San Francisco Mayor Gavin Newsom is expected to sign the largest U.S. municipal solar-incentive program into law Wednesday.

According to the mayor's schedule of public events, he plans to sign the ordinance at a press conference at 11:45 a.m. Pacific with San Francisco Assessor-Recorder Phil Ting and Supervisor Bevan Dufty.

The Board of Supervisors last week voted to approve the program, which sets up between $2 million and $5 million in subsidies for solar installations annually for 10 years (see San Francisco Offers Solar Subsidies and San Francisco Subsidy Steps Closer).

Once signed into law, the incentive will provide $3,000 to $6,000 for residential solar installations and up to $10,000 for commercial installations.

The vote came less than three months after a smaller one-year program was halted - only a few days before it was scheduled to begin - because of budgetary concerns (see Solar Setback in San Francisco).

Jose Tengo, a senior manager for Akeena Solar, called the program a model of how cities can help increase solar adoption.

"Where we see real change happening is at the local level," he said last week after the board vote. "As we deal with ... the fight we are having at the federal level over the [investment-tax credit], at the end of the day it's local leadership that will make inroads into expanding renewable energy."

The industry has been struggling for months to extend federal renewable-energy incentives, set to expire at the end of this year, but hasn't been able to get a bill past both houses of Congress.

Incentive bills have failed by a few votes time and time again in the United States (see Senate Blocks Renewable Incentives Bill, Policy Roundup: U.S. Senate Passes Incentives, Solar Roundup: Another Tax-Credit Proposal, Solar Sharpens Weapons for Incentive Battle, Solar Industry's Five-Step Plan, Renewable Tax Incentive Still At Risk, Senate Rejects Green Incentives to Pass Energy Bill and Senate Sends Energy Bill Back to Beginning).

Supporters in the Senate fell eight votes short of the votes needed to end a filibuster on the matter Tuesday after falling 10 votes short last week.

"It perplexes us as to why the investor community has continually hoped for the passage of this bill over the last 12 months," Thomas Weisel Partners analyst Jeff Osborne wrote in a research note last week, adding the firm expects it will take a new presidential administration to push through legislation that extends incentives for multiple years.

-- Reporter Rachel Barron contributed to this story.