In neighborhoods across the country, there's a battle brewing: the environmentalists vs. the aesthetes.

As "green"-minded homeowners move to put in new energy-efficient windows, solar panels and light-reflecting roofs, they are bumping up against neighbors and local boards that object, saying the additions defy historic-district regulations, will look ugly or damage property values.

In upstate New York, neighbors fought the installation of a wind turbine tower on a resident's 11-acre property, delaying the project by nearly a year.

Even former vice president and outspoken environmental advocate Al Gore had trouble getting solar panels and a geothermal unit approved for his Nashville home. A local zoning board initially wouldn't consider the application for the solar panels. It then took an appeal, several redesigns and a property inspection before they were approved eight months later. (The community recently revised its ordinance to allow the devices.)

David Bannatyne was tired of the drafty, stubborn windows in his early 19th-century home in Concord, Mass., and was especially fed up with paying his $5,000 heating bill each winter.

But when he applied for permission to put in 17 new, energy-efficient windows last fall, the town's Historic Districts Commission denied his request, concerned that the windows wouldn't blend in with the home's historic character.

After some debate, Bannatyne agreed to restore the windows instead. While he says they're now easier to open, he says his heating bills haven't changed. "I'm not doing the global-warming issue any favors by keeping these windows," he says.

Environmental groups say that the often burdensome and contentious process for those who live in regulated developments or historic districts prevents more people from making energy-saving changes to their homes.

"It's a hurdle. If people know there's such a delay, they say, 'Forget about it,' " says Nils Petermann, a research associate with the Alliance to Save Energy, a nonprofit advocacy group based in Washington, D.C.

The clashes come as states and utilities are increasingly offering incentives for energy-efficient improvements. At the same time, the number of designated historic districts and homeowners associations continues to grow, and with them the number and scope of local governing bodies that can restrict the changes people make to home exteriors.

There were 412,900 locally designated historic properties reported in 2006, up from 304,000 five years earlier, according to the office in the National Park Service that encourages local preservation.

And the number of condominium, co-op and homeowners associations -- which are usually governed by an elected board of residents and can control everything from pets to exterior paint color -- has grown to about 300,000 from 240,000 five years ago, according to the Community Associations Institute, an education and advocacy group based in Alexandria, Va.

Because the issue of green improvements versus aesthetics is cropping up in communities around the country, the institute earlier this year put together a committee to review its policy guidelines on energy-efficient improvements.

"Renewable energy and aesthetics don't have to be mutually exclusive," says institute spokesman Frank Rathbun. "But agreeing to projects without regard to the architectural guidelines of the community can create divisiveness and can affect property values."

In the case of Bannatyne's windows, local officials point out that restored windows can be just as energy efficient as new ones if done properly. And they say windows, especially, preserve a building's historic value, says Carol Kowalski, the town's staff planner at the time of Bannatyne's application.

"The worst things you can do to a historic building, besides arson, is take out historic windows," she says.

Some states are trying to make energy-efficient improvements easier. California has long restricted homeowners' associations from blocking solar-panel installations, and New Jersey and Arizona passed similar legislation this year. A bill in Connecticut would override zoning restrictions and make it easier for people to put in wind turbines on their property. It wasn't passed, but lawmakers hope to revive it next session.

Responding to concerns about aesthetics, some companies have been introducing products designed to be unobtrusive. Atlantis Energy Systems Inc. in Poughkeepsie, N.Y., is expanding its line of solar roof tiles -- which generate solar energy but are cut to look like standard roof tiles, instead of the traditional single solar panel.

Energy-efficient window-makers, too, are pitching products that blend in with older homes: Jeld-Wen Inc. this year introduced a new double-hung window that can fit into existing older frames but still provide better insulation.

Houston-based Standard Renewable Energy uses a racking system that positions solar panels to look flush against the roof. The company provides homeowners with a complete "green" service -- from consultation to installation of items like solar panels -- and will also go before an association or zoning board to help sell the project.