Whose is biggest?

“Ours!” claims Green Mountain Coffee Roasters.

“No, ours!” insists NRG Systems.

“Yeah, but ours has a hot feature,” adds National Life.

Each of these Vermont companies is touting its solar-power array — which goes to show that, to alternative-energy advocates, size does matter.

The competing corporate claims illuminate solar’s growing popularity in an often cold and cloudy state, one that might seem an unlikely growth area for this form of renewable energy.

Vermont actually has “tremendous sunshine,” says Leigh Seddon, vice president of engineering for Montpelier-based Solar Works. “We have 30 percent more annual solar radiation here than in Germany, which is number one in the world for installed solar.”

Several additional sun-power projects of various sizes are in place or planned in Vermont. Most of them were spurred by state and private utility clean-energy grants funded through the sale of the Vermont Yankee nuclear plant in 2002. Federal tax credits for installation of photovoltaic panels provide an added incentive to go solar.

Central Vermont Public Service, for example, plans to install a high-visibility, 50-kilowatt array outside its offices on Route 7 in Rutland. Green Mountain Power, the state’s other leading utility, has put a 58-kilowatt set of solar panels on its building in Westminster; it’s expected to provide 80 percent of on-site power needs. And Sen. Bernie Sanders has just announced a $5 million Pentagon appropriation for clean-energy initiatives at the Vermont Air guard base in South Burlington. Sanders says the package includes “the largest solar energy project in the state of Vermont.”

These and a number of smaller initiatives around the state mark a significant shift in attitudes toward solar power in Vermont, says Andy Perchlik, head of Renewable Energy Vermont. As recently as four years ago, utilities in the state “weren’t very enthusiastic about solar,” he notes. What’s changed, Perchlik suggests, is the economics of solar power, which is becoming increasingly cost-effective as prices of materials drop.

So, who’s really got the most juice in Vermont?

Green Mountain Coffee Roasters’ claim to be building “the largest solar installation” in the state is based on the number of PV panels — 572 — that its $750,000 project will include. But the panels’ estimated 100-kilowatt output will generate only about 1 percent of the energy consumed at the company’s Waterbury plant.

National Life aims to meet 10 percent of its headquarters’ energy demands through its 418-panel solar array, which will generate up to 73 kilowatts. Plus, the Montpelier-based insurance company plans to add a solar thermal set-up that will heat half the hot water used in the building.

But Perchlik says the top prize should go for now to NRG Systems, which is — perhaps ironically — a manufacturer of components for wind-power turbines. NRG’s 149-kilowatt installation on its Hinesburg campus will account for at least 60 percent of power consumed there, according to NRG spokeswoman Abby White.

“You usually rank solar by kilowatt size,” Perchlik says. “It looks to me like NRG’s is biggest.”