The managers of California's electric power system quickly issued public assurances about avoiding summer blackouts when Southern California Edison announced this month that it would permanently close its troubled San Onofre nuclear plant.
It was an easy call because they already knew that San Onofre, which has generated about 5 percent of the state's electric power, wouldn't be available this summer and had made plans to purchase power from other sources.
Even so, the state's supply margins will be tighter this summer than usual as air conditioner-driven consumption approaches 50,000 megawatts on hottest days.
A "summer assessment" from the Independent System Operator, the Folsom-based organization that manages the state's electric grid, says the reserve margin could dip to about 10 percent under extreme circumstances, leaving little room for an unanticipated loss of generation.
The situation is exacerbated by an improving economy that has raised power demand and by shortages in hydropower due to drought.
The more important question, however, is what happens after this summer. California's electrical supply picture is supposed to change as it implements the state's decree that by 2020, 33 percent of its power must come from "renewable sources" mostly solar panels, windmills and geothermal wells as a contribution to fighting global warming.
Dozens of solar projects, big and small, have been proposed. Investors have sunk many millions of dollars into design and permitting. But several of the larger projects have become insolvent, and environmental groups have opposed many of those in the Southern California desert, leading to permitting delays.
Something of a feud has erupted between environmentalists who embrace large-scale solar projects in the desert to meet the 33 percent goal and opponents who say solar should be on rooftops or "degraded land."
Even assuming that enough "renewable" projects are sited, permitted, financed and even built, another issue has emerged whether there'll be enough power from other sources to offset the inherent unreliability of projects that depend on the sun shining and the wind blowing.
San Onofre's shutdown sharpens that issue. Meanwhile, some plants along the coast are being told by regulators to do away with "once-through" cooling systems, and may be forced to close. But replacing them with new plants fired by natural gas which, though cleaner than coal or oil, is still a carbon dioxide emitter runs into regulatory problems as well.
Finally, the shift to renewable power, if it occurs, could be a negative factor in the state's business climate. It will drive California's electric power rates, already among the highest in the nation, even higher.