Community solar needs space to grow. Warehouse rooftops have lots of it.

Community solar lets utilities sell power from a shared solar array to nearby customers, who get a discount on their electric bill without installing anything on their own roof. Developers are now looking at warehouse rooftops as prime real estate for these projects, since most warehouses use only 30 to 40 percent of their roof space for their own power needs. In Oakland, California, logistics company Prologis and public energy provider Ava Community Energy just switched on a 720-kilowatt rooftop array that will supply power to income-qualified subscribers with a guaranteed 20 percent cut to their monthly bill. Prologis has similar projects underway in New Jersey and Illinois.

Whether this matters to you depends heavily on where you live. Community solar programs currently exist in about half of U.S. states plus Washington, D.C., including Colorado, Illinois, Maryland, Massachusetts, New Jersey and New York. Some of these states, like New Jersey, are expanding their programs and prioritizing rooftops over open land. California, by contrast, has tight cxaps on how much community solar can be built, and regulators there have recently blocked efforts to expand it, arguing it costs more than large solar farms built on open land.

If your state has a community solar program, it's worth checking whether a provider in your area offers a subscription — these arrangements are pitched especially at renters and lower-income households who can't put solar on their own roof, offering bill savings without any equipment or installation on your property.