A US utility planning to source most of its electricity from wind power is hoping that a novel 150-hour battery invented by a secretive start-up will ensure that the lights will stay on during extreme weather conditions.

Minnesota-based Great River Energy (GRE) —a not-for-profit wholesale electric power cooperative which provides electricity to about 700,000 homes and businesses — has announced plans to retire its 1.15GW coal plant and replace it with 1.1GW of new wind projects.

This will leave it with only one baseload power station, the 99MW Spiritwood combined heat and power plant, which runs off coal and natural gas, but will switch to run solely off natural gas. In addition, it has several gas peaker plants that act as back-up power.

The company says that the switch from coal to wind will reduce the cost of electricity to its customers — 28 member-owner distribution cooperatives — and that its “power supply resources will be more than 95% carbon dioxide-free, virtually eliminating carbon risk”.

As part of its announcement, GRE said it will build a 1MW/150MWh (150-hour) grid-connected demonstration storage project in Minnesota by the end of 2023 using novel battery technology from secretive Massachusetts-based start-up Form Energy. In other words, it can provide 1MW of output for 150 hours straight.

Form Energy has won $50m of funding from investors, including the Bill Gates-backed Breakthrough Energy Ventures, Italian oil company Eni and Macquarie Capital, but has revealed little about its technology — only that is an “aqueous air battery system” and is “ultra-low-cost”.

What is the technology behind the 150-hour battery?

It has been speculated that its technology uses sulphur as its main ingredient.

In an interview last year, Form’s chief scientist and co-founder, Yet-Ming Chiang, a professor of materials science at the prestigious Massachusetts Institute of Technology (MIT), said: “What we’re looking for are batteries that can use either metals or other elements that are much lower cost, and an example of that would be sulphur. In fact, one of the ironies is that fossil fuels, which we’re trying to get rid of, are one of the great sources of sulphur.”

Scientists at MIT developed a sulphur-air battery in 2017, which it said at the time would be 30 times cheaper than lithium-ion. Form Energy announced its first tranche of funding in the summer of 2018.

But Form Energy was the result of a merger between two start-ups working on similar technology — Chiang’s sulphur-based Baseload Renewables, and Verse Energy, a long-duration energy storage vehicle focused on a different combination of chemicals and run by former Tesla energy storage boss Mateo Jaramillo — now the CEO of Form.

According to one of its investors, MIT’s Engine, “the company hopes to settle on the best combination of chemicals and start large-scale prototypes to test on the grid within the next few years”.

How will the 150-hour battery be used?

GRE has said that “long-duration storage will help maintain grid reliability in the future during extreme conditions, such as a heat wave or polar vortex.

The utility’s vice-president, Jon Brekke, added: “Commercially viable long-duration storage could increase reliability by ensuring that the power generated by renewable energy is available at all hours to serve our membership. Such storage could be particularly important during extreme weather conditions that last several days. Long-duration storage also provides an excellent hedge against volatile energy prices.”

Form Energy believes that its 150-hour storage capability “allows for a fundamentally new reliability function to be provided to the grid from storage, one historically only available from thermal generation resources”.

Who are the battery's competitors?

But Form Energy’s battery is not the only technology that can provide that kind of long-duration energy storage. There are several competitors capable of scaling up their storage capacity to whatever size the customer would like, including:

  • Canadian company Zinc8's zinc-air battery, which will have three commercial pilot projects up and running by the end of 2022;
  • Highview Power’s liquid-air storage system, known as CRYObattery, which has already been commercialised;
  • Siemens Gamesa's ETES hot-rock thermal energy storage technology, now being tested in Hamburg;
  • Stiesdal Storage Technologies' GridScale hot-rock thermal storage, which is still at the pilot stage;
  • Google X spin-off Malta’s molten-salt system, also still at the pilot stage;
  • And of course, electricity can also be stored indefinitely by converting it to green hydrogen via electrolysis, and back to electricity at a later date using a fuel cell.

It remains to be seen which of these solutions will be the most reliable, efficient and cost-effective, but any of them will be able to eliminate the so-called “intermittency problem” of wind and solar power — and enable a future 100% renewable electricity supply.