PORTLAND - The Public Utility Commission has given Oregon businesses a bigger incentive to put solar panels on the roofs of their factories, warehouses and offices under new rules that went into effect Friday.

The updated policy increases the size of renewable energy systems eligible for a state program that requires electric utilities to buy electricity when those systems produce more than their owners can use. The action could spur investment in solar energy in the private sector because it allows companies greater leverage over their electricity costs.

“We are going to see a lot larger (solar) systems going in on commercial buildings,” said Lisa Schwartz, a senior policy analyst at the commission. “The nice thing about this is you have the private sector putting up these facilities that will be providing energy and some capacity, and utilities won't have to put in additional resources.”

Oregon has a program known as “net-metering,” started in 2000, that requires utilities to buy excess electricity generated through renewable resources by customers connected to the grid. But the old rules capped the size of energy systems that could apply to the program at 25 kilowatts - a typical size for a home solar system but undersized for most businesses.

On Friday the cap was upped to 2 megawatts. The change could be especially useful for large businesses with the financial wherewithal - and physical space - to invest in solar panels which typically require a large upfront capital investment but takes years to recoup their cost.

“It's a good thing for us because it promotes technology and renewables, giving our customers the flexibility to sell that power back into the system,” said Gail Baker, a spokeswoman for Portland General Electric. “As long as it's safe and reliable for the system, we think it's great.”

Supporters of the expanded program said it would also help utilities meet renewable energy mandates passed by the Oregon legislation earlier this year requiring the state's largest power providers to draw 25 percent of their electricity from renewable sources such as wind, solar and waves by 2025.

“This kind of policy is critical to making solar energy work because it makes it financially viable for the private sector,” said Jeremiah Baumann, a spokesman for Environment Oregon, an environmental advocacy group. “This is a policy that if enough big companies with big rooftops decide to go for it, it means solar can be a bigger part of that 25 percent.”

The commission also increased the credit for net-metering customers who sell electricity back to the utilities from a wholesale rate to a retail rate.

Another key change, supporters said, is that customers who sell back to the grid can accumulate credit throughout an entire year whereas previous rules required utilities to balance accounts at the end of each month.