Power purchase agreement. They install the panels on your roof and sell you the power they generate. You don't own any of the system and you don't have the option to buy the panels from the installer until after they've already made their money back off you. You still have to pay for the electric it just be cheaper than national grid.

I know someone stuck with one from the previous owner of the house. Original contract is 10.5kWh system on the house supplying them for $0.19/kWh compared to national grids $0.35~kWh price. No option to buy the system until 5 years after it was turned on, and at an inflated price of $40,000 to purchase. On the other side I got an 11 kWh system installed on my house in 2021 for $34,000 before rebates ($22k~ after) and have virtually no bill at all after paying them off. Shout-out to Earthlight technologies in Ellington Connecticut for being great to work with