In the yard of a rambling 1930s bungalow on Trinity Avenue, a "food forest" grows: Asian pears, peaches, blueberries and a slew of vegetables including lettuce, artichokes and asparagus.

In the backyard sits a solar oven, where you'll often find beans, or another slow-cook meal simmering in a porcelain Dutch oven.

And on the roof -- yes, the roof -- kitchen herbs abound near the large solar panels that make much of what Stephen and Rebekah Hren do possible: live without carbon.

The couple bought the house in 2006 and has since outfitted it to operate purely on solar panels. The panels are tied to the utility grid of Duke Energy, which allows them to sell excess solar power to NCGreenpower, a nonprofit that pays renewable energy producers.

"For the first two years we were here we weren't tied to the utility grid, and functioned off a battery bank and solar power for electricity," Rebekah said. "But it is more efficient, and better in general for the planet, for us to be able to sell our excess solar power, so it feeds into our neighbors' houses when we aren't able to use all of it."

Rebekah, 33, is a certified electrician specializing in solar power, and Stephen, 34, has been restoring old homes for years.

Both enjoy gardening but have received a lot of expert help from their friends and tenants Keith Shaljian and his partner, Kyra Moore. They're the founders of Bountiful Backyards, a group that plants edible gardens. They live in an apartment off the back of the house, which is nearly carbon-free as well.

"I put the first garden bed in the very first day I moved there," Shaljian said. "Beauty is a really important element."

The Hrens wrote a book about their endeavor titled, "The Carbon-Free Home: 36 Remodeling Projects to Help Kick the Fossil-Fuel Habit." It was published by Chelsea Green in 2008.

On Sunday their home is open to the public for free tours from 10 a.m. to 4 p.m. Signed copies of their book will be for sale for $35.

The couple built a solar home from scratch in Person County years ago but realized they were hardly helping the environment with their commutes. Durham appealed to them with its central location (in-fill is friendlier to the earth than new construction), as well as the vibe of the community.

Caddy corner to the home is an apartment complex, and just blocks away sits the ghost of one of downtown Durham's industrial hubs.

The Hrens chose the Trinity Avenue house because it's close to the Durham Farmers' Market. Stephen serves on the board of the Durham Central Market, a planned neighborhood cooperative grocery that hopes to establish a place in Durham Central Park akin to Carrboro's Weaver Street Market.

They also wanted to set an example.

"I think what we are doing is important because it is in such a high-traffic urban area, not way out in the sticks," Rebekah said.

"All the projects we have done are on a totally normal house, not some fancy 'green built' home that cost $500,000," she said. "All the energy efficiency projects we did cost about $40,000, and we got tax credits of nearly $15,000 off that initial cost."

Plus, she said, "our solar panels will last at least 25 years!"

Most of the home's carbon-minimizing tweaks relate to the solar panels, but the superficial changes were done with environmentally friendly materials whenever possible.

"The structure's the same," Rebekah said. "We haven't really modified it."

The funky wallpaper in the living room is 50 percent recycled, the built-in shelves that line one entire wall were made by a local carpenter, and the tiles lining the wall behind the wood-burning stove were reclaimed from a home in Hillsborough.

The kitchen sports the most innovative changes to the home, they said. They use the top of the wood-burning stove as a griddle -- it stabilizes around 400 degrees, and they know which areas are cooler and which stay hot.

They also use an ethanol stove as seen in boat cabins, as well as an induction burner that runs off the solar grid -- they have to use copper-bottomed pots, but the burner boils water quickly.

They love the solar oven in the backyard, but Rebekah admits she misses an indoor oven. They take a tremendous amount of energy, however, and she has learned to embrace the toaster oven instead.

Their other appliances are all Energy Star, a government-backed efficiency program, and like the rest of the home they use solar power.

The wood-burning stove provides much of the home's heat, and they simply do without an air-conditioner in the summer, instead using passive cooling methods such as planting trees near windows that provide shade in the summer and let sunlight through in the winter.

The garden is still a work in progress, they said, but it has come a very long way. The Bountiful Backyards team has helped install rain-water collecting systems and does not use any chemicals in maintaining the plants. They instead grow other plants that repel pests.

"We've slowly been conquering parts of the yard," Stephen said.

Their friend and tenant, Keith Shaljian, said he's really not all that inconvenienced using mostly solar power -- namely, shorter hot showers from time to time.

"The sacrifices are pretty small," he said.