The increasing popularity of solar panels is prompting environmental groups to call for lifting what they describe as arbitrary limits on a key program designed to encourage renewable energy use in Massachusetts.
So-called "net-metering" allows homeowners, businesses and local governments to sell excess solar power they generate back to the grid in exchange for credit on their bills.
Renewable energy advocates say 171 communities across the state have already reached the cap. They say that's slowing the state's efforts to reach its goal of 1,600 megawatts of installed solar capacity by 2020.
"We want to make sure that we can get as much solar power in Massachusetts as quickly as possible," said Ben Hellerstein, state director of the advocacy group Environment Massachusetts. "We don't have time to waste."
While individual homeowners are exempt from the cap, it's making it harder for larger projects and residents of apartment buildings to benefit from the program, Hellerstein said.
The cap is calculated as a percentage of each company's highest historical peak load - the most electricity consumed by their customers at any one time. Private facilities are capped at 4 percent, public facilities at 5 percent.
Norton Town Manager Michael Yunits said he's worried the cap is jeopardizing a large solar array planned for a former landfill in town.
Yunits said if the state doesn't raise the cap, the project developer could pull out, costing the town an estimated $300,000 a year.
"We've been planning this for two years and to suddenly have everything end now would be a disaster," Yunits said. "There are a lot of other towns looking into the same thing."
Sen. Jamie Eldridge, D-Acton, has filed a bill to raise the net-metering cap, allow an exemption for any project of 1 megawatt or less, and create a tax exemption for "community solar" projects that let residents of apartments or businesses that aren't able to install rooftop solar panels create offsite arrays.
It would also set a solar energy goal of 9,500 megawatts - or about 20 percent of the state's energy usage - by 2025.
Eldridge said the existing net-metering cap has already been hit in communities in much of eastern Massachusetts served by National Grid.
Mary-Leah Assad, a spokeswoman for National Grid, said the utility supports the growth of solar energy at the right price, but is concerned that customers without solar panels are helping foot the bill for those who use net metering.
"When people net meter, the costs of the wires and polls that they're using - they're not paying for that. The costs get shared by others without solar panels," she said. "We believe that a new set of policies need to be developed."
She said the company doesn't think that lifting the cap is the right policy.
Gov. Charlie Baker is also skeptical.
Billy Pitman, an aide to Baker, said in a statement that the administration doesn't support raising the net metering caps, but is committed "to reform the solar incentive system in a manner that balances the Commonwealth's solar market and achieves the state's solar objectives."
Baker supports the goal - set by former Gov. Deval Patrick - of achieving 1,600 megawatts of solar in Massachusetts by 2020. Massachusetts has already installed about 881 megawatts of solar electricity.
The administration said even without changes to the net metering cap, the state is on track to hit the 1,600 megawatt goal by 2018.
U.S. Sen. Elizabeth Warren, a member of the Energy Committee said she supports the use of solar panels and wind turbines - the so-called "distributed generation" of energy as opposed to single power plants. She said net-metering is an important part of that distributed energy system.
"Distributed generation makes our whole energy system more resilient as well as greener, and that's something we need to push here in Massachusetts and across the country," Warren told The Associated Press on Friday.
William Craven of SolarCity, a solar installer in 18 states, said other states routinely raise net-metering caps in response to increased demand. He said leaving the caps in place discourages the adoption of solar energy.
"In our view, the cap is completely arbitrary," said Craven, who is also a representative of the Alliance for Solar Choice, an industry trade group. "People don't want to see an industry stopped because it's so popular."