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Storage was the compelling story of 2021, according to our newly published Annual Stats

February 28, 2022


The clean energy transition is gathering momentum, and nowhere is that more evident than the California ISO’s 2021 Annual Statistics document, now posted on the News page of the caiso.com website. It plainly shows a continuing dramatic shift to renewable energy and stunning growth of battery storage resources on our power grid last year.

The most striking of the data illustrate the meteoric rise of battery storage on the system, a key component to supporting grid reliability during the transformation to a carbon-free electric grid. During the calendar year 2021, an impressive 2,359 megawatts (MW) of utility-scale battery storage capacity was added to our system. For perspective, that compares to 172 MW added the previous year, over 12 times more than the storage additions in 2020.

That’s important, because as California continues to dial back its carbon-emitting resources, more wind and solar generation is being added to our power mix. Those resources generate energy only when the sun is shining and the wind is blowing, so it’s imperative to have storage on the system to soak up energy while it’s abundant, and inject it back onto the grid when needed.

In fact, storage played a crucial role in alleviating stress on the system during tight energy supplies on July 9, 2021. Wildfires had reduced the amount of electricity coming over large transmission lines from the Pacific Northwest, while searing heat across the West caused spikes in demand. Even though much of the storage was new to the system and to the grid operators, the resource overall performed well and is credited with helping to avert rotating power outages.

The 2021 Annual Statistics also show that the California ISO power grid set records for solar and wind peaks and for the highest amount of renewables serving demand. Our newest solar peak was 13,205 MW, set on May 27 at 11:57 a.m., and wind topped out at 5,754 MW on May 29 at 10:12 p.m.

The statistics document also captures one of the year’s most promising and sensational harbingers of the clean energy transition for the grid and for California: Renewable energy served 94.5% of the load for a brief time on April 24 at 2:28 p.m. While it was only for a few seconds, the record demonstrated the possibility of a carbon-free power grid in the future.

The California ISO started producing the monthly Key Statistics – such as the most recent from January 2022 -- and the Annual Statistics in 2017 to gather vital stats about the power grid and market, including peaks and curtailments, historical data, and the Western Energy Imbalance Market benefits.

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