Redflow of Australia makes ‘the world’s smallest’ zinc bromine flow batteries at 10kWh each for residential applications. The group recently installed their largest residential system – a 60kWh off grid battery system to combine with 18.7kW of solar power.

The installation cost a similar amount as connecting the home to the power grid 2.7km away.

The newest version of the hardware, seen in the featured image above, is part of a broader solar+storage installation that includes:

Six Redflow ZCell zinc-bromine flow batteries, two Victron Quattro 48/10000 inverter/chargers and 72 260-watt Tindo solar panels, with an 18.72 kilowatt peak (kWp) capacity.

The Redflow batteries come with a ten-year warranty that allows you to discharge your battery system every single day to 100%. Flow battery manufacturers often suggest that their hardware will run for greater than 20 years without any energy storage degradation.

A separate system on the company’s website, built out of two of the 10kWh units plus 5.2kW of solar, costs approximately AU$56,000 installed.

The below unit is the flow battery without the good-looking external case. The larger batteries – shipping container size – contain up to 60 individual units like this stacked inside.

In April of this year, Redflow halted shipments of their hardware after ‘laboratory testing of electrolyte samples of 10 batteries found a “potential failure risk” due to “impurities” in the fluid.’ Redflow has, obviously, restarted shipments since that time.

Redflow made a recent announcement that they had signed a contract with a manufacturer in Thailand to build 250 10kWh units per month, for a total capacity of 30MWh/year. The manufacturer already builds several components for Redflow, and the two expect to drop an additional 10% off the cost of the hardware with this scaling. In July, Redflow announced $14.5m of funding had been raised for this expansion.

A 2015 Phase 1 test by the US Department of Energy confirmed that the hardware runs at the levels specified by the manufacturer. Longevity testing occurs in Phase 2. A longer technical description of how a flow battery works can be found on

Other types of flow batteries exist as well. A vanadium ion model is currently being built-in China that is the world’s largest battery based energy storage system. This 200MW/800MWh system will be half competed by the end of 2017, and is expected to come online in 2018.

This summer, ViZn Energy put out a press release that they could offer solar power 24/7 via its zinc iron flow battery solution at 4¢/kWh. This very low price – lowest I’ve personally seen – of 4¢/kWh for electricity from a battery system was made possible by strategically sizing their 30MW/120MWh battery with a 100MW solar power system in Arizona.

Recently, a water treatment plant in Queensland, AU installed a 95kWh Tesla Powerpack plus about 90kW of solar power for $1.5m. This system also was priced similarly to the cost it would have been to connect to the local power grid.

Fully Charged did video outtake on the Redflow hardware a few months back:

Electrek’s Take

The two most common arguments against flow batteries are that their energy density isn’t great enough and that their upfront costs were significantly greater than lithium-ion. As a result, the conventional knowledge has been that flow batteries would only compete with Lithium Ion in large power grid deployments where scale could save money, and longevity was worth more. Redflow has shown that the size argument is no longer viable.

Update: The manufacturer pointed out, as added in the story above, that a 20kWh storage + 5.2kW solar costs AU$56,000. The solar system will cost roughly AU$2.20/W – $11,400 (this is higher than an average install because off grid solar costs a bit more due to extra hardware). Meaning the 20kWh of energy storage costs about $44,600 – $2,230/kWh (which is actually about USD$1730). That’s a healthy $/W installed for energy storage – however – the manufacturer makes a fine point in the above video – if you consider the levelized cost of energy over the lifetime of the hardware, you’ll find the cost per kWh of electricity provided is actually lower than a lithium ion battery pack if you account for degradation over the long term. I’d have to see further math to give an educated opinion.

The main benefit that flow batteries bring to the table is their longevity. Other than hardware pieces breaking – there is no natural degradation process. These units can run at 100%, every day, for as long as you’ll be alive. In fact, per some technical reading, its actually required for best performance that the units run to 0% every few days to help manage the units over the long term. 100% after 20 years is impressive…however…if the lithium ion in Tesla’s units can get cars batteries to run for 500,000 miles, maybe the distance ahead in the longevity race is lesser than suspected.

That the world’s largest under construction battery is a flow battery says that lithium ion has some competition. Good for us buyers of technology.

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