On a former landfill in Springfield, Massachusetts, 12,980 solar panels produce enough electricity to serve 850 homes. The Cottage Street project is one of three solar arrays in western Massachusetts that provide power to customers of the regional utility, Eversource Energy.

Taken together, these three projects produce more power than 40 percent of the entire installed solar capacity in the state of Maine.

Solar power is emerging as a key strategy to combat climate change and lower New England’s dependence on fossil fuels. Massachusetts has become a national leader in solar, while Maine is a middle-of-the-pack laggard.

For example: Massachusetts ranks first in the country this year for having the best financial and policy incentives for solar, according to Solar Power Rocks.com, an advocacy website for homeowners. Maine is ranked 28th, tied with Indiana.

Massachusetts is rocking the solar world in part because it encourages big projects that can produce lower-cost power, including some utility-owned generation that’s sold directly to customers. Maine law bans utility-owned generation, including solar.

In Maine, the ongoing debate over the future of solar energy is concentrated on small-scale, rooftop units and the rights of homeowners.

The potential benefits of big solar projects are overshadowed by the battle ramping up now at the Maine Public Utilities Commission over how to handle net energy billing, the decades-old practice of paying homeowners the full retail price of the surplus power they send to the grid. Sometimes called net metering, this practice is the key financial incentive that helps make solar electricity affordable to homeowners.

Whatever happens at the PUC, the outcome won’t do much to advance Maine’s overall solar standing.

In Massachusetts, nearly two-thirds of solar electricity is generated by commercial and utility-scale projects, according to data from the Solar Energy Industries Association. And since 2013, four times more solar output is coming from these larger projects than from home installations, figures from the Massachusetts Department of Energy Resources show.

These facts highlight an important perspective that’s largely missing in Maine, where the future of solar has deteriorated into a political spat between Democrats and Republicans over rooftop panels.

Utilities and Gov. Paul LePage say net metering forces other electric customers to subsidize solar for homeowners, a cost that will grow as more rooftop solar is installed. This view was at the core of LePage’s veto of a hard-fought solar energy bill last spring in the Maine Legislature, a veto upheld largely with the help of Republicans.

Solar advocates and their Democratic allies, though, point to studies that show net metering in its current form actually saves more than it costs. One of those studies was done for Maine’s PUC, and recently updated.

This dispute is happening in states across the country. Meanwhile, falling panel prices, government clean-energy policies and mounting evidence of climate change are leading to explosive solar growth in the United States.

As of March of this year, 27,455 megawatts of solar capacity were installed nationwide, according to the SEIA trade group. That’s enough electricity to serve 5 million average homes. More than half of it came from utility-scale projects. A quarter came from commercial, community and institutional-size projects. A final 23 percent was generated at residential installations.

In Maine, there’s plenty of political muscle behind the sector with the smallest capacity.

National solar installers that have built their business models on residential rooftop have emerged as active lobbyists in Maine’s net metering war. Sunrun Inc., a noteworthy donor to Maine political action committees, as well as Solar City, through a recently formed group called Energy Freedom Coalition of America, are key participants in the PUC case. The state’s solar installers also rely heavily on residential rooftop installations. They are backed by influential environmental groups, led by the Natural Resources Council of Maine.

The PUC has received more than 260 public comments on its case docket. Many come from residents who have installed panels on their homes or want to, citing concern for climate change and the environment. Many are form letters that begin: “Please reject any attempt to get rid of net metering in Maine.”

CONSTRICTED INVESTING

Maine’s 16-year-old electric industry restructuring law bans private utilities from generating any power, effectively keeping the well-financed parent companies of Central Maine Power and Emera Maine out of solar.

This policy has consequences, according to John Carroll, a spokesman for Avangrid, which owns CMP. Avangrid has 53 wind farms in 18 states and solar farms with a combined capacity of 50 megawatts in Colorado and Arizona. But a continuing legal challenge in Maine over the conditions under which utility affiliates could own generation is keeping Avangrid from directly investing in solar here, he said.

“Who are you benefiting by keeping out one of the largest, best-capitalized players?” Carroll asked.

