Rust? The trains? Why clean energy turns to exotic ideas to solve its storage problem

Mateo Jaramillo sees the future of renewable energy in thousands of rusting iron pellets in a laboratory in Somerville, Massachusetts.

Jaramillo is managing director of Form Energy, a company that recently announced what it says is a breakthrough in a global race: how to store renewable energy for long periods of time.

The traces of rust on iron have been a sign of decay for thousands of years. But now that chemical process – the oxidation of iron to iron oxide – forms the basis of a battery that Jaramillo said could offer a way to store energy on power grids for more than 100 hours, but at about a tenth the cost of an equivalent installation powered by lithium-ion batteries, the advanced battery technology.

“Today, lithium-ion is very cost effective to provide energy storage for a few hours,” said Jaramillo, who previously worked on stationary energy storage for electric car maker Tesla. “But looking ahead and looking at how the network works, we need to be able to bridge hundreds of hours. “

Batteries discharge energy from iron pellets when they “rust” or oxidize in oxygen in the air; the reverse chemical process – effectively “rusting” – then uses electric current to convert the rust back to pure iron. Each iron-air battery is roughly the size of a dishwasher, and thousands of these batteries could be placed together in a very large building to store megawatts of renewable electricity on the grid until we need it.

Form Energy is far from the only company trying to solve this problem. Renewable wind and solar power now accounts for about 10 percent of the electricity used in the United States. But sometimes the sun isn’t shining and the wind isn’t blowing, and today’s power grid doesn’t have a lot of storage. Fossil fuels like gas and coal, which environmentalists hope to eliminate as energy sources, can power the grid in seconds and have no such shortcomings; it is hoped that grid-wide storage can replace at least part of this “on-demand” electricity requirement.

“Cost-effective, sustainable and reliable energy storage opens up new areas of possibility for grid decarbonization,” said Costa Samaras, associate professor of environmental engineering at Carnegie Mellon University in Pittsburgh, who studies efforts to create a carbon-free electricity grid. emissions. “It reduces stress on the grid during peak hours, and it stores renewable energy when you have a lot of it and when you don’t. “

This can be from minute to minute – when a cloud passes in front of the sun, for example – or at different times of the day, for example when there is no wind during peak periods of demand for electricity in the afternoon and evening. Short-term demands can now be met relatively inexpensively with grid-scale lithium-ion battery installations such as the 250-megawatt Gateway energy storage facility in California.

Although the costs of large “Li-ion” installations have fallen dramatically in recent years, they become expensive when designed to last more than about 10 hours. Renewable energy advocates have pushed to invest in new technologies to enable renewable energy to meet the demands of a modern electricity grid.

While the chemistry behind iron-air batteries isn’t new, they’ve been overlooked because they’re too heavy to be portable. Form Energy said its proprietary technology to extract oxygen from the air through a membrane makes the chemistry feasible for stationary storage, and at a much lower cost than equivalent lithium-ion facilities. They are also safe and made from abundant ingredients, unlike lithium-ion batteries which require an abundant amount of lithium that is difficult to obtain.

Form Energy said its iron-to-air battery installations would cost around $ 20 per kilowatt hour, falling to around $ 10 per kilowatt hour by the end of the decade. For comparison, grid-wide lithium-ion installations cost between $ 250 and $ 300 per kilowatt hour, Jaramillo said. The company is now working with a Minnesota utility on a 1-megawatt storage facility that will be completed in about two years, but after 2025, “we’ll go pretty quickly to tens and then hundreds of megawatts, that is. that’s the kind of scale you have to be to really make a difference on the grid, ”he said.

Iron-to-air batteries are just one of many grid-scale storage ideas, according to Chris Knittel, a professor of applied economics who heads the Center for Energy and Environmental Policy Research at the Massachusetts Institute of Technology.

Others include using standby electricity to pump compressed air into underground salt caverns and then to power turbines when electricity is needed, or using electricity to make electricity. ammonia, which can be stored and then used in fuel cells to extract energy.

“There are even ideas of using electricity when it is cheap to drive a train up a hill, park it and then use it to generate electricity as it goes down”, did he declare.

Some areas have hydropower systems that can store electricity in the form of “pumped hydropower” by pumping water upstream to a reservoir, for example, and using it later to drive turbines, but many regions will need large-scale battery storage to support renewable sources of electricity. like solar and wind, he says.

Existing methods of short-term electricity generation, primarily by burning fossil fuels like natural gas, have so far succeeded in smoothing out intermittent supplies from renewables, but not for long.

“We’re all trying to think of a system where there’s no natural gas,” Knittel said. “In this world, batteries are going to become important, even necessary. “