Rooftop solar  received a major boost in California with a new ruling from state regulators on May 24. The California Public Utilities Commission (CPUC) voted unanimously to reinterpret a cap on its net-metering program, more than doubling the potential amount of rooftop solar in the state.
Net metering  provides a financial incentive for small businesses and homeowners to install energy generation on-site, usually solar photovoltaic panels. Any electricity in excess of customer usage is sold back to the utility at the retail rate – higher than the wholesale rate earned by traditional generators. This is credited to the customer's bill to offset consumption from the grid when the customer's electricity demand exceeds their own generation.
However, the program was approaching a cap that the utilities were allowed to set. This limited each utility’s available net-metering capacity to five percent of its "aggregated customer peak demand." Utility companies had previously interpreted this to mean their highest overall demand on one particular day. Using this definition, Pacific Gas & Electric (PG&E), the state’s largest electric utility, was expected to reach its limit in 2013, after which it would no longer accept participants. The new decision expands the cap by defining "aggregated customer peak demand" as the sum of the highest electricity demand of each utility customer. This more than doubles the potential size of the program from the current 1.2 gigawatts (GW) to 4 GW, according to Environment California. This is about six percent of California’s net summer capacity.
Utilities oppose the expansion, arguing that by paying less or no money on their bills, net-metering participants are passing on their fair share of system costs onto other customers. These costs include payments for transmission grid upgrades and maintenance, low-income customer assistance programs, and municipal electricity systems. PG&E has 65,000 net-metering customers out of a total of 5.1 million.
Clean energy supporters and the solar industry say that the program has been critical in driving development of the industry. The net-metering program has already brought in over one billion dollars of investment to California. In a statement, CPUC President Michael Peevey said, "Today’s decision ensures that the solar industry will continue to thrive for years to come, and we are fully committed to developing a long-term solution that secures the future of the industry in California."
The CPUC will commission a study analyzing the costs and benefits of solar net metering, including its impact on nonparticipants. Unless new policies are adopted, the net-metering program will be closed to new customers on January 1, 2015.
California leads the U.S. in installed solar energy capacity, whether it’s distributed rooftop installations or utility-scale solar farms. Indeed, PG&E's net-metering customers alone represent one-third of U.S. total rooftop solar capacity. In 2011, California installed 542.2 megawatts of solar photovoltaic panels, the highest amount in the nation and more than doubling its existing capacity in 2010. Much of this is due to the state’s plethora of policies, rebates, and incentives at all levels of government, from utility loans to city-level rebates to the $3.2 billion state-wide California Solar Initiative. In addition, the state is home to over 1,000 companies in the solar industry, employing more than 25,000 people.
For more information:
CPUC Press Release: CPUC takes action to support solar by clarifying net-metering cap 
Wall Street Journal: California Expands Rooftop Solar-Power Program 
Solar Energy Industries Association: California Solar Fact Sheet  (pdf)
Clean Technica: 2011 U.S. Solar Market Report – Top 7 Findings & Charts