More and more alternative clean fuels are cropping up in microgrids to replace fossil fuel backup and boost resilience.
For example, instead of adding fossil fuels to solar and storage — a common backup strategy — Sesame Solar added green hydrogen to the company’s mobile nanogrids. This is hydrogen produced using renewable energy.
And renewable natural gas is becoming more common in microgrids.
Clean ammonia is the latest clean fuel that can be added to microgrids. Mainspring Energy recently completed successful testing of the use of clean ammonia and hydrogen in its “linear generator,” which is a new clean power technology that can utilize numerous fuels — including ammonia, hydrogen, biogas and natural gas — with the same hardware.
The generator’s ability to use ammonia and other fuels is good news for microgrids and the environment, said Michael Webber, the Josey Centennial Professor in Energy Resources at the University of Texas at Austin.
Fuel-agnostic microgrids
“Fuel-agnostic technologies are significant because they can work with a variety of low-carbon options, which gives consumers a lot of flexibility and helps us meet our net-zero goals economically. This flexibility will be valuable for microgrids whose fuel supply might vary from season to season or place to place,” Webber said.
The linear generator converts motion along a straight line into electricity using chemical or thermal energy. The generator can serve as backup, as a main generator or to help firm renewable energy resources, said Shannon Miller, CEO and co-founder of Mainspring Energy.
The generator can ramp production up and down to support solar and wind, serving as the “backbone,” she said. To support a solar and storage microgrid, for example, the generator could provide power when the sun isn’t shining or after the battery is depleted.
“What’s critical for customers is they can get backup and renewable energy firming,” she said.
Green ammonia comes from green hydrogen, which can be created with an electrolyzer powered by solar or wind that converts hydrogen to ammonia.
Starting more than a decade ago, Miller helped develop the technology as a student in Stanford University’s chemical engineering lab, and her team received initial funding from Bill Gates and Khosla Ventures.
The Stanford research team asked, “How do you improve power generation to ultimately get to zero carbon and think of cost and reliability at same time?” according to Miller. “The linear generator was the most promising path.”
And clean ammonia is a promising fuel. Green ammonia comes from green hydrogen, which can be created with an electrolyzer powered by solar or wind that converts hydrogen to ammonia. It can be stored easily and functions as a hydrogen-carrier fuel, she said. It can be piped and stored at low pressure in inexpensive tanks.
“Ammonia is having a moment now,” said Miller. “It’s used for fertilizer today, and there’s a massive industry to provide ammonia for fertilizer. Those technologies are at scale.”
Mainspring Energy utilizes green ammonia as a replacement for fossil fuels like diesel, she said.
To date, no customers are running their linear generators using ammonia, but that’s expected to change with Mainspring’s recently completed test of using clean ammonia and hydrogen in a linear generator. Currently, customers’ generators are running on biogas, natural gas and 30% hydrogen, said Miller.
Natural gas still less expensive
“They [linear generators] now can run on 100% ammonia. The goal is to eliminate natural gas. We allow customers to transition as fast as they can get the fuels,” she said. Right now, natural gas is still less expensive than ammonia. But many customers want to move to zero-carbon emissions and are investing in green fuels, which is expected to drive the costs down, Miller added.
In addition, the federal government is working to lower the costs of alternative fuels, she said.
The first Energy Earthshot — Hydrogen Shot — aims to reduce the cost of clean hydrogen by 80% to $1 per kilogram in one decade. Right now, clean hydrogen costs about $5 per kilogram, the DOE said.
The project has a goal of boosting the use of clean hydrogen by deploying it through the American Jobs Plan, which supports demonstration projects.
Meanwhile, Mainspring has been moving forward with a number of pilot projects, including one with Pacific Gas & Electric (PG&E). In 2021, the utility deployed a 240-kW Mainspring linear generator to offset diesel and support a microgrid during outages and public safety power shutoffs (PSPS) at its Angwin distribution microgrid site in Napa County. The generator used natural gas and biogas. The goal of the project was to see if the linear generator technology could be used to reduce the use of diesel generators during emergencies or PSPS.
Under an energy-as-a-service model, NextEra Energy Resources installed the linear generator in Angwin, California, a small town in Napa County.
The microgrid used a cogeneration unit at Pacific Union College and, coupled with diesel generation, provided power for a fire station, gas station, apartment building and a plaza.
PG&E tests linear generators
Paul Doherty, a spokesman for PG&E, said the utility used the generator during the 2021 wildfire season but “demobilized” it at the end of the year because the pilot ended.
PG&E also piloted an Aggreko YCube battery at its Foresthill, California, distribution microgrid, he said.
“These pilots were intended to advance the experience of PG&E and its vendor partners to develop workable, cost-effective solutions that accelerate the integration of nondiesel generation technology for PSPS mitigation and other wildfire safety-related outages,” Doherty said. The utility is exploring using similar technologies during the 2022 wildfire season, he said.
PG&E has been criticized for using diesel during PSPS and other outages and recently proposed using three kinds of microgrids to keep power flowing to customers when conventional electrical equipment becomes a wildfire threat.
Other pilots
Another customer piloting the linear generator technology is Lineage Logistics, a logistics solution provider that has 400 facilities across the world in 20 different countries. Last year, Mainspring deployed the first two linear generators for Lineage and announced in May that it is working on deploying up to 150 more units at Lineage sites.
While Lineage uses the power for its own resilience, the company could also use the generators to provide grid services, said Miller.
Linear generators with clean ammonia can play a role in helping companies meet their sustainability goals as well, something data centers are particularly interested in doing, according to Miller.
“These companies have set ambitious zero-carbon goals, and they don’t have a way to replace diesel backup. Ammonia is one way to do it,” she said.
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