On June 7, California's grid operator (ISO) reported that the state had hit a new record for solar PV and concentrating solar power (CSP) generation, at 6.160 GW-AC. A little over a month later, a new peak was set on July 13, 1 MW shy of 6.3 GW-AC.
A new record was set two days after that, and throughout July and August records have been falling like dominoes. As the latest, California ISO reports that the state's PV and CSP plants reached a peak output of 6.391 GW-AC at 12:54 PM local time on Thursday August 20.
However, California ISO does not report the output of customer-sited "behind-the-meter" PV plants, including the state's rooftop residential and commercial solar. GTM Research estimates that in the first quarter of 2015 these comprised 3.2 GW-AC of capacity. While real-world output never reaches total capacity, this could theoretically put peak solar output near 50% higher.
California ISO has in the past expressed concerns about integrating such high levels of solar. These were most prominently expressed by grid operator in its "Duck Chart", which showed how high levels of solar output could lead to conflicts with baseload coal and nuclear power stations as early as 2018. The chart also suggested a need to swiftly ramp up huge volumes of flexible natural gas generation as solar output ramped down in the evening.
However, after utility Southern California Edison announced in 2013 that it would permanently close the last two reactors at the San Onofre Nuclear Generating Station there is only one nuclear power plant in the state, and new capacity coming online has been flexible gas, not coal or nuclear. In terms of the evening ramping challenge, a number of parties around the state and nation have been working on solutions.
In a 2013 document, California non-profit Clean Coalition showed how a variety of solutions, including importing and exporting power, demand response and energy storage could mitigate the need to ramp quickly. The study found that these solutions would be particularly effective when deployed together to flatten the back of the duck.
And in the years since this study, California has been moving many of these solutions, including requiring that utilities procure energy storage. State regulators have also been looking at ways to address these challenges on the demand side, including a new proposal to address multiple demand-side solutions with an integrated approach.
Another solution can be the deployment of concentrating solar power with thermal energy storage (TES). Abengoa's 280 MW Solana CSP plant in Arizona includes six hours of storage, which allows it to meet evening demand, and in Spain Torresol has built a CSP plant which can supply power 24 hours a day. However, TES is not included in the CSP plants which have been built in California.
These sorts of technical solutions will become more important as California considers Governor Brown's new goal for the state to get 50% of its electricity from renewable energy by 2030. At a recent Advanced Energy Economy conference, California ISO President and CEO Steve Berberich expressed confidence that it is technically possible to exceed this goal, and stressed demand-side solutions.
In the summer of 2015, such concerns are still years off. A California ISO chart from August 20th shows that the impacts of wind and solar shifted the peak in the remaining net load from 5 PM to 9 PM. However, this net load rose slowly throughout the day, with wind output rising in the evening as solar went off-line.