In a milestone for renewable energy, California is expected today to make the largest investment in solar power of any state in U.S. history.

Ending more than two years of debate among political leaders, the state Public Utilities Commission is scheduled to take a final vote on a plan to spend $3.2 billion to provide rebates over the next 11 years to homes, businesses, farms and public buildings that install solar energy systems.

Closely based on Gov. Arnold Schwarzenegger's ``Million Solar Roofs Initiative,'' which died in the state Legislature last year, the new initiative will roughly triple the annual amount of state funding to subsidize solar power by tacking a new fee of about $1.10 a month on utility bills.

The goal is to install solar energy on 1 million buildings statewide by 2017, generating 3,000 megawatts of electricity -- the equivalent of six large power plants, or enough to serve 2.3 million people. By comparison, all the solar power installed in all 50 states today has a capacity of about 400 megawatts.

``I'm hopeful we'll be a trailblazer and we'll have other states joining us,'' said Dian Grueneich, one of the five PUC commissioners.

``We're confident this will bring solar from a fringe industry into the mainstream.''

Most customers' bills will remain about the same, Grueneich said, because a similarly sized fee, put in place in 1996 to fund energy deregulation, is expiring.

The subsidy generally would pay about one-third of the costs for people wanting to put solar power on their homes or businesses. A typically sized home solar system of about three kilowatts costs about $27,000 to buy and install. The new program will pay $2.80 a watt toward that cost, or about $8,400 for the standard system.

Schwarzenegger and a majority of the five PUC commissioners have expressed support for the program. The governor ran for office promising to increase solar power in California, but his plan died last year in the Legislature when labor unions insisted that high ``prevailing wages'' be paid on all solar installations. He then retooled the plan so that most of it required only PUC approval.

Environmentalists and solar industry groups were jubilant. They said the plan, dubbed the ``California Solar Initiative,'' will cut smog, reduce the burning of fossil fuels that contribute to global warming and provide enough consistency to encourage long-term investments in solar power manufacturing.

``Solar has always been the little cousin left out. It always has been pitted as this boutique, niche technology for backwoods hippies or Malibu millionaires,'' said Bernadette Del Chiaro, clean energy advocate for Environment California, a conservation group.

``The cost is staying high because the demand is low,'' she added. ``The only way to get the price down is to drive up demand for the panels.''

In the past several years, demand has been growing. Germany and Japan are installing the most, passing the United States as the world leader, largely because those nations, which signed the Kyoto global warming treaty, are offering huge incentives for renewable energy.

In Silicon Valley, venture capital firms have increased their investments in renewable energy -- including fuel cell, battery and solar technologies. VC firms invested a record $425 million into clean-tech start-ups during the third quarter of 2005, according to the Cleantech Venture Network.

``The interest in solar power in Silicon Valley is higher than almost anywhere in the country,'' said Barry Cinnamon, president of Akeena Solar, a Los Gatos solar installation firm.

``It is a combination of the price of electricity and the forward-thinking mentality where people are looking for high-tech solutions to environmental problems,'' said Cinnamon, a former software entrepreneur who founded the solar company in 2001.

Last month, the PUC approved a $300 million solar program for 2006. Today, it is expected to approve $2.9 billion more to be distributed to customers of Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric from 2007 through 2016.

Critics of the new program said the costs exceed the benefits, because solar power still costs three or four times as much as electricity from natural gas plants.

``Large energy users are going to be saddled with a disproportionate share of the program costs,'' said Joe Lyons, a lobbyist for the California Manufacturers and Technology Association. ``And we already pay the highest electric rates in the West.''

Frank Wolak, a Stanford economics professor who specializes in electricity, said he has other worries.

``Who is going to be taking advantage of this subsidy?'' Wolak said. ``Not poor people who live in apartments, but rich people who live in big houses. But under this policy, the poor will be subsidizing the rich.''

The PUC set aside 10 percent of the funding for low-income applicants.

Two other parts of Schwarzenegger's solar hopes still need approval from the Legislature. One would require developers to offer solar as an option on all new homes. The other would expand the number of people who can sell power back to the utilities when they generate more from their solar panels than they use, an idea resisted by many utility companies.

Supporters said the PUC plan makes sense for consumers in the long term, given rising natural gas and electricity prices, even though solar remains more costly than other forms of energy.

``With solar, you lock into your power rates forever,'' said Noah Kaye, a spokesman for the Solar Energy Industries Association in Washington, D.C. ``It's like buying a car with all the gasoline you'd ever need.''