With natural gas prices 30 percent lower in 2012 than 2011, the price of power on the California Independent System Operator\u2019s wholesale market decreased by 2.4 percent last year, according to the agency\u2019s annual market monitoring report. \tDespite lower costs of running fossil-fueled power plants, costs on the wholesale market increased in some areas due to San Onofre Nuclear Generating Station\u2019s continued outage. \tThe question of how much more was not quantified. \tThe agency \u201cdid not attempt to measure how much of the outage contributed to higher electricity prices,\u201d said Eric Hildebrand, director of market monitoring for the grid operator April 29. \tThat cost gets passed on to Southern California Edison and San Diego Gas & Electric customers\u2014the two investor-owned utilities responsible for the San Onofre plant. Edison is the operator and primary owner, SDG&E is a 20 percent investor. \tThe state\u2019s Division of Ratepayer Advocates estimates that increased costs are $54 million\/month for replacement power and grid services. \tThe grid operator also did not attempt to quantify any increased cost of support for renewables entering the transmission system. \tThe agency did quantify the price of derivatives exchanges on its \u201cconvergence\u201d market. In 2012 it was $56 million. \tWhile conceived as a hedging opportunity for generators, the convergence market in 2012 was \u201cby and large\u201d a financial instrument, not physical energy, according to Keith Collins, grid operator manager of monitoring and reporting.