On June 16 Hawaii governor Linda Lingle signed a bill requiring solar water heaters on all new homes in the state starting in 2010. Hawaii becomes the first state in the country to require the devices, which are part of a broad strategy to reduce the islands’ dependence on imported energy.

According to the Energy Information Administration, 90 percent of the islands’ energy is derived from petroleum, which is imported from Alaska or abroad. And while more than half of the state’s energy is used for transportation, petroleum-fired power plants supply three quarters of the state’s electricity. So rising oil prices have a far greater impact on the islands than other parts of the country. Officials hope to reverse those numbers, with the goal of generating 70 percent of the state’s energy from “clean” sources by 2030, according to a statement from the Governor’s office.

Solar water heaters have been around for decades. Their collectors are boxes with dark absorber plates that warm water using trapped heat from the sun. The systems can provide hot water and can also aid with general home heating, particularly with radiant systems.

The new measure could have a major impact on the state’s energy usage. According to Lane Burt, an energy policy analyst at the Natural Resources Defense Council (NRDC), after heat and air-conditioning, water heaters consume the second largest amount of household energy. “It’s very significant legislation. The technology is very simple and widely available,” he said. “It’s the low-hanging fruit of renewable technology. Some version of this legislation could be adopted by many other states.” He also argues that the act could have positive benefits for consumers. “I think the legislation will go a long way toward insulating homeowners from future utility price spikes,” he said. According to NRDC’s calculations, most solar water heaters pay for themselves in four to eight years. “Given Hawaii’s high energy costs, the payback time there is probably much faster,” he said.

There are exceptions to the requirement, including houses built in shaded areas and homes that include other renewable energy sources, such as photovoltaics.