Which utilities are spending the most on demand response? A really useful new report from ZPryme (PDF) lays out the top ten utilities in the U.S. in terms of spending on what it calls “demand side management” over the past five years. Little surprise that California utilities are in the lead, given the state’s need to balance its increasing load of intermittent renewable energy sources like wind and solar power under the state’s aggressive renewable mandate. Pacific Gas & Electric spent $586 million last year, and has been the top spender since 2008, when it outpaced Southern California Edison, which spent $494 million last year. California is setting up new programs that should open new markets to demand-side resources, and it’s also connecting demand response and energy efficiency programs. Florida Power & Light came in third with $200 million spent on DR last year, and San Diego Gas & Electric came in fourth at $144 million. While big demand response aggregators like EnerNOC, Comverge and Constellation Energy are growing their share of the U.S. market, most demand-side management in the country is still carried out via utility programs. Big changes are afoot in the demand response industry, with federal rules set to open energy trading markets to demand-side “negawatts” for the same prices generated energy can get — I’m curious to see how that impacts utility spending on DR programs going forward.