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Clean energy journalism for a cooler tomorrow

These generators can switch from running on fossil fuels to clean fuels

Mainspring Energy’s flexible-fuel” on-site generators could make it much easier for customers to clean up their act as hydrogen and ammonia fuels become increasingly available.
By Jeff St. John

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A Mainspring Energy linear generator
This linear generator from Mainspring Energy is designed to be able to run on a variety of fuels, including zero-carbon hydrogen and ammonia. (Mainspring Energy)

Mainspring Energy says its generators can do something other generators can’t — run on zero-carbon fuels as easily as they do on fossil fuels.

On Wednesday, the Menlo Park, California–based startup announced that its generators have passed tests running at high efficiency on 100 percent hydrogen and 100 percent ammonia fuels. And unlike typical on-site power generators, Mainspring’s don’t need fundamental alterations to be capable of fuel-switching.

Mainspring’s linear generators are fundamentally different from the reciprocating engines, microturbines and fuel cells that usually serve as on-site generators. They capture the energy of two oscillators driven back and forth by the energetic reaction of fuel and air in a central chamber, and use software and power electronics to control the position of those oscillators really precisely and change them on the fly,” CEO Shannon Miller said in an interview. We can adjust to those different fuels without having to change the hardware out.”

This kind of fuel-flexible capability is something of a holy grail for generator makers seeking to serve the needs of a low-carbon future. Major engine and generator makers such as Cummins and Wärtsilä are hard at work on products that can run on hydrogen and ammonia in various blends, and General Electric, Mitsubishi and Siemens are among the turbine makers working on versions that can run on blends with increasingly higher proportions of hydrogen.

But reciprocating engines and turbines need to be engineered for use with specific fuels or fuel mixes to achieve safe and high-efficiency operation. None have yet been built with the purpose of switching regularly between different low- or zero-carbon fuels using the same hardware, Miller said.

That distinction could set Mainspring’s product apart as a device that can be installed to run on fossil gas today, and then switch to increasing blends of hydrogen or ammonia in the future without having to be replaced, she said.

Customers don’t know which fuels are going to be available when,” Miller said. They don’t want to buy a system and then encounter some regulatory or cost change they didn’t anticipate.” This system allows them to shift to fuels based on what’s available and low-carbon.

A Mainspring Generator in its enclosure at a customer site, a large gray metal box
A Mainspring generator in its enclosure at a customer site. (Mainspring Energy)

Mainspring has installed its generators with customers including Kroger, Pacific Gas & Electric and Florida Power & Light. Last year it inked a $150 million contract with NextEra Energy, the U.S. utility and renewables developer that owns Florida Power & Light, which is installing Mainspring generators at sites across the U.S.

Mainspring raised $150 million last month, bringing its total funding to date to more than $375 million. Investors include Lightrock, Khosla Ventures, Bill Gates, Fine Structure Ventures, Princeville Capital and Lineage Ventures. The latter investor is the venture arm of Lineage Logistics, the global cold-storage logistics provider that agreed last month to deploy up to 150 of Mainspring’s 250-kilowatt generators in the U.S., as well as explore the use of carbon-free fuels to power them.

The value of flexible backup power in a cleaner grid

The backup generator market has grown significantly over the past few years as extreme weather has driven more power outages and grid instability. Generator providers such as Aggreko, Cummins, Generac and Wärtsilä have been expanding their business, as have microgrid developers like Enchanted Rock and Scale Microgrid Solutions and fuel-cell manufacturers including Bloom Energy and FuelCell Energy.

But today’s diesel and fossil-gas-fueled generators emit a range of pollutants that could violate local air-quality mandates and undermine state clean energy goals. Even fuel cells, which convert fuels to electricity without combustion, still emit carbon dioxide when they run on fossil gas rather than hydrogen.

This tension between keeping the lights on and reducing emissions has come to a head in California, where aggressive decarbonization goals are running up against rising threats to grid reliability. Over the past several years, power outages triggered by wildfires and heat waves have led to a big increase in backup-generator installations in the Golden State. Last month, Governor Gavin Newsom (D) proposed spending $5.2 billion over the next four years on emergency reliability resources, most likely fossil-fueled power plants and generators.

But backup generators can also play a role in bolstering cleaner energy resources on the grid, particularly if they can run at times when the grid is operating normally. A number of sites are using generators to provide stability to solar- and battery-powered microgrids or to help reduce the grid stresses brought on by the power demand of electric-vehicle chargers, for example.

How often backup generators can be used in nonemergency situations depends on whether the pollutants they emit violate regional or state air-quality rules. California has some of the country’s strictest rules on this front, although they’ve been relaxed during times of grid emergencies.

