Wednesday 5th December 2018

Wind Watch

Is zinc the missing link for energy storage?
By Richard Heap

This is an analysis piece written by our Editor-in-Chief Richard Heap for Energy Storage Report and published on 28th November.

When I started writing for ESR in September, I didn’t realise how vital the periodic table would be in my life. But I’ve done lithium, I’ve done vanadium, and now it’s the turn of zinc. Is this the real future of energy storage?

Potentially. I expect you’ve heard about zinc-air batteries that have been developed by firms such as Nant Energy. In September, Nant announced that it had built the first scalable, rechargeable and commercially-available zinc-air battery storage system. You can read more about this in this article in the New York Times.

But batteries aren’t the only possible solution. We spoke to James Larsen, chief executive of Toronto firm e-Zn, about its system, which can use a dual power cell to create, store and discharge electrical energy from zinc.

He says this system would help to provide long-duration energy storage that supports renewable energy projects, including wind farms and solar arrays. This is a different approach from companies developing zinc-air batteries.

How does it work?

e-Zn was founded by founder and executive chairman Gregory Zhang, who spent the 20 years before e-Zn at Teck Resources as scientist and R&D manager. He also wrote a 1996 book on zinc’s electrochemical properties.

Larsen says a big difference between zinc-air batteries and its power-cell-based system is that the former are device-based systems and the latter is materials-based.

By that, he means device-based systems, like batteries, are where energy is stored in the same place as the energy conversion technology. This means that the amount of energy stored and the amount of power that can be produced are intrinsically linked, with the result that the only way to scale up storage capacity is by adding more batteries.

By contrast, e-Zn’s system is materials-based, which means that the electrical energy is stored in a material that can be held separately from the power-generation tech. Its Zn Reactor is made up of a charging section, a storage section containing potassium hydroxide with dissolved zinc in it, and a discharging system.

He explains: “We use electrochemistry to generate zinc and store energy in the metal. We just produce produce produce zinc. Then whenever we need the energy, we just dissolve the zinc using our air cathode and that produces the energy.”

Larsen says one benefit of this system is that it can keep producing zinc indefinitely, and this zinc can be stored without any loss in its electrical capacity. This means its systems should be appropriate for long-duration storage.

It also means e-Zn could increase either the system’s energy storage capacity (by using a bigger storage section) or power output (by using a more powerful air cathode) independently of each other. This means the system is more cost-effective and flexible than rivals.

The best comparison is with pumped hydro, which is where excess power generated by, say, a wind farm is used to pump water from a low level to a high level and stored in a large reservoir. The water is then released to flow downhill and turn a turbine when power is needed.

He says: “Those are independently scalable. You could have a 1MW turbine and a reservoir of water for ten hours. That would be a 10MWh system. But if you made the reservoir a bit bigger – 15-20 hours – then all of a sudden you have a 15MWh-20MWh system.

“The power of e-Zn’s system is determined by the surface area of the electrodes and the energy is determined by the size of the cell. Our ability to scale energy without scaling the power is what enables economic long-duration storage.”

Reaching commercial maturity

The business was founded in 2012 and currently has a demonstration project where it has paired its system with a solar array. The company is working with partners including Canadian Solar, and the scheme has been funded with C$700,000 ($530,000) from the Canadian government. This has enabled e-Zn to verify and demonstrate its performance characteristics at scale.

The firm is now raising Series A financing to support its growth through to 2020 and the commercialisation of its system. Larsen wasn’t prepared to discuss details of the fundraising as he said it is at a sensitive stage.

However, he identifies that the biggest potential now for the technology was as a renewable alternative to diesel generators, including in remote locations.

“There was an announcement recently about this military base going ‘renewable’ and, if you read the details of their renewable system, it was a 10MW solar array, 5MW battery and 5MW diesel generator, because they can’t make the economics work if it’s just renewables and batteries. With our technology, we actually can.”

There is still a way to go for the technology to reach commercial maturity, but we’re always happy to hear about systems with the potential to shake up incumbent fossil fuel systems. And we’d love it if a zinc-based technology could help consign projects that pair clean energy with diesel back-up generators to the past.