Solar plants keep getting bigger: The new Topaz Solar Farm, in a remote part of southern California, sprawls over an area about a third of the size of Manhattan. In February, another solar farm of roughly the same size–with 9 million solar panels–opened in the Mojave Desert. Later this year, an even larger project will open in Antelope Valley.

Together, the three new projects will provide enough power for over half a million homes. But there’s a downside: They’re all in former open spaces that once provided habitat for wildlife, and because they’re in remote areas, some of the energy they produce gets lost along the way to consumers. A new study in Nature Climate Change says that plants like these actually aren’t necessary: We can get more than enough solar power by building in cities instead.

The study looks at California, because the state is aggressively increasing renewable energy, and finds that by using land that’s already developed, like rooftops and parking lots, solar power could provide the state with three to five times as much energy as it uses.

“I questioned whether we have a constraint on land,” says researcher Rebecca Hernandez. “It was striking to me that there seemed to be sort of this mismatch of available places to put solar. I wanted to really understand how much land do we have, how much land is available, all these land dynamics that really were not quantified before, and sort of paint a better picture.”

The study maps out developed areas that are best suited for either photovoltaic panels or concentrated solar power (CSP). California has an area about the size of Massachusetts that is well-suited for PV panels, and an area about the size of Delaware that is a good match for CSP. If these spaces were fully plastered with solar tech, they could provide over 20,000 terawatt-hours of power every year.

By building in and near cities, we could also add new solar power more quickly, because remote plants require new transmission lines. “We have to build out infrastructure to catch up to these places,” Hernandez says. “Really, our solar energy installations are now dictating the infrastructure of our grid, which is sort of backwards.”

Remote solar farms also lose power as it is transmitted over long distances, so it’s not as efficient. “There’s two problems with solar energy,” Hernandez says. “One is that we need to deploy it rapidly, and two we need to do it efficiently. We’re on track to meet our renewable energy goals, but is it fast enough? Many of us would probably argue it’s not, because we’re running behind climate change. The truth is that California’s not being effective.”