Ammonia joins hydrogen and biogas as a clean fuel in microgrids and ‘linear generators’

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.