California Utility Tests Linear Generator to Reduce Diesel Use at Napa County Microgrid

Share Button

Pacific Gas and Electric (PG&E) is deploying a 240-kW linear generator at a distribution system microgrid to see if the emerging technology can be used to reduce the use of diesel generators during emergencies or public safety power shutoffs (PSPS).


By Sundry Photography/

Using an energy-as-a-sevice model, NextEra Energy Resources installed the linear generator, developed by Mainspring Energy in Angwin, California, a small town in Napa County.

A linear generator directly converts motion along a straight line into electricity using chemical or thermal energy. Mainspring’s linear generator, with two moving parts, uses a low-temperature reaction of air and fuel to drive magnets through copper coils to produce electricity.

Set up in 2019, the microgrid uses a cogeneration unit at Pacific Union College and, coupled with diesel generation, provides power for a fire station, gas station, apartment building and a plaza.

The linear generator pilot project is part of PG&E’s efforts to use cleaner technologies during PSPS, planned power outages that aim to reduce the risk of wildfires.

“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.

Currently, PG&E uses mobile, diesel generators during emergencies and planned outages to provide power to customers. The generators are connected to the grid at substations, distribution microgrid sites, community resource centers and critical facilities.

In the Angwin pilot project, Mainspring’s linear generator will be paired with an on-site diesel generator to see if the hybrid solution can reduce diesel use and emissions during emergencies or PSPS events this year, according to PG&E.

The linear generator is connected to PG&E’s electric and natural gas distribution systems. 

NextEra Energy Resources, a NextEra Energy unit, is buying renewable biogas fuel to offset the linear generator’s natural gas use.

“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, NextEra Energy Resources vice president of distributed generation. “It’s important to get pilot projects into the field for real-world testing.”

NextEra, Mainspring partnership

In March, NextEra Energy Resources entered into a $150 million deal to buy and deploy Mainspring’s linear generators with an eye on markets like microgrids, commercial and industrial buildings, and utilities.

Mainspring’s technology can dynamically switch between natural gas and renewable fuels like biogas and hydrogen. With the ability to ramp generation up and down, Mainspring’s linear generator can serve fluctuating energy demand, help integrate intermittent wind and solar, and provide backup power if the grid goes down

Mainspring in May raised a $95 million Series D investment. The Menlo Park, California-based company’s investors include Bill Gates, AEP, ClearSky, KCK and Khosla Ventures.

Share Button


  1. Basically, the linear generator is an opposing piston 2-cycle engine that detonates all the fuel at the same time by compression similar to how a diesel chamber operates. It appears the fuel source is natural gas distribution line, though it could be powered by biofuels/methane in other installations. Generac does offer a 250kW propane generator, but I haven’t found an actual efficiency comparison to this Mainspring unit.