HARVARD -- To begin with, the Harvard Solar Garden group consisted of a few folks who were interested in the state-backed solarize initiative that offered low-interest, long-term loans to install solar panels on the roofs of residences or businesses. It would provide electric power directly, winding back their electric bills as payback for the energy they produced.

But not everybody who wanted to climb aboard could do so, in some instances because the roofs in question couldn't support the panels or because the site was unsuitable for solar. Either way, they were left out, birthing the garden idea.

"At least half the folks who were interested couldn't do it," Solar Garden principal proponent Worth Robbins said.

So they started thinking in terms of a group project that could tap into the Solarize Massachusetts program. At first, the state said no to a "commercial project," but then reconsidered, he said, creating a new category for community solar and offering the same deal.

Asked if there are any other such communal facilities that he knows of, Robbins said there's one on Cape Cod, "smaller than ours" but solely funded by investors who don't have a stake in the electricity it produces, as Harvard LLC members do.

Basically, Harvard Solar Garden shareholders purchase shares that range from 3,000 to 15,000 kilowatt hours, the maximum the state allows under the provisions of its Solar-2 grant program, which is the same set-up available to homes and businesses linked directly to the grid. In return, they get credits from National Grid that substantially reduce their annual electric bills, in many cases down to zero, Robbins said.

The state Department of Energy Resources wrapped the original solarize program in June, having met its 400-megawatt goal, but Harvard Solar Garden LLC was able to reserve a spot for its pending project. The deal hinges on the facility being up and running by June 30. Robbins said the group is prepared to meet the deadline.

The window for new investors to buy shares in the project will be open only for another month or so, Robbins said, with construction set to start as soon as materials for the freestanding foundations arrive.

Each panel array will be seated in a ground-mounted frame that rests on poles driven deep into the ground. The pole installation should start before the frost line settles in, but otherwise, construction is not weather dependent, he said.

Some have said it's a business with some out-of-town investors and as such not a "community" project at all, but Robbins clearly doesn't see it that way.

"The main thing is that the closer to full capacity we get, the more the costs are spread out," he said. He cited an operational to-do list that includes site maintenance and security, equipment upkeep and repair, monitoring and other expenses, as well as initial start-up costs. Which is why he's still out there stumping for the cause, in town and beyond.

The list of investors grew, with about 40 people on it now; all but one of them are town taxpayers, plus a few more from the recent presentation in North Hampton.