Maine has 19.4 megawatts of installed solar capacity. One utility-scale project, Carroll said, could double Maine’s output.

“The problem is, we don’t have enough solar, not that we don’t have enough rooftop solar,” he said. “That’s why we’re lagging behind other states. We’re arguing about the best way to protect a really inefficient solution.”

The vast majority of the larger-scale projects being built or proposed in Maine are by private companies that have signed power purchase agreements to sell the electricity to specific customers or utilities, either here or out of state.

For instance: Publicly owned Madison Electric works has contracted for a 4.8 megawatt solar farm that can serve 880 homes. It will be built and financed through a partnership and power-selling contract that includes IGS Energy of Dublin, Ohio, and Pittsfield-based Cianbro Corp.

Ranger Solar, a Yarmouth-based startup, has submitted proposals for a giant, 50-megawatt solar farm in Sanford. The power would be sold in Connecticut, but the project is contingent on Ranger winning a regionwide, clean-energy bidding competition.

Dirigo Solar, which has an office in Westbrook, says it’s hoping to finalize power purchase agreements by year’s end with CMP and Emera to build solar arrays ranging from five to 20 megawatts. It won PUC approval to install up to 75 megawatts of capacity, enough to power 10,000 homes.

Community solar farms, in which homeowners buy a share of the generation from a big solar array, are another way solar could grow. But Maine law currently limits farm shares to 10 customers. An attempt to increase the number died with the failed solar bill.

ECONOMIES OF SCALE

While big solar tries to get a footing in Maine, a law in Massachusetts, updated last spring, allows utilities to generate up to 35 megawatts of capacity from the sun.

In addition to the 3.9 megawatt Cottage Street project, Eversource Energy owns the 2.3 megawatt Indian Orchard Solar project, which can serve 500 homes. It also is located on a former landfill in Springfield, and has 8,200 panels.

The oldest project is 1.8 megawatt Silver Lake Solar, located on formerly contaminated industrial land in Pittsfield, Massachusetts. The 6-year-old array has 6,500 panels and can serve 300 homes.

Eversource has plans under the revised law to build 70 megawatts of solar on company-owned land that will help lower customer rates, according to James Daly, the vice president for energy supply at Eversource. Daly said the company can build big solar arrays at an installed cost of $3 a watt, compared to $4.50 a watt for small rooftop installations.

“The biggest economies are the economies of scale,” he said.

It’s less costly to buy panels by the thousands, Daly said, and it’s cheaper to install them on the ground, rather than a roof. Eversource also realizes investment tax credits and can receive special capacity payments from the region’s grid operator.

But Steve Hinchman, the financing director at Maine’s largest solar installer, ReVision Energy in Portland, said there’s a difference between cost and value. While a variety of incentives may make utility-owned solar cheaper to produce, he said, locally sited solar has a greater value for Mainers.

Homeowners pay the bulk of the cost of installing rooftop solar, Hinchman noted, while ratepayers finance utility-scale projects. He also said customers end up paying the cost of renewable energy credits that utilities receive for producing or buying clean power. Hinchman noted that studies, including the recently updated one for the Maine PUC, show that the value of solar energy greatly exceeds what homeowners are being paid under net metering, especially at times of high electricity demand.

“When you generate power on a summer afternoon, you’re sending out more-valuable power than you are being paid for,” he said. “The utility’s position is ‘solar is only good if we own it.’ That’s a recipe to gouge ratepayers.”

Rooftop solar in Maine supports more than 56 companies and 330 workers who are involved in installing and servicing small-scale solar installations, SEIA data show. Rooftop solar gives homeowners control over their electric rates and a sense of independence. And with gains in battery technology and efficiency, some homeowners see a day coming when they can cut the utility cord and generate all their own power.

A newly formed group of solar installers and customers called the Solar Energy Association of Maine is asking the PUC to extend the net metering rule and protect existing customers. But the threat from climate change is so dire that Maine needs an “all of the above” approach, according to Steve Weems, who heads the group.

“We need a solar policy that supports small scale, intermediate and large scale,” Weems said. “All of it, in the interest in really moving the needle to a much greater penetration of solar.”