This story is reproduced here as part of the Climate Desk collaboration.

Rooftop solar power systems cost a lot less these days than they did five or 10 years ago, and with many solar companies now offering leases and loans, it’s safe to say that going solar is more affordable than ever before. That trend goes a long way to explaining why solar, while still making up less than 1 percent of the total U.S. energy mix, is the fastest-growing power source in the country.

But access to solar power is still overwhelmingly skewed toward affluent households. Of the roughly 645,000 homes and business with rooftop solar panels in the U.S., less than 5 percent are households earning less than $40,000, according to a report earlier this year from the George Washington University Solar Institute. The typical solar home is 34 percent larger than the typical non-solar home, according to energy software provider Opower.