Lumenhalt's Salt Battery Faces Its First Real-World Test

Port Calder — For four years, Lumenhalt has made its case in slide decks and lab reports: a battery built from sodium, iron and ordinary table-salt chemistry that, the company says, costs about a third less than a lithium-ion pack of the same size and cannot catch fire. Next month, that case moves out of the lab and onto a windswept pier.

The Port Authority announced on Monday that two of the company's container-sized units, with a combined capacity of 4.8 megawatt-hours, will power the Gull Island ferry terminal through the winter, charging overnight from the grid and from a small rooftop solar array, then carrying the terminal through the morning and evening peaks when electricity is most expensive.

It is a modest deployment by industry standards. But for Lumenhalt, a 140-person company that operates out of a converted rope works on Foundry Quay, it is the first time its cells will run outside a controlled test facility, in salt air, through freezing nights, for a customer that cannot afford to have the lights go out.

Cheaper, heavier, safer

Sodium-based batteries are not new. Their appeal is that sodium is abundant and inexpensive, while lithium supply chains are long and volatile. Their drawback has long been weight: sodium cells store less energy per kilogram, which makes them a poor fit for cars and phones.

Lumenhalt's founders argue that weight barely matters for batteries that sit on the ground. "Nobody is trying to drive a ferry terminal anywhere," said Sunniva Okafor-Lind, the company's co-founder and chief executive, in an interview at the rope works, where a row of prototype cells hummed under a tarpaulin. "What a building or a substation cares about is cost, lifespan and whether it is going to burn down. On all three, we think we win."

The company says its cells have survived 9,000 full charge cycles in testing with less than 15 percent loss of capacity, which would translate into roughly 20 years of daily use. Those figures have not been independently verified, and Lumenhalt has declined to publish its full test data, citing pending patents.

"Nobody is trying to drive a ferry terminal anywhere."Sunniva Okafor-Lind, Lumenhalt

The skeptics

That reticence worries some outside experts. Dr. Pieter Halloran, who studies grid storage at Marrow Valley Polytechnic and has no ties to the company, said the winter pilot would be "the first honest number we get."

"Lab cycles are lab cycles," Dr. Halloran said. "Batteries behave differently when it is minus five at four in the morning and the ferry is late and everyone turns the heaters on at once. If these cells hold up through February, that tells you more than any spreadsheet."

He also noted that several sodium-battery start-ups elsewhere have struggled to move from pilot projects to factory-scale production, where small defects multiply across millions of cells.

Jobs on the quay

Local officials have their own reasons to hope the test goes well. Lumenhalt has said that if the pilot succeeds and it closes a planned funding round, it intends to build a cell factory on a former shipyard parcel at the south end of Foundry Quay, employing up to 600 people.

The Port Authority's executive director, Calvin Desrosiers, said the agency had kept its diesel generators on site as a precaution but expected not to need them. "We would not have signed this if we thought we were gambling with the ferry," he said. "We think we're being early, which is different."

Ms. Okafor-Lind said the company would publish monthly performance figures from the terminal, a first for the start-up. "If it works, everyone will see it work," she said. "And if something goes wrong, everyone will see that too. That's the deal."