That’s why Lineage Logistics chose Mainspring’s generators to provide 480 kilowatts of power alongside a 3.3-megawatt solar array it installed at its Colton, California facility last year. Colton is within the South Coast Air Quality Management District, which has strict limits on local generator emissions.

Lineage Logistics facility in Colton, Calif.
This cold storage facility in California is using solar panels and generators from startup Mainspring Energy that can switch between fossil gas and zero-carbon ammonia and hydrogen. (Lineage Logistics)

Lineage’s solar-and-generator system in Colton generates enough power to cover all of the facility’s electricity demand on an annual basis. It’s one of a number of distributed energy projects the company is pursuing as part of its commitment to achieving net-zero carbon emissions by 2040.

One of the most interesting things about Mainspring’s generator is that it doesn’t light the fuel on fire,” said Jesse Tootell, Lineage’s senior manager of analytics. 

Instead, Mainspring’s devices compress a mix of fuel and air to a point where it undergoes low-temperature combustion,” he said. That chemical reaction yields almost none of the compounds such as sulfur oxides or nitrogen oxides that contribute to respiratory illnesses or smog formation, which means we can run that thing almost 24/7.”

This has allowed Lineage to keep its 480 kilowatts of Mainspring generators available to run on a nearly constant basis since the Colton system went online late last year, Tootell said. It’s used that power to balance the ups and downs of solar generation that can come when clouds pass overhead, as well as to balance the costs of electricity from the grid.

Mainspring’s systems also run efficiently at power output ranges from close to zero up to 100 percent, unlike many types of generators and fuel cells that operate much less efficiently when they’re not running at full capacity, he said. All of these features are expected to allow Lineage to pay back the costs of its Mainspring generators within just a few years of operation, he said — the kind of rapid payback that can’t be achieved with backup generators that are only fired up during emergencies.

Going from fossil gas to zero-carbon fuels 

Shifting to running the generators on lower-carbon fuels will be another step toward meeting Lineage’s zero-carbon goals. While the company hasn’t made any specific commitments yet, we’re very excited about the potential of alternative fuels,” Tootell said.

Those could include biofuels produced by waste digesters, he said. Such biofuels still emit carbon when used to power generators, but those emissions are theoretically balanced out by the reduction in carbon or methane emissions that would have otherwise come from the organic waste feedstock.

Lineage is also exploring the use of hydrogen and ammonia, neither of which contain carbon, Tootell said. Just how and when these fuels might become available at prices and volumes that would allow them to be used as an economically viable source of local electricity generation is an open question. Today, sourcing hydrogen and ammonia as a replacement for fossil gas delivered via utility pipelines is cost-prohibitive, as are the technology options for generating these fuels locally.

But Europe, where government mandates are supporting enormous investments in facilities to convert renewable electricity to hydrogen, is where Lineage might expect to first find opportunities to use that fuel, he said.

Ammonia, a compound of nitrogen and hydrogen that’s produced at massive scale for use in production of fertilizer and other chemicals, has been targeted by a number of industries as a potential carbon-free fuel. Cargo ships are a particular focus for ammonia, which can be stored and shipped more easily than liquid hydrogen.

Ammonia is also used in industrial-scale refrigeration systems like those Lineage has at most of its sites, Tootell noted. We already have the ability to procure and store ammonia,” he said.

Whether that stored ammonia could be cost-effectively used as a fuel would depend on a number of factors, he said. But in simple terms, if it’s cheaper than the price of power from the grid, that’s what we can do.”

Mainspring’s technology can convert ammonia to energy without requiring mixture with other fuels that have lower ignition temperatures, as is required for combustion engines using the fuel, Mainspring’s Miller said. Ammonia-fueled generators do need an additional catalyst to reduce smog-forming nitrogen oxide emissions, but that’s a relatively simple add-on, she said.

While none of Mainspring’s customers have yet made the switch to hydrogen or ammonia to fuel their linear generators, there are some customers who really want to start right off on hydrogen and ammonia,” she said. They’re customers that are sort of taking the supply chain more into their own hands.”

Tootell said that most large commercial and industrial sites haven’t yet explored the potential for using zero-carbon fuels for on-site power. In the case of Lineage, which needs backup generators to ensure its refrigerators keep running during grid outages, that’s largely because we’ve never owned an asset before Mainspring that was even remotely able to use another fuel besides diesel and natural gas,” he said.

It’s hard to quantify how valuable it will be to have generators that can switch fuels with a software upgrade, he said. But it’s not hard to say how interesting that is.”

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.