A first-of-its-kind partnership between California’s largest utility and a US provider of clean energy as a subscription service helped strengthen the state’s energy grid with home solar-plus-storage systems.

Peaking at nearly 32MW from 8500 solar-plus-storage residential systems, Sunrun and Pacific Gas & Electric (PG&E) provided consistent, reliable clean energy to California’s power grid through the summer and autumn of 2023.

The energy efficiency summer reliability programme, also known as Peak Power Rewards (www.sunrun.com/peak-power-rewards), is a operationalised residential solar and storage distributed power plant. The programme quickly achieved its maximum enrolment of 8500 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, sufficient power for more than 20,000 homes.

California-based Sunrun managed the participating fleet of home batteries to provide power to PG&E in the same way 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 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.”

Sunrun’s distributed power plant programmes use software to manage the discharging of thousands of home batteries seamlessly onto the grid in coordination with utility needs, making it so customers don’t need to take any action. Peak Power Rewards created a favourable situation for PG&E, Sunrun and their shared customers. Enrolled battery systems discharged energy back to the grid every day from 7pm to 9pm from August to 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,” said Patti Poppe, CEO of PG&E. “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. Every day, we’re looking at new and better ways to deliver for our hometowns while ensuring safety, reliability and resiliency for our customers.”

PG&E says it is the USA’s utility leader in both rooftop solar and behind-the-meter storage, having connected nearly 820,000 customers with rooftop solar to the electric grid totalling approximately 8039MW of capacity and with nearly 75,000 customers having installed and connected storage systems to the grid in PG&E’s service area, totalling more than 670MW of capacity. These customers could on average rely on over ten hours of backup power using their storage system, a critical resource for grid resiliency, 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.”

Sunrun (www.sunrun.com) provides distributed power plant programmes and has years of experience managing a fleet of tens of thousands of home batteries and assisting utilities with demand response planning. Unlike traditional power plants, Sunrun’s virtual power plants can quickly be set up and operationalised without the need for costly new infrastructure, as was the case with the PG&E partnership. Sunrun and PG&E are exploring possibilities for future programmes that will jointly benefit customers and electric grid resiliency.

PG&E (pge.com) is a combined natural gas and electric utility serving more than sixteen million people across northern and central California.