When large collections of photovoltaic panels are erected as solar farms on undeveloped land, they can harm underlying ecosystems. As an alternative, large parking lots make use of land that is already cleared and produce electricity close to where it’s needed. Plus, they can also shade the cars. A solar parking facility at Rutgers University, in Piscataway, New Jersey, boasts an output of eight megawatts of electricity. If Walmart converted all 3,571 of its U.S. super center lots, the total capacity would be 11.1 gigawatts of solar power, roughly equivalent to a dozen, large, coal-fired power plants.

Most solar installation presently occupy croplands, arid lands and grasslands, not rooftops or parking lots, according to a global inventory published in Nature. Building alternative power sources quickly is important to replace fossil fuels and avert catastrophic climate change, and the process is cheaper and easier to manage by building on undeveloped land than on rooftops or in parking lots. Ironically, putting solar facilities on undeveloped land is often not much better than building subdivisions there. Rebecca Hernandez, an ecologist at the University of California at Davis, notes that developers tend to bulldoze sites, removing all of the above-ground vegetation. That’s bad for insects and the birds that feed on them. The trend to cluster solar facilities in buffer zones around protected areas can confuse birds and other wildlife and complicate migratory corridors.