France now requires any existing parking lot bigger than 1,500 square meters to cover half its surface with solar canopies or shade trees, and the largest lots were due in July. One supermarket chain is roofing car parks at 350 of its stores, covering nearly 180,000 spaces where shoppers used to park in the sun.

A big supermarket car park on a hot afternoon: rows of cars on black asphalt, windshields glaring, interiors turning into ovens, the whole surface soaking up heat and giving nothing back.

Now picture the same lot with a roof over it, solar panels on steel frames, cars in the shade, a meter ticking over as the panels feed power into the grid.

France has passed a law meant to move a lot of its parking from the first picture to the second, and the first big deadline has just passed.

The interesting part isn’t only the panels. It’s the land. A parking lot is ground that’s already been cleared, paved, and connected to roads and power, and for most of the day it does very little except bake in the sun. That’s what makes the French rule worth watching, and also what makes the choice it forces, panels or trees, more interesting than the headline suggests.

What the rule actually says

The cutoff is 1,500 square meters. Above that, outdoor car parks, both new and existing, have to cover at least half their surface. The requirement comes from Decree No. 2024-1023, which puts France’s renewable-energy law into effect, and the deadlines depend on size. Lots larger than 10,000 square meters had to comply by July 1, 2026. Lots between 1,500 and 10,000 square meters have until July 1, 2028. Owners who miss the deadline face fines of up to €40,000 a year until they fix it.

The shape of it is clear: cover half of a specific kind of already-paved space, phased in by lot size, with money on the line for ignoring it. 

The nuance the headline flattens

When the mandate first landed, it read like a solar-carport rule. Cover half the lot, put panels overhead, done.

Then in May 2025 the National Assembly softened it. A change from parliament let owners hit the 50% target with solar canopies, shade trees, or a mix of the two. The amendment frames it as “a common-sense measure, which does not call into question the ambition of the law.”

The renewables industry read it very differently. The trade group SER argued that “there is no longer any formal obligation to solarize these parking lots, since simply planting trees will be sufficient to comply with the law.” That’s an advocacy read from a group that would benefit from more panels, not a neutral summary, and the amendment’s backers would say a shaded, cooler lot is a real win either way. But it does capture the tension the softened rule creates. Half the surface has to be covered. Whether that half generates electricity or just casts shade is now, in many cases, up to the owner.

What one chain doing this at scale looks like

Carrefour is the clearest case of a company treating the mandate as a reason to build rather than a compliance headache. Ahead of the rules taking full effect, the supermarket group signed a 20-year deal with solar developer GreenYellow to fit solar carports across its stores. GreenYellow will install them on the parking lots of 90 hypermarkets and 260 supermarkets, covering almost 180,000 parking spaces.

The output figure is what gives the project its scale. The canopies are expected to produce around 450 GWh a year, which GreenYellow compares to the electricity use of a city of 200,000 people. Carrefour hopes to cover 20 percent of its stores’ electricity needs from the project within three years. The rollout is staged, with GreenYellow planning to finish half the program by the end of 2026 and the first sites connecting in 2025. This is what the panel version of the law looks like when a single owner commits to it across a whole country.

Two ways to read the payoff

There’s a genuine case for the solar reading, and it’s mostly about land. Parking-lot canopies use ground that’s already sealed and sit close to the shops, offices, and chargers that need the power.

A Yale Environment 360 piece by Richard Conniff puts the appeal plainly, arguing that canopies offer “a host of advantages” by using land that is already cleared, producing electricity close to those who need it, and shading cars too. The same piece notes how little of this is happening yet: just 2.5 percent of US solar power comes from urban areas, while most sits on farmland and deserts. The space adds up, too. Conniff notes that a single five-acre Walmart parking lot could support a three-megawatt solar array if you roofed it, precisely because the panels go over space that was already paved.

The tree reading is simpler and older: shade. Hot asphalt is a big reason cities run warmer than the countryside around them, an effect the EPA links to lost shade and paved ground. Both canopies and trees fight that, and the cooling is real. The EPA estimates that shaded surfaces can run 20 to 45°F (11 to 25°C) cooler than unshaded ones at their hottest. Trees are cheaper, pleasant to walk under, and they cool a lot down. What they don’t do is generate a single kilowatt-hour.

That’s the trade the softened rule leaves open. A lot roofed in panels produces power and shade. A lot planted with trees produces shade and a much smaller bill, but no electricity, which is exactly why the solar industry pushed back. Neither option is wrong for every site. The premise underneath both is the more interesting question: the surface was already there, already sealed, already doing nothing for most of the day. France has decided that half of it, at minimum, should start earning its keep, and left the harder argument about how, panels or leaves, to be settled one car park at a time.