PORTLAND — In the early ’80s, Tom Hard and Mary Lane Stevens built a solarium onto the back of their southeast Portland house. Sort of like a greenhouse, it passively catches sunlight and spreads warmed air to the rest of the house.

Electricity-generating solar panels, though, were another thing entirely. They always seemed far more futuristic, Hard says. And expensive. And involved complicated tax credits and other financial gizmos.

But when he saw solar panels going up on a neighbor’s roof, Hard says, solar seemed more down to earth. So he had warmed to the idea by the time he heard about Solarize Portland, a grass-roots effort to promote solar power. The plan: to persuade like-minded homeowners to go in on a bulk purchase of solar panels — and to get the best possible price. Hard and Stevens signed up.

“That gave us more confidence it would work in the Portland area,” Hard says. “We’re certainly not pioneers.”

If all that sounds about as exciting as a dim bulb, consider this: The program is on track to install panels on 120 homes in Portland since September, more than triple the 38 homes that had solar electric installations in all of 2008.

“It’s huge,” says Lizzie Rubado, residential program manager for the Energy Trust of Oregon. “I can’t tell you how exciting it is for solar in the Portland metro area.”

It started last spring, when Tim O’Neal was looking for a sustainability idea with broad neighborhood appeal. O’Neal works for Southeast Uplift, a nonprofit coalition of 20 neighborhood associations, and he provides logistical support for neighborhood sustainability efforts.

O’Neal was intrigued by the work of One Block off the Grid, a San Francisco startup that links groups of potential solar customers with solar contractors. One Block makes money from contractor fees.

Could volunteer-based neighborhood associations do something like that, O’Neal wondered.

Stephanie Stewart, active in the Mount Tabor Neighborhood Association, jumped at the idea. She worked with O’Neal to shape and market the southeast Portland neighborhood-based experiment. They met with the Energy Trust of Oregon, which committed to help. Five other neighborhoods joined in, distributing posters and spreading the idea by word of mouth through the summer.

The neighborhoods sought bids and selected a contractor, Imagine Energy, which as part of the job included ways to simplify the process. Before homeowners had to commit, Energy Trust ran workshops on how solar powers a home; how solar homes can buy as well as sell energy to the electric company; and the nuts and bolts of tax credits.

“Most people don’t know what a tax credit is, and they don’t know the difference between a deduction and a credit,” the Energy Trust’s Rubado says.

The workshops also helped shine a light on rainy Oregon.

Portland’s cloudy winters lead many to think it’s not a good place for solar panels, Rubado says. But in the course of a year, the city gets sunshine on par with the national average. The darkest place in Oregon, Astoria, gets more sun each year than the sunniest place in Germany, the world leader for solar installation.

But it does mean that on Oregon’s cloudy winter days — or months — homeowners will buy more power than they produce. In sunny August, though, homeowners could generate more than they use, which on a power bill looks like a credit when you overpay on a credit card.

Word of the program reached the doorstep of Hard and Stevens through their neighbor, Judy Crockett, a retired recycling specialist for the city of Portland, who also signed up for the solar panels.

The chance to save money by going through Solarize Portland — and to get help with both federal and state tax credits — sold the couple.

Energy Trust pays contractors for each system installed in the Portland General Electric and Pacific Power service areas, based on size. That reduces the initial cost to the homeowner.

A federal tax credit is good for 30 percent of the cost, not counting the Energy Trust subsidy. The state offers a Residential Energy Tax Credit of as much as $6,000. Most homes reach the cap, but the credit can be deducted over four years.

“The incentives at present for going this route are very generous,” Hard says.

For the couple, the math worked out like this: A $20,000 set of panels cost $14,000 after the Energy Trust discount. They’ll chip away at that outlay again, with $10,200 in state and federal tax credits, for a net cost of $3,800. Solarize Portland participants got a bulk rate 28 percent lower than the average price of solar panels, Rubado says.

If the 12 panels on Hard and Stevens’ roof churn out a forecast 2,200 kilowatt hours of electricity a year, that could account for more than half their annual electricity use.

If electricity rates rise about 2 percent a year, Solarize program participants can recover their installation costs in seven to 10 years, Rubado says. Hard, a retired Portland State University chemistry professor, says a 10-year payback would be fine with him.