Residentialsolarfinancier Sunnova is now offering something that looks like a loan but isn't really a loan.

When we spoke with Sunnova CEO John Berger late last year, he was adamant about selling solar as a service and had no plans to offer cash sales or loans, despite some rumors to the contrary.

Firms such as SunPower, SolarCity, Clean Power Finance, Sunrun, NRG, Sungevity, SunEdison, Kilowatt Financial, Sungage, Mosaic and Dividend Solar are already in the solar loan business. Loan specialists Sungage, Mosaic and Dividend Solar raised hundreds of millions of dollars in 2014. Vivint, one of the last holdouts, has expressed a "desire to expand into additional financing products, such as loans," according to an investor note from Credit Suisse.

Sunnova's new program lets customers "pay a fixed amount each month over the 25-year term at a kilowatt-hour price substantially less than what they currently pay for power," while providing a warranty along with O&M. The customer owns the system at the end of the term.

That sounds like a loan.

Sunnova insists that its program "is not a loan product. While a loan is a transaction between the customer and the bank, a retail installment sale...is a transaction between the customer and Sunnova where the customer pays Sunnova in monthly installments."

Sunnova notes that its product "can also be transferred in the event of a sale of the home, making it more flexible and convenient than competing products, such as loans." The non-loan product will launch this quarter in California.

SolarCity did not rush into the loan business, but its loan product sounds a lot like Sunnova's non-loan with a fixed annual percentage rate, SolarCity as the direct lender to its customers, along with a 30-year warranty, production guarantee, and O&M service.

SolarCity CEO Lyndon Rive said that solar loans could be half of the company's new business in 2015.

Third-party ownership remains the dominant model for financing a residential solar installation in the U.S., but that's changing. Direct ownership via loans (and other mechanisms like PACE) is gaining traction, because PV systems continue to get cheaper while financing options continue to improve.