Most batteries run at 25°C. We’re testing ours at 250°C. Here’s why

The duck curve is the problem that all of us working in sustainable energy are trying to solve: that bendy line that represents the demand peaks that hit in the morning and evening each day.

How can we make sure there’s green energy there for people making their morning coffees and cooling their homes?

Solar, wind, and other renewable solutions, by their nature, don’t produce power at all hours — so storage becomes more important, allowing us to fill out those surging peaks with energy saved up throughout the daytime dips.

The logic is simple enough. But to date, the big barrier to meeting the challenge has been cost.

Even with the price of Russian gas sky-rocketing — or the taps being turned off entirely and everyone else putting up their prices in opportunistic response — the costs associated with energy storage have proven to be too high.

Central to this cost challenge is not just materials, but the price of keeping things cool.

The cost of keeping things cool

Anything that’s expensive to produce, needs to deliver decent efficiency once it’s up and running. For batteries, the measure for this is round-trip efficiency, or RTE.

In simple terms, RTE is the measure of how much energy you get out of a battery versus how much you put in initially.

One of the reasons lithium-ion batteries have proven so popular over the years is their high RTE: a fresh lithium-ion unit will give you back around 85-90% of what you put in each time.

However, to do this, the battery needs to be kept at a temperature of around 25°C. Anything over and performance, safety, and lifespan all take a hit.

Charging and discharging energy generates its own heat, of course, so complex —and expensive — cooling systems are used to keep things steady.

Here in England, that 25°C limit is less troublesome. But in countries like India — which are among the places that will most benefit from future energy solutions, and where daily temperatures have risen beyond 50°C — the cost conundrum is only going to get greater.

In these sweltering climates, batteries are circulated with refrigerated liquid coolant, encased in shipping containers, and stored in warehouses with air con units pumping at all hours. All at a cost.

But even with all these measures in place, overheating failures are still a common occurrence. The risk of fires and thermal runaway — another quirk of lithium-ion units, which makes them virtually impossible to extinguish — only exacerbates the challenge.

It’s not working. So we need to start thinking outside of the status quo, not only about what materials we’re using to make our batteries, but how we can bring down operational expenditure too.

If storing and cycling energy is going to generate lots of heat, and keeping that temperature down is going to cost lots of money, then why haven’t we considered ways to use the excess heat to our advantage?

We started with this question, and ended up running our batteries not at 25°C, but at 250°C.

Let me explain why.

Why we’re running our batteries at 250°C

For most people, 250°C is the temperature you need to cook a pizza at home.

And while it might sound counterintuitive, the science tells us it’s ideal for running batteries too.

Our results show that operational costs are far lower when you remove the need to keep cells cool, and that performance actually improves.

We placed our battery units in a vacuum-seal casing (like a giant Thermos flask) and found that once we’d expended a bit more energy getting each unit up to its pizza-baking temperature, the system would effectively run itself — consistently, and with minimal leakage. Round-trip efficiency measured at 94% and above.

The tests ran on 10kWH units, which is roughly what you need to power a home. But the real reason we tested at this scale wasn’t to simulate household conditions. The science of surface area and cooling means that as our units get bigger for commercial and industrial customers, it’ll be even easier to maintain a steady operating temperature with our passive cooling systems. We tested at a smaller scale in order to push our hypothesis to its toughest limits.

We believe the true potential of our technology is global — Gigafactory scale — serving rooftop solar, data-centres and the grid, and filling out that duck curve with renewable energy.

These tests, making use of cheap, abundant materials, and an innovative take on temperature management, marks a first, significant step towards achieving that.

And who knows, with all this expertise, we might make a pizza oven for LiNa HQ too…