The hydrogen challenge – How to sell a generator no one has heard of

The hydrogen challenge
Hydrogen, the most abundant chemical element in our world, emits no planet-warming gasses when burned, presenting a tantalizing solution for hard-to-abate sectors like shipping.
The trouble is, producing hydrogen isn’t always climate friendly — especially if it’s done through methods involving fossil fuels. That’s why the world needs “green hydrogen,” which is made by splitting water using industrial-scale electrolyzers in a process powered by renewable energy.
Despite its potential, hydrogen has played a small role in the energy transition so far. That’s because it’s still relatively expensive to make, store and transport. Also, most machines and industries aren’t adapted to use it. With major subsidies for hydrogen set to kick in from the US climate bill, all that could change.
This year, BNEF awarded three startups working to make green hydrogen mainstream. In today’s newsletter we’re focusing on one of those BNEF climate tech Pioneers: a company that’s created a novel generator than can run on hydrogen. You can read about the other winners here.   

How to sell a generator no one has heard of
By David R. Baker Click here to read the full version of this story on

Two generators thrumming in a cramped Silicon Valley parking lot represent a clean power technology so new that most potential customers don’t know it exists. For Adam Simpson and his startup, Mainspring Energy Inc., that’s both a curse and an opportunity.
Inside the generators, steel cylinders wrapped with magnets race back and forth through copper coils 12 times per second, generating electricity. There’s fuel involved, but no combustion: Nothing burns. The generators’ fast, muffled drumming—about as loud as traffic on the Bayfront Expressway a few yards away—makes them sound like engines, but they aren’t.

Mainspring calls them linear generators, and as the company’s chief product officer and co-founder, Simpson often finds himself explaining them to the world. Most of the technologies powering the clean energy transition—the solar cells, wind turbines, batteries and fuel cells—have been commercially available in one form or another for decades, even if they’re only now taking off. Businesses understand them and have grown comfortable slapping them on rooftops or planting them next to offices. Not so with the linear generator, which Mainspring started deploying in 2020. As far as the company and its backers can tell, no one else sells one.
Adam Simpson, CPO & Founder, Matt Svrcek, CTO & Founder and Shannon Miller, CEO & Founder standing with a linear generator core at Mainspring Energy’s manufacturing facility in Menlo Park, California. Photographer: Spencer Lowell for Bloomberg Green

“There’s a lot of education we need to do,” says Simpson, who also leads Mainspring’s government affairs team. “It’s a brand-new category of generation that customers and grid planners didn’t know about, a tool they didn’t know they had.” To help them grasp it, Simpson sometimes takes policymakers through the company’s small assembly plant in Menlo Park, where units awaiting shipment to customers are tested in the parking lot. “It’s real,” he says. “They can come touch it.”

Mainspring has managed to persuade some big names in the energy world to give its generators a chance. The world’s largest producer of renewable power, NextEra Energy Resources LLC, signed a $150 million agreement in 2021 to buy and deploy the generators as well as finance purchases for other customers. 

The basic idea of the linear generator stretches back 80 years. But for much of that time, it was considered a potential design for a combustion engine in cars. Mainspring took a very different approach.

Each generator core consists of two cylinders, called oscillators or translators, that move in opposite directions—like a two-pronged pogo stick lying on its side. As they swing inward, they compress a mix of fuel and air until the fuel molecules break down and push the oscillators outward. Air springs catch them and send the oscillators racing toward each other again. Although they’re housed in a casing, the oscillators glide on a thin cushion of air to minimize friction. Magnets on the cylinders pass back and forth through copper coils to generate electricity. Mainspring packages two of the 20-foot-long cores side by side within a modified shipping container to create each generator, which can produce 230 kilowatts of electricity. That’s enough for a typical retail store, according to the company.

For now, the generators’ fuel is natural gas, biogas (which landfills or dairy farms can produce) or a blend of gas with hydrogen. But the units that ship next year will be able to run on any of those fuels, as well as ammonia, and switching fuels won’t require a hardware upgrade.

To date, the company has raised more than $500 million from investors that include Shell Ventures, utility American Electric Power Co. and Bill Gates.

Along with NextEra, other big name customers include Cold food storage specialists Lineage Logistics LLC decided to try a linear generator at a warehouse in the Southern California city of Colton, matching it with a rooftop solar array. Now the company has generators installed at three sites and is actively planning 15 more. The novel technology is working, says Jesse Tootell, Lineage’s senior manager for energy analytics.

“We haven’t had a single month when they’ve missed a single spec,” he says. “They’ve delivered on every technical dimension we care about.”