Video: “Sheep may safely graze” by J.S. Bach, extols the benefits of good government. However, it does not mention pollinators or donkeys.
At about $300 to $350 per year per acre, hiring sheep to maintain the vegetation costs less than other methods. For the sheep farmers, that means they get paid rather than having to pay for grazing rights.
Researchers around the United States are investigating collocation of solar panels and crops. Despite what you might expect, it isn’t necessary to choose solar panels over crops. If the solar panels are high enough off the ground, crops can grow underneath. In hot climates, the shade from the solar panels may even be beneficial.
“Agrivoltaics,” or growing produce beneath panels, is especially promising in hot, arid regions, say experts who have planted cherry tomatoes and peppers beneath them at the University of Arizona’s Biosphere 2 laboratory. Those crops usually match or exceed ones in a traditional environment, according to the team’s findings. With less direct sunlight, they lose less water to evaporation, reducing irrigation demand.—John Flesher and Tammy Webber, Star Tribune, 4 November 2021
While the presence of solar panels may preclude the use of large agricultural equipment, the majority of these farms are small. They can have difficulty breaking even. But leasing land for solar panels while still using it to grow crops can make them economically viable.
As the country increases its supply of renewable electricity, up to 10 million acres could become solar sites by 2050. Agrovoltaics could mitigate the loss of farmland that this conversion would otherwise entail.
Solar panels take up a lot of space, which big-box stores have in abundance on their roofs. A report from the Environment American Research and Policy Center estimates that superstores in the continental United States have about 7.2 billion square feet of roof area. About two-thirds of that space is suitable for solar panels. If big-box stores were to take full advantage of that space, they could produce about half of the electricity they need—and reduce annual CO2 emissions by 52 million tonnes.
Walmart, with 784 million square feet of roof space, has the greatest potential for solar power. However, Ikea already has solar panels on 90% of its US stores. And Target has solar panels on about a quarter of its US stores, where they generate 15 to 40% of the stores’ electricity needs.
There’s even more potential for solar power if the stores installed them in their parking lots as well. The panels could provide a canopy over them, sheltering cars from the hot sun. The Ikea store in Baltimore has already done this.
Although it may seem like an oxymoron, solar panels can power refrigerators. That’s a practical solution for portable refrigerators to transport vaccines in Africa. The vaccines stay consistently cold so they remain effective, and they don’t have to depend on power from an electrical grid.
Another possibility for low-energy cooling is passive radiative cooling.