Hawai'i has become the first state in the country to require the installation of solar water heaters in new single-family homes.

Gov. Linda Lingle yesterday signed into law a bill requiring home builders to include solar water heaters in new single-family dwellings beginning in 2010.

"We've always talked about Hawai'i being a role model, and here's a case where we actually are," said Jeff Mikulina, director of the Sierra Club, Hawai'i Chapter.

The measure, Act 204, has been lauded by some environmentalists and others who said it is a critical move in reducing Hawai'i's use of fossil fuels and that it would significantly cut electricity costs for new homes.

Some in the solar industry, however, have said such a mandate eliminates homeowners' right to choose how to power their homes, and developers have warned it would drive up home building costs. Opponents have also criticized the legislation because it restricts the state tax credit for solar water heaters to homes for which a building permit was issued before 2010.

The new law prohibits the issuance of building permits for single-family homes that do not include a solar water heater system beginning Jan. 1, 2010.

Variances would be allowed if an engineer or architect finds that solar would be impractical because of insufficient sunshine, if it would cost more than would be saved by lower utility bills or if an alternative renewable energy system is used.

The act also allows home builders to use gas-demand water heaters if the home includes another gas appliance.

The Public Utilities Commission would set standards for the water heaters.

"This solar power legislation is another important step in our long-term plan for energy independence in Hawai'i," Lingle said.

"In addition to solar, it is critical that we continue to develop innovative energy solutions that capitalize on our natural renewable resource advantages in order to achieve our goal of having 70 percent clean energy in Hawai'i by 2030."

Lingle's office expressed concerns about some provisions in the measure, including the elimination of an existing tax credit for solar water installations in 2009 for residential developers.

The administration said it will introduce legislation next year to address that and other concerns.