But it’s hard to think of a better urban area to use than a parking lot. Besides being unpleasant on the eyes, they are usually quite large, which means they have enormous energy-generating potential.
Just installing solar panels in the parking lots of 3,751 Walmart supercenters across the U.S. could generate the same amount of electricity as about a dozen coal-fired power plants, according to a 2021 study Pierce co-authored. (Even if you factor in the part-time nature of solar energy, Pearce thinks that if you covered those Wal-Mart lots, you could permanently close two, maybe even three, of these plants in sunny areas.) In France, the government reckons solar canopies could generate up to 11 gigabytes of electricity. watts of renewable energy, or the equivalent of 10 nuclear reactors. This accounts for approximately 8% of the country’s total electricity output.
Installing a solar canopy also helps drivers. They would provide shade on sunny, warm days, potentially reducing the need for air conditioning when people hop into their cars, and in winter they would provide shelter from rain and snow. If the vehicles parked below them are electric, the energy generated can also be fed directly to those cars. Currently, most commuters charge their EVs at home outside normal working hours. Free charging while shopping or working allows them to bypass peak prices.
Connecting a parked electric car to a photovoltaic canopy could even help balance the grid. Because traditional grids have no energy storage capacity, the electricity coming in must match what’s being consumed—and having too much electricity on the grid is a problem. For solar, especially during peak sunshine periods, this could mean production has to be halted. But if you can store excess energy in EV batteries on site, you can maximize the potential of solar power during peak generation times.
“During the day, they can store energy,” Nathanson said of the parked electric car. “During peak electricity usage, around early evening, they can feed power back into the grid.” Bringing so many individual devices to the grid—and making sure no one ends up short of energy—requires a lot of smart automation. It also requires two-way charging devices, which are not widely available yet. But the potential to harness solar power to get smarter is there.
Not every parking lot can be converted into a power plant, though. Some may have too much shadow, perhaps due to tall buildings nearby. In countries in the northern part of the world, where the sun is lower on the horizon, long shadows will be a bigger problem, especially in winter. In other locations, the panels could reflect sunlight onto nearby buildings or worse, roads, warns Dylan Ryan, lecturer in mechanical and energy engineering at Edinburgh Napier University in Scotland. “Are we going to cast sunlight into the eyes of the people working across the street?”
The biggest issue, though, is cost: installing solar panels above a parking space is several times more expensive than installing them on the ground or on a roof due to the need to build support structures. (These costs may be greater in the UK than in southern Europe, for example, where car parks do not yet have sunshades.) One of the lingering questions in the French proposal is how car park operators will pay for these installations. Without the subsidy, it’s hard to imagine too many operators installing optional solar roofs because of the investment required, Pearce said.
Of course, parking lot operators can recoup their upfront investment by charging customers for EV charging, or they can use the electricity themselves in whatever business the parking lot serves. Or electricity can be sold back to the grid. “Whether you’re just selling electricity to the grid or just using it in your business, you’ll pay less for electricity,” Pearce said.
That’s not to say that solar farms are only for urban areas. But there’s a clear benefit to generating more solar energy closer to where people are — and there’s clearly a need to find a way to do it that doesn’t get tripped up by NIMBYism. Using parking lots for solar farms could solve this problem, and for these reasons, the French legislation is a big, albeit radical, step in the right direction. “You’re taking advantage of essentially free real estate,” Ryan said.
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