New renewables records – what they mean for the grid and its carbon-free future

By Amber Motley, Director, Short Term Forecasting |

The California Independent System Operator (ISO) has seen continued growth of clean energy this spring, including record-setting solar generation and battery output. It marks the fifth consecutive year that solar has hit new peaks within the ISO footprint, while battery storage has become a major resource for grid reliability in just the last few years.

Spring is often when records get set for renewable energy performance in the ISO because of the combination of mild weather and plentiful sunshine for solar generation. Days when renewables supply up to 100% of the state’s energy needs during some hours have become more common in recent years.

It’s important to keep these records in perspective and not to overstate their significance. There’s still a long way to go to reach the state’s much larger goal of having a 100% carbon-free grid by 2045, but this spring’s advances are significant steps in that direction.

The latest gains are outlined in the ISO’s April Renewables Performance Report, and I want to thank Lysha Matsunobu, an ISO Power Systems Forecaster Specialist, and Hudson Sangree, our Lead Technical Writer in Market Strategy and Governance, for all their help in compiling this data and helping me describe its meaning in this blog post.

In April 2024, the ISO set a record of serving 117% of total system demand with renewables in one five-minute interval, compared to 103.5% in April 2023 and a previous record of 107% in June 2023. The average total system demand served by renewables across all five-minute intervals in April 2024 was 49%, compared with 43% last April.

The percentage of consumer demand served by renewables is a new addition to the ISO’s monthly performance reports.

The percentage of consumer demand served by renewables is a new addition to the ISO’s monthly performance reports. Consumer demand is measured by taking total system demand and subtracting energy resources that participate in the ISO’s market and draw power from the grid, such as batteries when they are charging and hydropower plants that pump and store water for later use. That leaves demand from homes, businesses and non-participating resources, including some batteries and hydro.

This year, there were 70 days from March 1 to May 31 when renewables — including solar, wind and smaller hydropower plants — served 100% of consumer demand for parts of each day. During 54 of those days, solar and wind alone at times served 100% of consumer demand.

At one point, the ISO had enough renewables on the system to meet 150% of the electricity needs for consumer demand, including the homes and businesses in its territory.

Wind hills sun

At one point, the ISO had enough renewables on the system to meet 150% of the electricity needs for consumer demand, including the homes and businesses in its territory.

Solar and battery capacity have continued to increase from year-to-year, reaching new highs this spring and playing a key role in the state’s efforts to reach 100% clean energy over the next two decades, as required by California Senate Bill 100, signed into law in 2018.

Utility-scale battery storage briefly supplied a record 7,000 megawatts (MW) of electricity to the grid on April 30. (A megawatt provides roughly enough electricity to meet the instantaneous demand of 750 homes at once.) This record was broken a week later on May 7 when batteries supplied 7,200 MW, then again on May 16 with 7,500 MW.

As of May 31, the ISO has 9,163 MW of installed grid-scale battery capacity, more than doubling the 4,515 MW of battery capacity it had at the same time last year. 

Batteries within the California ISO footprint have increased from negligible amounts in 2020 to the equivalent of more than four plants the size of the Diablo Canyon nuclear power plant, the state’s largest generating facility.

Batteries are a key reliability resource for the ISO because they can store the ample solar power produced in daylight hours for use on hot evenings, after the sun sets but electricity demand remains high for air conditioning. The state’s most challenging periods in the past three years have occurred during hot summer evenings.

Unlike traditional power plants, most batteries can supply only about four hours of energy when fully charged. That means it’s important to optimize the use of battery resources for when they’re needed most, especially during evening peak demand. We continue to refine our market rules to ensure that batteries are dispatched in line with the reliability needs of the grid.

In April, solar generation reached an all-time high of 18,374 MW. That record was surpassed on May 13, when solar generation peaked at 18,933 MW.

Peak output from solar arrays has climbed steadily since last decade, with sizeable additions year-over-year becoming the norm. For instance, this spring’s record (so far) bested last May’s peak of 15,106 MW by 3,268 megawatts, a nearly 22% increase.

California’s clean energy and storage additions are impressive, but there is still much to be done to meet the state’s 100% clean energy mandate.

The California Public Utilities Commission’s latest integrated resource plan calls for an additional 56,000 MW of new clean generation by 2035 to meet grid reliability and state greenhouse gas reduction goals. This means we will continue to sustain an accelerated pace of new resource development and onboarding for years to come.

While more work remains, the frequent record-setting occurrences during spring in California illustrate the state’s progress in moving away from fossil fuels and show that grid operators at the ISO continue to manage growing amounts of renewable resources on the grid reliably and efficiently. 

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