HOUSTON, July 25 (Reuters) - Calpine's two new natural gas-fired power plants in California will begin commercial operation in a few days to replace lost nuclear output and to help meet renewable energy goals, the company said on Thursday. Calpine, the largest independent power producer in California, said its 429-megawatt Russell City Energy Center near Hayward, and the 309-MW Los Esteros Critical Energy Facility near San Jose will be completed in days, just ahead of California's traditional summer peak demand period. The California power grid expects about 2,000 MW of new gas-fired generation to come online this year, according to the California power market monitor's report. New generation will help bolster the state's power supply following Edison International's decision to decommission, rather than repair, the crippled San Onofre nuclear station in Southern California. As more wind and solar generation comes online to meet the state's 33-percent renewable mandate by 2020, the grid agency is looking at the need for back-up gas generation to maintain grid reliability. Calpine's more efficient power plants in the western United States produced 17 percent more electricity in the second quarter this year compared to 2012, due to the state's effort to reduce carbon emissions from other older plants and lower output from hydropower plants, Calpine President Thad Hill told investors on a call on Thursday. Hill said he is encouraged by a number of regulatory discussions now underway in California to boost new supply, along with other state goals related to air emissions and water use. "We are encouraged by the dialogue and the level of dialogue and the multiple venues," Hill said. "The devil will certainly be in the details, but the trend of the dialogue is the right way."