California’s PG&E tapped 8,500 residential batteries for grid resilience

Peaking at nearly 32MW from 8,500 solar-plus-storage residential systems, Sunrun and Pacific Gas and Electric Company (PG&E) customer batteries provided consistent clean energy to California’s power grid through the summer and fall of 2023.

The virtual grid supply came courtesy of the partnership’s Energy Efficiency Summer Reliability Program, also known as Peak Power Rewards, a fully operationalised residential solar and storage distributed power plant.

The partnership between PG&E and Sunrun, a US-based provider of clean energy as a subscription service, saw a maximum enrolment of 8,500 customers and provided a consistent average of 27MW of power during evening peak hours for more than 90 consecutive days.

With an instantaneous peak output of nearly 32MW, the programme frequently supplied the grid with up to 30MW, which the partners say is sufficient power for more than 20,000 homes.

Sunrun managed the participating fleet of home batteries to provide power to PG&E in the same way that a centralised, traditional power plant would.

However, Peak Power Rewards was operational within six months of contract signature, a timeframe not possible when building traditional power plants, the companies state in a release.

“The Peak Power Rewards programme achieved a customer participation rate and power supply volume that’s never been accomplished before,” said Sunrun CEO Mary Powell.

“PG&E was able to confidently rely on the renewing daily resource of Sunrun’s fleet of home solar and storage systems. We are rapidly transitioning to a storage-first company and the results of this partnership highlight the unique capability that distributed power plants provide communities.”

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Software-managed consumption

Sunrun’s distributed power plant programmes use software to manage the discharging of thousands of home batteries onto the grid in coordination with utility needs, making it so customers don’t need to take any action.

Enrolled battery systems discharged energy back to the grid every day from 7pm to 9pm during the months of August through October, a critical window when energy needs are highest in California.

In exchange, customers received an upfront payment of $750 and a free smart thermostat for participating. Batteries enrolled in the programme retain enough energy to meet personal, essential needs in the event of a local power outage in their area.

“Working together with partners like Sunrun is a win-win-win for our customers, the electric grid and California as a whole. Solar-plus-storage plays a significant role in California’s clean energy future and we’re proud of our customers who are leading the charge with their clean energy adoption,” added Patti Poppe, CEO of PG&E Corporation.

PG&E has to date connected nearly 820,000 customers with rooftop solar to the electric grid, totalling approximately 8,039MW of capacity. Additionally, nearly 75,000 PG&E customers have installed and connected storage systems to the grid in PG&E’s service area, totalling more than 670MW of capacity.

According to the utility, these customers could on average rely on over 10 hours of backup power using their storage system, a critical resource for grid resilience, particularly during storms, heatwaves and emergency energy alerts.

“What is happening in California will soon need to be replicated across the country,” Powell said.

“Residential solar-plus-storage systems networked together as distributed power plants are answering the demand call by providing flexible, on-demand power stabilisation while also guarding against increasing rates.”