If Neighbor A puts a solar panel on his roof, and Neighbor B's oak grows and buries it in shadow, who has to pay to trim the tree?

In Pittsburgh, as in many other cities, there's no ready answer to that, and not much reason to worry about it. But city officials are starting to think about such questions -- and to plan for partial solarization of a fire house -- as an 18-month effort to harness sun power gets cooking.

"This is about more than a single project. It's about more than implementing a solar panel. It's about creating a solar infrastructure," said Mayor Luke Ravenstahl. "We want everyday people, whether it's a homeowner or a small business owner, to be able to" go solar.

A few score city building inspectors, planners, engineers and redevelopment officials, plus some business and academic professionals, gathered yesterday on the South Side for an all-day seminar on using sun power at city buildings, and removing barriers to solar-powered private development. The seminar follows the federal Department of Energy's June 2007 designation of Pittsburgh as a Solar America City, which brought $200,000 in grants and an equal value in technical help.

By fall, the city plans to put a solar water heating system on a firehouse in either Observatory Hill or Westwood, as what Mr. Ravenstahl hopes will be a model for more installations.

Such heaters are one of the better solar investments. It takes only five to seven years for a solar water heater to save more money than it cost, even though a backup heat source is used in the winter, said Stephen Lee, interim head of Carnegie Mellon University's School of Architecture and a solar researcher, who attended the seminar.

Installation of the heater could help encourage local electricians and engineers to learn solar installation, Mr. Lee said.

"The critical component in getting solar, beyond the money that's involved, is being able to call up an installer that can assist you," he said. "If you decided tomorrow that you wanted to put a solar array on your house, you would probably be pretty hard-pressed to find an installer to do that."

Also critical: having a regulatory system that tells people how to go solar without violating development rules. The word "solar" appears just once in the city code, in a provision allowing sun-powered energy systems in residential areas.

Sandia National Laboratories, a New Mexico-based consultant picked by Washington to advise the city, is helping city officials figure out how to regulate solar development. Jim Sloss, city energy and utilities manager, is hoping Sandia will bring answers to questions like the one about the tree and the solar panel.

Is this all crazy talk in a town that cracks the top 20 on cloudiest cities lists, where the five-day forecast sometimes lacks even a ray of hope? Well, Pittsburgh won the federal designation in part because it "didn't have the best sun," as Thomas Kimbis, director of market transformation for the Department of Energy, politely put it yesterday -- but he said the city's enthusiasm shines brightly.

"One common misperception about solar in the United States is that it only works in the Southwest or Florida," Mr. Kimbis said at the seminar. He said Germany is considered the leader in solar installation.

"We have quite a lot of sun here in Pittsburgh compared to what they have in [parts of] Europe."