Solar has suddenly become much more important in Southern California because of the outage at the San Onofre Nuclear Generating Station (SONGS).

San Diego Gas & Electric (SDG&E), California’s third biggest investor owned utility, could lose fifteen percent to twenty percent loss of its base load electricity. “SDG&E, along with the California transmission system operator and Southern California Edison (SCE), are working together right now on contingency planning for the possibility that those two large units could be offline this summer,” said SDG&E spokesperson Jennifer Ramp.

SDG&E, Ramp added, will bring its new 500-kilovolt Sunrise Powerlink transmission line into service in early summer. Designed to deliver 1,000 megawatts of regional solar and wind that are not yet in service, Sunrise will carry extra fossil generation this summer -- if it is available.

But, Ramp said, “you could be looking at a very unique situation,” adding, “We could be asking our customers to conserve energy.” SCE, the nuclear power station operator, took the two-unit, 2,200-megawatt SONGS offline in January and announced this week it will not restart the more than quarter-century-old plant until worn and leaking tubes perform "in excess of industry guidelines."

Even before the power shortage threat from the SONGS outage, SDG&E had been studying the challenges of solar and the opportunities of energy efficiency as part of its smart grid and smart meter planning, said Lee Krevat, the utility’s smart grid program director.

“We had already planned a program for this summer called Reduce Your Use,” Krevat said. Through the program, the utility’s ratepayers will be rewarded for reductions in their electricity consumption. “On certain days when less energy is available,” Krevat explained, “for every kilowatt-hour less that customers use, we will rebate them 75 cents.”

Though the design of Reduce Your Use preceded the SONGS outage, Krevat said, “If there is an energy shortage, this will be a significant arrow to have in the quiver.” Not only will the program reward customers for conserving, he said, but SDG&E “will be able to leverage the smart meter program to verify that they conserved when they did.”  

SDG&E’s concern with solar, Krevat noted, is variability. That is a common concern at utilities. Though SDG&E understands objections to fossil fuels, it is reassuring to people who get blamed when the lights go out and the air conditioning goes off to have a base load source with which they are familiar.

Since 2001, SDG&E has annually increased its year-on-year installed solar capacity more than 35 percent, Krevat said, with growth of 40 percent in 2010 and 38 percent in 2011. After a decade of such growth, solar’s share of the energy mix is growing -- along with questions about the impact of its variability on system stability.

Utilities are comfortable with nuclear power’s always-on quality and the fact that with it they needn’t concern themselves about things that renewables require in order to serve well, like a loading order, geographic distribution, dynamic energy markets, and ancillary services.

But now, some of California’s nuclear is no longer on. And summer’s heat, along with the attendant surge in air conditioner use, is coming. Can solar help fill the gap?

An SDG&E study of a one-megawatt solar system “at the end of a feeder line in our service territory,” Krevat explained, showed a unique and potentially distribution-threatening kind of variability. A dynamic system voltage fluctuation not apparent in afternoon-long measurements of output, he said, looks severe if the measured output periods are smaller. In one-, five- or ten-second increments, the voltage fluctuations may be beyond the distribution system’s tolerance.

“A variability of voltage is detrimental to our equipment, could cause major outages, and is an issue we need to solve,” Krevat said. “We worked with a vendor to model a dynamic inverter, which is a new product.”

Krevat did not want to reveal the vendor’s name or precisely how the dynamic inverter worked. He said engineers were able to position the inverter in a way that partially alleviated variability.

“Eventually we were able to solve the variability in the voltage,” he said. “The belief of the engineering team was that the closer you put the solution to the problem,” he explained, “the better chance you have of fixing it.” But it did not prevent capacitors “from reacting in a way that would cause the system to fail” and “cause major outages to our customers.”

The utility’s engineers think all the time, Krevat said, about “how to have a circuit that gets to a large amount of solar. We would love to have an easy answer, but it is wholly dependent on where the solar installations are and how high a penetration there is. That is the broader problem we are trying to solve.”

The utility, Krevat said, will continue to model different circuit parameters in search of the solution. “The real emergency for us is that, with a growth rate that has exceeded 35 percent every year and an average in the past few years around 40 percent, we need to solve this before the issue becomes overwhelming to us.”

Depending on what happens at the San Onofre plant and in the heat of Southern California’s summer, “overwhelming” could be closer than many think.

“We don’t know if SONGS will or won’t be in service by summer,” Ramp said. “But you have to plan for contingencies. If SONGS remains down, that is a pretty major contingency.”