Redflow's home batteries to start shipping in June

South Australian energy storage outfit Redflow has started taking pre-orders for its home battery, dubbed the ZCell, but please don't pitch it against the Tesla PowerWall.

The comparison is probably inevitable, but Redflow chairman and Tesla 'leccy car owner Simon Hackett told The Register the company is not after the entry-level home solar user.

Its 10kWh offering isn't going to compete with the PowerWall on installed price, Hackett said, but on per-kWh cost.

The ZCell's most important differentiator is that unlike either lead acid or lithium batteries, it's designed for 100 per cent discharge, rather than (for example) the 50 per cent discharge limit of lead acids.

“The PowerWall is about 6.4 kWh hours installed for around AU$10,000 in Australia,” Hackett told us. “We believe we're about the same in terms of dollars per installed kWh.

“If you don't need 10 kWh, you'll want to go and buy the pretty one,” he continued.

“This isn't a entry-level device.”

From a market point of view, Hackett's comfortable with the idea that Tesla will shift more volume in the short term: “I think in the next five years, the use-cases for bigger batteries will multiply.”

The rise of electric cars alone should give that a boost: Hackett's own experience is that his regular consumption from his Tesla Model S is about 10 kWh.

Hackett might refer to the PowerWall as the “pretty” battery, but Redflow has put effort into making the ZCell enclosure less confronting than lead acid batteries.

And smaller, at 1,000 mm long, 1,150 mm high and 500 mm wide.

Inverter certification

One of the things Redflow is working on ahead of shipping is to get inverters certified to work with the ZCell.

The Register asked why this would be necessary: doesn't the inverter just need to provide the red and black cables to charge and discharge the battery?

“The big fat connections are the usual 48 volt cables. You present the battery with more than 48 volts to charge it, or you suck power out.”

However, because (like the PowerWall) the ZCell has an onboard battery management system (BMS), there are good reasons to get the interfaces right – for example, to give the inverter detailed battery status that can be reported back to the user (or all the way up to cloud-based control systems).

That's where the certification matters, even if it's just hooking into simple relays that tell the inverter whether the battery is charging or discharging.

More sophisticated inverters use CAN (controller area network) BUS interfaces to get a second-by-second state-of-charge update.

“We're completing our side of the CAN BUS interface now. That's the preference, so that your inverter has a very high fidelity idea of what the battery is doing,” Hackett said.

That's not a requirement for operation, however: “You can run ZCell without knowing that, just run it with your eyes shut, and ask the battery management system.”

Margin for the channel

Redflow says the batteries will ship at between $17,500 and $19,000 installed, and Hackett said the wide error bar is to make sure installers have a margin that lets them make a living.

“We don't want to garotte the installers,” he said, adding that with “strong interest” there'll be no shortage of resellers, which should also help keep the price towards the lower end of the estimate.

Hackett said the batteries are being manufactured now, at Flextronics in America, the enclosures are pretty much ready, and the battery management system is getting its final polish.

The first run should be ready to ship by June, and the company is currently working on its international launch plans. Pre-orders and FAQs are here.

The Register has an explanation of Redflow's flow battery technology here. ®