April 17 (Reuters) - A major California utility and General Electric Co on Monday unveiled a first-of-its-kind battery storage system that will enable instant power output from a natural gas peaking plant to accommodate the state's changing electricity needs while decreasing greenhouse gas emissions.

The system, which was installed at two separate Southern California Edison "peaker" plants this month, will give the utility increased flexibility as the large amounts of renewable wind and solar power required by state mandates have made energy generation cleaner but far less predictable.

Peaker plants are small power plants designed to come online quickly when power demand is high, such as on a hot summer day. But they are also among the least efficient resources available to the utility.

The 10 megawatt batteries, which contain cells made by Samsung SDI, are capable of providing power immediately, eliminating the need for the plant to burn fuel in "standby" mode. Prior to integrating the batteries, the 50 megawatt plant would take about 10 minutes to ramp up to a desired capacity.

Southern California Edison's president, Ron Nichols, said at an event to unveil the hybrid electric gas turbine in Norwalk, California that the new system would cut plant startups in half and reduce total run hours by 60 percent.

The systems will work particularly well as solar power drops off at the end of the day, just at the time when demand starts to rise as utility customers get home from work and begin running air conditioners or turning on appliances.

California is requiring its utilities to source half of their electricity needs from renewable sources by 2030. At the same time, the state has required procurement of energy storage systems to help integrate those renewables. Southern California Edison has brought several energy storage projects online, including a large Tesla Inc battery earlier this year.

The GE systems were installed at peakers in Norwalk and Rancho Cucamonga. The utility is considering adding the systems to three other peaker plants in its territory, Nichols said. (Reporting by Nichola Groom; Editing by Bill Rigby)