Prof's solar home feeds into local power grid

May 10, 2001

by Terry Devitt

When it comes to living lightly on the planet, Jean Bahr practices what she preaches.

Bahr, a professor of geology and environmental studies and an international authority on ground water, has become the first Madison home owner to generate electricity from the sun and feed it directly into a local electrical grid.

This spring, workers finished installing an affordable, practical system in Bahr's Nakoma Road home that transforms light from the sun into electricity, enabling her to meet a significant portion of her own electrical needs and feed excess electricity into the Madison Gas and Electric power grid.

"I've been interested in renewable energy for a long time," says Bahr, whose new sun-powered electrical system mirrors demonstration systems being installed in the addition to the Arboretum's McKay Center and at the Society of Friends meeting house off Monroe Street.

Solar technology, says Bahr, has come a long way, becoming far more efficient and affordable for the average consumer. But Bahr's primary motivation is reducing the amount of the greenhouse gas carbon dioxide that's pumped into the atmosphere by fossil-fuel burning power plants.

Moreover, as a byproduct of utility deregulation, power companies are now required to purchase excess electrical capacity from even the smallest generator of power through parallel-generation agreements.

"Ten years ago, a system like this would have been completely out of reach for me. Now, the cost is about as much as a small car," Bahr says.

The combination of greater efficiency, lower cost and the ability to feed the local power grid makes the technology practical in urban settings for the first time, she says.

At the heart of the system on Bahr's home is a 280-square-foot grid of flat, shingle-like solar strips. The solar shingles consist of layers of film, each sensitive to a particular range of wavelengths. The roof grid transforms that sunlight into direct current. The current is routed to an inverter, a device that transforms the direct current into the alternating current that powers household appliances.

The cost of the entire system, says Bahr, was about $16,700 and, at peak generating capacity under full sunlight, it can crank out 1,600 watts an hour. Bahr estimates that she'll be able to generate about 2,000 kilowatt hours per year, about half of what she consumes now.

"I'm not a big user. I don't have an air conditioner, which is probably the biggest single use of electricity in a home. I use a lot of compact florescent bulbs and I'll be getting a new energy-efficient refrigerator this summer," says Bahr.

"I'm not denying myself anything I need and if we're going to get things like this to take off, we can't expect the American public to dramatically reduce our standard of living."

A bonus is that excess capacity generated during the day feeds the local power grid when demand is at a peak. The spread of the technology to an urban environment could significantly reduce dependence on fossil fuels and limit the emission of carbon dioxide, a greenhouse gas and the chief suspect in the scenario of global warming.

"I didn't know until last summer that you could do this in an urban area and feed into the grid," she says.

Although Bahr had to cut through more red tape than anticipated with Madison Gas and Electric and insurance requirements, she praises the company for encouraging her solar initiative through its sponsorship of the Midwest Renewable Energy Fair and local demonstration projects. She attributes the excess of red tape to the fact that she was the first to sign on and that the language in the parallel-generating agreements is just now catching up with the technology that permits a homeowner to join energy producers.

"Once you have everything installed, it's kind of a seamless process. And, hopefully, the next person who does this will have an easier time of it."