On the longest day of the year, the bright sunshine had the electric meter running backwards at Katharine Kilbourn and Scott Shear's house.

That's because eight months ago the couple installed a solar array on the roof of their 98 Brookside Ave. home. And while the couple says the solar panels are already making economic sense, the city picked their front yard to announce that it will sweeten the pot for other home owners who want to add solar panels.

"If you look at our meter now, it's running backwards," said Shear, minutes before Mayor Thomas Menino arrived to announce the program.

The new program is part of Renew Boston. It adds a city rebate to incentives already offered by the state and federal governments. The average residential rebate would run $1,000-$3,000, according to the city.

Kilbourn and Shear, who have lived at the house for 22 years, say they will get their $36,000 investment back soon. They already have a $10,000 federal tax incentive and received a $4,600 rebate from the state. They won't be eligible for the new city rebate, but even without it they say they are happy with their decision.

The solar panels produce 90 percent of the power required for their four-person household.

According to Jim Hunt, the city's chief of environment and energy, going solar will pay for itself in 3 1/2 to 4 years with the additional city rebate. With the federal and state incentives alone, payback time can be about 6 years.

Somerville-based SunBug Solar installed the couple's 4.6 kilowatt system. Another SunBug project, the Bartlett Square condos, is visible from the couple's home. That project includes both solar electric and solar water heating, according to Ben Mayer, vice president of marketing for the firm.

Hunt said the first step for homeowners interested in going solar is to schedule an energy audit through www.renewboston.org. Homes must be properly insulated among other requirements before seeing if solar panels make sense.

One Jamaica Plain resident, Loie Hayes, is in the process of getting quotes for installing solar panels on her Mission Hill home. Hayes, of the Boston Climate Action Network, said she is excited about the new rebate program. In the video above right she describes how to tell if your home is a good candidate for solar power.