The UK looks set for the arrival of energy storage in a big way this year. Excitement is understandably mounting over Tesla’s entry into the UK, with the first Powerwall installed in Wales at the beginning of this month while other rival lithium ion – and some lead acid – battery storage system makers are also targeting the residential market.

However, while these companies and their battery chemistries are fighting it out for both market share and brand awareness, several energy storage systems have been deployed already on a commercial basis using a more novel storage technology – the saltwater battery.

Developed and manufactured by Aquion, the aqueous hybrid ion (AHI) battery, to give it its proper name, was created by the company’s CTO and founder, Professor Jay Whitacre. Whitacre’s work on the battery won it the US$500,000 Lemelson-MIT Prize, which honours technological innovations that can “improve the world” from mid-career inventors.

“We started evaluating Aquion at the time they started manufacturing in June 2014,” says Dennis Garrison of Solar PV Partners, which is a dealer for the AHI in the UK.

“We did a full review of everything that was out in the marketplace of about 14 major companies and decided we wanted to go with a sustainable, clean, non-hazardous product. One that was cost-effective by comparison to the others and one that is scalable too”.

Solar PV Partners starting selling Aquion in April 2015, as Elon Musk prepared Powerwall for its big unveiling and not long before the UK government’s seeming antipathy to renewables caused it to bring down the axe with 65% feed-in tariff cuts for solar.

Garrison and his colleagues Mark Hartung and Richard Ritchie said that they were developing commercial solar projects around three and a half years ago before deciding to move out of that aggressively competitive space while remaining in a related area. After weighing up their options, which included BIPV and storage, they chose storage as a focus and Aquion’s AHI as a vehicle for that.

“Unlike any other form of battery today it’s as benign as possible to the environment from its creation, inception, through its use and more importantly through its recycling process. If you look at the recycling processes for lead acid, they’re rather expensive,” Hartung says.

“When it comes to any form of lithium the recycling processes are cost prohibitive and environmentally suspect, not to mention energy intensive.”

Ritchie explains the 'benign' properties of the inside of the battery.

“It's an amazing product. The anode and cathode are powders, when they’re put together, and once they’ve been put in and been infused and the battery’s used, they go back to being a powder and the charge and discharge, the ionic fluids are diffusing right down into this, so it’s at depth the storage takes place. It’s one of the reasons why it’s such a robust chemistry and why it’s so insensitive to what other cells would treat as abuse. You can 100% discharge it, you can cycle it at partial states of charge.”

When dismantled, the powder inside the batteries is clean enough that inventor Jay Whitacre has joked that he could safely eat it.

Aquion's UK evangelists

Energy Storage News has covered several Aquion installations globally since 2014. The first in the UK was a 25kWh commercial, on-grid system on farmland in Northern Ireland, with Solar PV Partners the supplier of the battery and Wattstor as installer. Installed in just a day and a half, at the time Wattstor director Michael Danes also hailed the sustainability of the battery technology including its potential 15 to 20 year lifespan.

According to Solar PV Partners, even for them, the capabilities of the battery shown by the second UK installation shortly afterwards were a pleasant surprise. The company deployed an AHI system to the Eurotunnel entrance, where it is being used to power the tunnel sign. The off-grid system has a 9.2kW solar array to power the sign during the day and Aquion batteries to power the sign at night.

“In January to our surprise, because it was so dark and it rained every day, they didn’t turn on the solar, they just ran the Aquion for the first seven days, 24/7 in fact, without discharging even 50% of the batteries,” Hartung says.

Another company working with Aquion batteries in the UK, Circuitree, launched its AHI-based systems with integral energy management at last year’s Solar Energy UK show. Company director James Dean recently fitted out a bus which will be used to educate refugees and other displaced peoples living in temporary camps in Calais. It will use 2kW of PV on the bus’ roof, 10kWh of storage from the saltwater batteries.

Dean even came up with a novel crowd-funder idea which he says he came up with for fun over last Christmas. He wanted to raise £12,000 to build Glacius White, an “everlasting snowman” which would be an entertaining and educational way to spread the message about PV, batteries and sustainability.

While Glacius White was a light-hearted way to raise awareness of the technology and environmental issues alike, Dean says he has put the idea on hold for the time being to concentrate on other, more serious projects.

Through affiliated distribution company CPH Solar, of which Dean is also a director, he is now also selling Aquion batteries paired with inverters from German maker KACO. Dean’s co-director at CPH Solar, Carsten Pump, wrote recently that the systems “cost the same as lithium ion” but can be cycled twice as many times in their respective lifetimes.

Commercial scale calling

Going forward, Solar PV Partners claim they have attracted serious interest from the commercial sector and while unable to give further details for confidentiality reasons, says that one of Britain’s major food retailers is among those considering using the batteries to store and shift power to mitigate its cost of energy through TRIAD and other peak or time-of-use pricing-based mechanisms.

While it can be scaled up from a 1.5kWh residential block to multiple megawatts, the battery’s long duration-suited storage, however, is not as good at high power applications such as frequency response.

“AHI is good for the longer duration daily cycles of power,” Richard Ritchie says.

“It’s not so good for a quick burst where you want to get all the power out, like fast-frequency response where you want a vast amount of power in a very short time and want to drain the battery. Peak mitigation and load shifting is where it really performs well.”

Energy Storage News' publisher, Solar Media, will be hosting the Energy Storage Summit at Twickenham Rugby Stadium, London on 28 April.

James Dean of Circuitree on the Aquion battery: