Mateo Jaramillo, the co-founder of Form Energy, is taking an unconventional approach to storing renewable energy. Lithium-ion batteries are all the rage today—we use them in computers, cell phones, and electric vehicles (EVs), as well as to help bank energy from renewables like wind and solar when power is abundant and then supply them to the grid when the sun isn’t shining or the wind isn’t blowing. The problem, though, is that lithium supplies are likely to get tight in the next couple decades as new battery production scales up faster than mining can keep up—not to mention that there’s a host of environmental concerns around mining lithium in the first place. And while lithium batteries are good at covering for renewables for a few hours or overnight, they’re not great at keeping power flowing for periods longer than that, like a stretch of three or four cloudy, windless days. Form Energy’s batteries are meant to solve both those issues. Instead of lithium, the massive batteries they’re building use the most common elements on earth: iron.

Form’s batteries can only put out a little energy at a time, so they have to be big and heavy to get a decent amount of power out of them. That means that you could never run an EV with one—to put out the same amount of power as a lithium-ion battery, Form’s battery would have to be about 100 times heavier. But they store a lot of energy, meaning that you could keep pulling power out of them for hundreds of hours. And, just as importantly, they’re cheap. All that has got a lot of people in the renewable energy space excited—the company is already developing two projects. A pilot facility in Minnesota will store enough energy to power about 400 homes for several days. Another facility, in Georgia, could end up being 10 times as large. TIME sat down with Jaramillo to talk about Form’s technology and what they’re planning next. The following conversation has been edited for length and clarity.

TIME: Can you explain how Form’s technology works compared to conventional lithium-ion batteries?

Jaramillo: Quite simply, we are reversibly rusting iron. You start with metallic iron, and you rust it, and then you drive it back in the other direction and return to the metallic state. That’s the fundamentals of it. Lithium-ion [chemistry] is incredibly energy dense both in terms of weight and volume, so that means you can move it around. You can put it in your pocket in a phone, or you can put it in a car and drive it around. However, because of that, it is relatively expensive. The problem that we’re trying to solve is this multi-day energy storage problem, and what you care about most is cost. We don’t care so much about how much it weighs, or how much space it takes up. That’s why we have selected an entirely different chemistry.

What’s the promise of this technology?

I always like to put the technology in the context of the problem we’re trying to solve—it is the problem of decarbonizing the electric grid. There’s three angles to that: it needs to be cost effective, you need a reliable grid, and it’s got to be decarbonized. It’s this triple challenge, and what having cost-effective, multi-day storage does is it makes all of that easier. If you don’t have this kind of technology or something like it, what you end up with is a grid that you either pay a lot more for, or you keep costs where they are but it’s much less reliable. Or you have low cost and it’s reliable, but you don’t have it decarbonized. So it allows you to tie those three goals together and deliver on them in a relevant timeframe.

Where in the development stage are the batteries?

We are racing as fast as we possibly can, to be clear. We have those two announced projects [in Georgia and Minnesota] but more are coming very shortly. We are actively signing contracts for delivery starting in a couple of years. We’ll announce our manufacturing location relatively shortly as well. That will provide a lot more detail and context for exactly how we’re going to be scaling up and the timeframe that we’re going to be doing it in. But it is as immediate as we possibly can make it, and our customers are asking us to go even faster than what we had originally been contemplating.

Has that build out been affected by the passage of the Inflation Reduction Act this year?

Certainly it has. So the IRA [Inflation Reduction Act] passed in August, and since August the entire industry has been digesting the scope and scale of that bill, which is massive. It benefits us in a couple of ways, both direct and indirect.

The indirect ways may be the most impactful, because it is essentially industrial climate policy—it’s saying the U.S. is going to be doing these things at a massive scale, and the tax incentives really unlock massive amounts of capital to come into the electricity utility sector. All of our customers are accelerating all of their plans. When you have higher and higher penetrations of renewables, the need and the value for what we are doing goes up. We’re going to be hitting the renewable targets sooner than expected. [That means] the technology that Form is working on becomes relevant, much sooner, at a much larger scale. It’s a massive rising tide that’s lifting many boats.

And then directly, there are things like the investment tax credit for energy storage specifically which previously had not been the case.

So what’s the niche that Form fills, in contrast to other energy storage options?

Wind and solar are fundamentally weather-driven power resources, and the weather as we all know is intermittent. They’re intermittent on an hourly basis, and there are technologies out there today that address sort of that time period of intermittency. Increasingly, lithium-ion has been deployed to do exactly that. But it’s still really only cost-effective over that 10-hour range. It is too expensive to cover multi-day periods of intermittency. That period is what Form is targeting. We have a 100-hour rated duration battery—minimum four days but longer in some cases. Today, [that range] is essentially covered by coal and natural gas.

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Write to Alejandro de la Garza at [email protected].

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