With 2,220 MW of nuclear power still out of service and snow pack levels at historic lows, California’s electric grid operator unveiled what it hopes is a stable summer electricity supply-demand assessment for review by the California Independent System Operator (CAISO) Board of Governors.

With or without the return of the San Onofre Nuclear Generating Station’s (SONGS) two units, natural gas-fired generation is expected to be called on significantly during the peak-demand summer season. Gas plants account for about two-thirds (67.5%) of the state’s 50,341 MW of available capacity, CAISO noted in its assessment, which was issued Tuesday.

Although the state grid operator’s initial summer 2012 assessment showed adequate resources to handle nearly any combination of operating conditions, CAISO’s Keith Casey, vice president for market and infrastructure development, said the staff analysis was completed before recent announcements that indicated SONGS might not be available when the summer peak-demand season starts in June.

“We are working together with Southern California Edison Co. and San Diego Gas and Electric Co., as well as others, to develop mitigation measures should the SONGS units not return to service this summer,” said Casey.

The assessment noted that snow pack water content measured on March 1 was 30% of the April 1 average, and the state is facing “one of the lowest snow pack levels in history, even with recent storms.” Hydroelectric capacity is forecast to be about 1,137 MW below normal summer demand levels.

Casey said that the state may have to call on more demand response and interruptible load programs during periods of strain on the grid this summer. CAISO’s “Flex Alerts” could generate 1,000 MW or more of conservation.

“Looking beyond 2012 it will be critical for new generation additions to keep pace with anticipated load growth and generation retirements,” noted the assessment. “This will be particularly challenging in light of approximately 17,500 MW of [mostly gas-fired] generation capacity that is subject to once-through-cooling regulations requiring this capacity to be retired or repowered during the next 10 years.”

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