The Solar Electric Power Association has identified the utilities with the greatest amount of solar capacity, creating a benchmark to compare to in the future.

California has the largest solar capacity by far, but a number of other states found their way into the group's rankings, which list the top 10 utilities over overall, customer-side and utility-side capacity. Customer capacity is energy used for customers' onsite consumption or sold back to the grid. Utility-side is energy distributed by the utility.

The first annual report does not include specific figures for individual utilities, but the Association hopes to release more details next year. The group left specifics out due to concerns over private information and in order to get all the utilities involved in the survey.

More than 50 utilities were asked how much solar capacity they had at the end of 2007. In total, the utilities had capacity for 805 megawatts (MW) of solar energy. The top 10 represented 780 MW of that. Southern California Edison led the utilities by a wide margin, followed by Pacific Gas & Electric Company (Calif.), Nevada Power/Sierra Pacific Power, San Diego Gas & Electric Company (Calif.) and Xcel Energy (Colo.).

On the customer side, Pacific Gas & Electric Company swapped spots with Southern California Edison, followed by San Diego Gas & Electric Company, the Los Angeles Department of Water and Power, and Public Service Electric & Gas Company (N.J.). Customer-side generation totaled 345 MW, 331 MW of which came from the top 10. Customer-side growth is expected to reach 600 MW in 2012.

Southern California Edison again took first place on utility-side capacity, followed this time by Nevada Power/Sierra Pacific Power, Xcel Energy, Arizona Public Service Company and Tucson Electric Power Company. The top 10 represented almost all of the utility-side capacity for all utilities surveyed, accounting for 459 MW of the total 460 MWs.

The group's full report (PDF) also breaks the rankings down in separate lists for public and investor-owned utilities. It also looks at how the utilities compare when ranked by MW-per-customer, which slightly shuffles each list.

What the Association also found is that many utilities are investigating more customer-side installations, in which solar systems are sited on and feed into customer facilities, but owned by utilities. Utility-side capacity is also expected to increase in the coming years as large-scale projects that have been announced come online.

The southwest U.S. has the highest potential for solar generation, but in looking at estimated state solar requirements along with how much sun areas of the country receive, the Association expects the top 10 markets for solar in 2015 to be California, New Jersey, Arizona, New Mexico, Pennsylvania, Maryland, North Carolina, Nevada, Hawaii and Colorado.