There’s something strange about where the clean energy transition has gotten stuck. Generating power from the sun and wind? Mostly figured out. Storing it? That’s the part nobody has fully solved. When the sun sets and the wind drops, whatever energy existed an hour ago is gone. A grid can’t run on what it can’t hold.

The answers getting serious investment right now are, to put it plainly, weird. One involves cooling air until it becomes liquid. Another involves heating industrial salt until it glows. Both are being built at scale. And both can do things that conventional lithium-ion batteries can’t.

The scale of the storage gap

The numbers around energy storage are moving fast. In the United Arab Emirates, a solar installation covering an area roughly the size of 12,600 football fields is being paired with 19GWh of battery storage, the largest battery scheme ever built. The project combines 5.2GW of solar capacity with enough stored power to run the equivalent of half a million homes through the night.

At the other end of the spectrum, researchers at the National Renewable Energy Laboratory in Colorado are building batteries small enough to fit inside electronic tracking tags for young salmon and eels barely three inches (about 7.5 centimeters) long. Different problem, same constraint: where does the energy go when you don’t need it yet?

Both push past lithium-ion, which has dominated storage for years. Lithium-ion works, but the materials behind it, cobalt, nickel, lithium, require extraction processes that have created real problems for ecosystems and mining communities. The batteries also wear out from repeated cycling. The alternatives coming online sidestep some of this. Several can run indefinitely and be recycled at end of life. The materials they rely on are, in almost any other context, completely unremarkable.

Air, cooled to -321°F (-196°C)

On the site of a former coal plant in Trafford, on the edge of Manchester, construction has started on a facility that stores electricity by freezing air.

Highview Power’s Carrington project uses surplus renewable power to cool air to -321°F (-196°C), squeezing it down to one seven-hundredth of its original volume as liquid. The liquid goes into insulated tanks. When the grid needs power, the liquid warms and re-expands into gas, spinning a turbine cleanly, without combustion. Once operational, the facility will deliver 300MWh of storage and 50MW of output for six hours, enough for nearly half a million homes. Andy Burnham, the former Greater Manchester mayor, called the project evidence that “this decade is the most exciting since the Victorian period” for the region.

Liquid air’s edge over lithium-ion is duration. Lithium-ion handles gaps of hours. Liquid air can sit for days or weeks, which matters if you’re trying to balance a grid through a stretch of overcast, windless weather.

Salt, heated to 1,040°F (560°C)

Nevada has been running a different version of the same experiment for the past decade.

The Crescent Dunes project uses 10,000 mirrors to focus sunlight on a central tower, heating a tank of potassium and sodium nitrate, the kind of industrial salts you’d find in a fertilizer plant, to 1,040°F (560°C). That heat holds for up to 10 hours after sunset. When power is needed, the heat drives a turbine. The energy sits in the salt until someone needs it.

Molten salt has an odd history. The same principle has long powered guided missiles and nuclear weapons, where superheated salt serves as a reserve energy source activated by the heat of launch. It’s a strange thing to have in common with climate technology. But it does suggest the approach is reliable: it has been trusted to work under extreme conditions for decades.

A different supply chain problem

One of the ongoing critiques of the clean energy transition is that it swaps one set of resource dependencies for another. Lithium for oil. Mining in one part of the world for drilling in another.

Molten salt and liquid air don’t fully resolve that. But they are built from materials that don’t require contested extraction. Molten salt uses nitrates found worldwide. Liquid air uses air. Both can be recycled at end of life. The supply chain looks a lot less fraught.

Energy storage has always been the part of the renewable transition that resisted easy answers. What’s strange is that the materials moving closest to solving it have been around forever. Nobody invented molten salt or liquid air. They just figured out, eventually, what to do with them.