The U.S. Senate passed an extension of the renewable-energy production tax credit Thursday as part of a bill intended to address the ailing U.S. housing market. The renewable-energy credit provides a per-kilowatt-hour incentive for the first 10 years a renewable-energy project is in operation — a credit considered to be a vital driver of clean-energy expansion. The credit is worth an estimated $6 billion and will be extended for another year, through 2009, if the legislation makes it past the House of Representatives and President Bush. Homeowners and businesses will also be able to offset up to 30 percent of the cost of solar and fuel-cell equipment under the bill, and homeowners who install efficient insulation, furnaces, and windows will get additional credits. “It would be difficult for taxpayers to find an investment that offers a better return,” said Melinda Pierce of the Sierra Club. “This package of incentives will pay us environmental and economic dividends for years to come.”