Contracts to sell electricity directly to corporate users are among the key demand drivers for wind and solar power, while the influence of state mandates wanes, according to a report by Moody’s Investors Service.

Multiple factors are spurring corporate power deals, especially from companies that have set their own sustainability goals. And the shift comes as costs continue to fall. Power purchase agreements (PPAs) with wind farms are now available for as low as $15/MWh, according to Moody’s, and $35/MWh for solar.

“The economics are making it easier for new entrants to join,” says Lesley Ritter, an analyst at Moody’s. Community choice aggregators are another new entrant, formed by counties or cities to encourage more clean power.

Corporations agreed to buy nearly 3.7 GW of power generated by clean-energy projects in 2015 and another 2.5 GW last year, almost all from wind and solar, according to Bloomberg New Energy Finance (BNEF). By early March, corporations had bought 340 MW this year.

Technology companies led by Alphabet Inc’s Google are among the biggest buyers of clean power. Companies are signing PPAs, in part, for long-term visibility into their electrical costs. Some, like Google, are also keen to add more green electricity to grids. There have been at least 32 corporate buyers to date, Moody’s found.

“There are a ton of companies besides Google and Amazon that still have tremendous power needs and are possible targets for developers,” says Kyle Harrison, a New York-based analyst at BNEF. “There’s still an addressable market for developers. It hasn’t been exhausted.”

The emergence of corporate buyers comes as states are meeting their clean-energy targets, renewable portfolio standards, or RPS.

“The drivers are no longer RPS,” says Swami Venkataraman, a Moody’s analyst in New York. “RPS procurement has pretty much ground to a halt.”

Moody’s expects some states, including California and New York, will eventually increase their RPS targets. Declining federal wind and solar subsidies may also motivate utilities to buy more clean energy.

“In 2018, you’ll see a big procurement boom from both utilities and corporate customers,” says Craig Cornelius, senior VP of renewables at NRG Energy. “Developers will be telling those customers: ‘If we can’t commence in 2019, we won’t be able to get the full value of the subsidies.’” That means dependence on corporate buyers may not last long. “They probably won’t be the only show in town,” Cornelius says.