PG&E Deploys Mobile Power Generation Technology at Microgrid

Sept. 7, 2021
The utility partnered with the NextEra Energy Resources to install the Mainspring linear generator at the Napa County Microgrid.

Pacific Gas and Electric Company (PG&E) has deployed a "linear generator"—a new mobile power generation technology using natural gas and directed renewable biogas to displace existing diesel generation—at its Angwin distribution microgrid site in Napa County.

Working with a subsidiary of NextEra Energy Resources, LLC and Mainspring Energy, PG&E deployed the Mainspring linear generator as part of its commitment to integrate cleaner generation solutions for replacement power during emergencies like winter storms or earthquakes, and Public Safety Power Shutoff (PSPS) events.

Currently, PG&E strategically deploys mobile, diesel generators across its service area during emergencies and PSPS outages to rapidly re-energize thousands of customers. These generators are connected to the grid at substations, distribution microgrid sites, community resource centers, and critical facilities as needed and available.

The goal of the pilot is to demonstrate the performance of new, cleaner electricity generation technology at a PG&E distribution microgrid. The linear generator will be paired with the onsite diesel generator to ensure reliable service for the community of Angwin, and PG&E will study whether the hybrid solution can reduce diesel use and emissions during emergencies or PSPS events this year.

The pilot deployment follows a rigorous testing program by PG&E and Mainspring at the Mainspring facility in Menlo Park this spring, and months of collaboration between PG&E and Mainspring engineers.

"We know how important clean, reliable energy is to our customers and communities. We are excited to explore new technologies like the linear generator to help keep customers powered during larger outages while also reducing the use of diesel backup generation. This is a low-emissions, resilient, and affordable alternative that holds a lot of promise for our future," said Jason Glickman, Executive Vice President, Engineering, Planning & Strategy, PG&E.

A Creative Renewable Approach

NextEra Energy Resources subsidiaries provide PG&E with a diverse portfolio of nearly 1,000 MW of wind, solar and now linear generation. Under this agreement, NextEra Energy Resources provided the financing for the deployment of the linear generator, as part of its recently announced $150 million purchase and financing agreement with Mainspring.

 For the Angwin deployment, the linear generator is connected to both PG&E's electric distribution system and its natural gas distribution system. NextEra Energy Resources is purchasing biogas fuel that is renewably produced at another location. The procured biogas is processed and injected into the existing gas distribution infrastructure, offsetting the linear generator's usage of natural gas.

"NextEra Energy Resources sees strong potential for new technologies like the Mainspring linear generator to provide reliable, low-cost, and clean energy in California and elsewhere," said Matt Ulman, vice president of distributed generation for NextEra Energy Resources. "It's important to get pilot projects into the field for real-world testing, and we are pleased to enable innovative projects that offer resiliency to keep the lights on at businesses and homes."

Mainspring's Linear Generator

Mainspring's breakthrough technology, based on research originally conducted by the company's co-founders at Stanford University, is designed to meet grid demands by delivering dispatchable, fuel-flexible power that substantially reduces cost and carbon today, while accelerating the transition to the net-zero carbon grid.

One of the unique characteristics of the 240-kW Mainspring linear generator is that it can ramp up and down quickly to meet power load demands at a fraction of the emissions of reciprocating engine technologies.

"Extreme weather events and the rise of electrification are driving increasing demands on the electric grid for resiliency at affordable costs. At the same time, we need to be moving rapidly toward a net-zero-carbon grid," said Mainspring CEO Shannon Miller. "Mainspring designed our platform to meet this challenge, and we're proud that our product is now deployed to help PG&E and its customers to address these challenges and provide them with a cleaner, resilient, and affordable source of power." 

A linear generator—distinct from an engine, microturbine, or fuel cell—is a device that directly converts motion along a straight line into electricity using chemical or thermal energy. The design of Mainspring's linear generator uses a low-temperature reaction of air and fuel to drive magnets through copper coils to efficiently produce electricity. This innovative design, combined with the company's proprietary adaptive control software, enables high efficiency, near-zero NOx emissions, full dispatchability, and seamless switching between fuels.

The product achieves low capital and maintenance costs through use of standard materials, only two moving parts, and an innovative air bearing system that eliminates the need for oil. It operates without the use of complex mechanical systems or expensive catalysts.