California's groundbreaking efforts to encourage homeowners and businesses to install rooftop solar panels were so successful in 2012 that the program is now effectively winding down, according to a new report.

A record 391 megawatts of solar power were installed statewide in 2012, a growth of 26 percent from 2011, according to a report by the California Solar Initiative released Wednesday.

"The program has made solar affordable for ordinary Californians," said Susannah Churchill of the San Francisco-based solar advocacy group Vote Solar. "Solar is a classic California success story."

In January 2007, California launched an unprecedented $3.3 billion effort to install 3,000 megawatts of new solar over the next decade and transform the market for solar energy by reducing the cost of solar-generating equipment.

One megawatt is enough to power 750 to 1,000 homes. But because the sun doesn't shine all the time, solar industry experts say that one megawatt of solar can power about 200 households.

The California Public Utilities Commission's California Solar Initiative, known as CSI,provides rebates for residential and commercial customers of the state's three large, investor-owned utilities: Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric.

The initiative's road map calls for 1,750 new megawatts of solar power to be installed on residential and commercial roofs in the state by 2016.

Through the end of the first quarter of 2013, California had an estimated 1,692 megawatts of rooftop solar installed at nearly 168,000 sites, meaning the program is zeroing in on its goal. PG&E alone has 77,782 solar customers within its vast Northern California territory.

The aim of the incentives is to help solar achieve what's known in the renewable energy industry as "grid parity" -- the long-awaited point at which solar can compete with cheaper sources of electricity such as natural gas.

Since 2007, the average total installed cost for residential solar systems has decreased 32 percent from $8.77 per watt to $5.98 per watt. Those costs include labor and permitting, as well as the panels themselves.

Contact Dana Hull at 408-920-2706. Follow her at Twitter.com/danahull.