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PG&E and NextEra Energy Resources pilot Mainspring linear generator

In the United States (US), combined natural gas and electric utility Pacific Gas and Electric Company (PG&E) a subsidiary of PG&E Corporation that services central California (CA), has announced the deployment of a "linear generator"—a new mobile power generation technology utilizing natural gas and directed renewable natural gas (RNG) to displace existing diesel generation—at its Angwin distribution microgrid site in Napa County.

The Mainspring Linear Generator – distinct from an engine, microturbine, or fuel cell – directly converts motion along a straight line into electricity using chemical energy. At the heart is a 120 kW linear generator core. The first product features two cores in each package, working in tandem. Made out of standard materials with only two moving parts and operates without the use of oil, fuel cell catalysts, or complex engine mechanical systems. Shipped in a standard 20 ft container with combined grid-tie inverters and auxiliaries into turn-key packages for fast and simple installation, this leads to low capital and maintenance costs (image courtesy Mainstream Energy).

PG&E is working with a subsidiary of NextEra Energy Resources, LLC, one of the largest wholesale generators of electric power in the United States that together with its affiliated entities is one of the world’s largest renewable power generators from wind and solar, and technology developer Mainspring Energy Inc (Mainspring).

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.

Demonstrate hybrid solution to reduce emissions

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 generators. This is a low-emissions, resilient, and affordable alternative that holds a lot of promise for our future, said Jason Glickman, EVP, Engineering, Planning & Strategy, PG&E.

Creative renewable approach

NextEra Energy Resources subsidiaries provide PG&E with a diverse portfolio of nearly 1 GW 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 US$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 RNG that is renewably produced at another location.

The procured biomethane 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. 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, said Matt Ulman, VP of distributed generation for NextEra Energy Resources.

Mainspring’s novel 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. 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, said Shannon Miller, CEO of Mainspring.

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, fully dispatchable, and seamless switching between fuels.

The product achieves low capital and maintenance costs through the 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.

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