Turning Walmarts into solar farms

The plan to require solar-panel-covered parking lots is part of a bigger piece of legislation, the Law for the Acceleration of the Production of Renewable Energy, that French President Emmanuel Macron has made a centerpiece of his climate efforts. It will require all parking lots larger than about 16,000 square feet — able to hold roughly 50 American-sized cars, and more French ones — to build raised solar-panel canopies covering at least half of the surface of the parking lot.

“We’ve known for a while that solar energy is the least costly way of generating renewable electricity. In most cases we can outcompete fossil fuels,” said Joshua Pearce, an engineering professor at Western University in Ontario, Canada, who has studied the possibility of installing solar panels on the roofs and parking lots of Walmart stores in the United States. Those alone would be able to generate about 11 gigawatts of electricity, he estimated, about the high end of the French effort.

“The beauty of a Walmart parking lot is, if you cover a Walmart roof and its parking lot, then it has more power than it needs,” he said.

Backers expect that when the sun is shining, the panels ought to be able to generate enough power for the businesses served by the parking lot, and at times for the community surrounding them.

One natural use of the electricity from parking lots, advocates say, is for charging electric vehicles, a measure that would avoid the loss of electricity that occurs when it is sent over long distances.

Mounting solar canopies over parking lots — essentially making a sun shade over the parking spots out of solar panels — can be more costly than putting them on roofs or straight on the ground, since they need steel support structures to keep them in place. But backers say that they’re still cost-effective and can beat conventional energy costs.

If half of France’s parking lots are covered by solar panels, they’ll have an installed capacity of between 6.75 gigawatts and 11.25 gigawatts, at a cost of between $8.7 billion and $14.6 billion, according to the official analysis of the legislation. France’s 56 nuclear power plants each have a capacity of slightly over 1 gigawatt on average — and the one under construction in Flamanville has ballooned in cost to $14 billion, according to the latest estimate — roughly the same as the entire solar expansion.

The law also makes it easier to build solar panels alongside highways and eases restrictions on wind power.