All new homes in Hawaii will be required to have solar water heaters installed starting in 2010 under a law approved by the Legislature.
Hawaii becomes the first state requiring the energy-saving systems in homes.
Solar water heaters typically cost home buyers about $5,000 extra on their mortgage, but island residents will save thousands of dollars over the years on their electricity bills, supporters said.
"We owe to our children and grandchildren the promise of a clean and renewable energy future," said Rep. Hermina Morita, chairwoman of the House Energy Committee. "A solar water heater mandate in new home construction ... will result in greater public benefits to everyone at large."
Solar water heaters reduce residents' electricity costs between 30 percent and 35 percent — up to $150 per month for a family of four on Kauai, said Morita, D-Hanalei-Kapaa. With those kind of savings, their initial expense is usually paid off in three to four-and-a-half years.
Opponents of the measure said it would unfairly drive up costs to home buyers.
Lawmakers described a government requirement for solar water heaters as a way to protect the environment, reduce Hawaii's heavy reliance on foreign energy sources and save money.
"There are significant and quantifiable environmental benefits, energy security benefits and economic development benefits," said Sen. Gary Hooser, D-Kauai-Niihau. "This measure lowers the net cost of home ownership and will cost nothing in terms of the state budget to implement."
The bill passed unanimously in the House and 23-2 in the Senate.
The bill also ends current state solar tax credits beginning in 2010 worth about $2,500 in savings on purchases of solar water heaters.
Some legislators said they weren't comfortable with a law that takes away residents' ability to decide for themselves what kind of water heater they want to buy.
"Our country was founded on the principles of freedom and liberty," said Rep. Colleen Meyer, R-Laie-Kahaluu. "More and more, these dictates are coming down to the people saying, 'You have no choice anymore. You have to do what is politically correct.'"