Slip-streaming Tesla, Oz battery-maker plots home-biz launch

Redflow tweaks telco electron-buckets to take on Tesla

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Australian battery researcher and manufacturer Redflow is hoping to get a jump on Tesla, prepping its own entry into the residential battery market.

The news puts yet another player into what used to be regarded as a tight niche. Home storage was strictly a matter for the off-grid user, and it wasn't until recently that the Brisbane company decided it was worth a shot.

Before that, as recently-appointed chairman Simon Hackett explained to Vulture South, the company had its eyes firmly on a business market – specifically telcos wanting to power remote cell towers.

Hackett is perfectly happy to acknowledge Elon Musk's contribution to the market: “Tesla set the concept of energy storage alight” he said, at a time where Redflow was at “that interesting nexus between making a pretty cool battery and convincing the world to buy lots of them”.

And while there's no Redflow “Gigafactory” under construction anywhere, the company had already nominated America's Flextronics as its manufacturer, so it can scale-up as global demand rises.

Redflow's batteries were designed to sit at the bottom of telecommunications towers, he explained, and only lacked the right interfaces to plug into the home market.

The batteries have to be integrated into existing power systems, but that isn't so difficult: “The missing link is a controller unit that we're going to produce here in Adelaide.”

Once the controllers are configured to the charge controllers in existing solar inverters, Hackett said, the Redflow battery is a drop-in replacement for lead acids – “just plug it into the red and the black cables”.

Why not plug and play?

Vulture South asked why a controller interface is necessary, and Hackett said simply “there are two sorts of batteries in the world: lead acid, and everything else”.

Lead acid batteries are sensitive to how they're charged, making the charge controller an important piece of the solar power electronics. Those charge controllers infer the state of charge from the voltage of the battery bank, and that's where lead acid is different from “everything else”.

The lithium batteries that Tesla is using, and the zinc-bromine flow batteries Redflow is producing, use technology-specific battery management systems.

It's the battery management system that needs the interface, to tell the charge controller when to stop. Instead of a granular response to (in the example of a nominal 48V battery bank) voltages between around 45V (stop drawing battery power) and 56V (stop charging), the battery management system just needs to signal full-or-empty to the charge controller.

“In telco applications you're feeding rectifiers – it's dc all the time, and that makes it easier. To run an AC inverter, you have to place that little bit of interface to make it work. It's a shim that turns it from a telco device to an everywhere device.”

Accidental consumer appeal

The other piece of good fortune, Hackett said, is that the company's designers had been concentrating on features that happen to play well in the home market: a ten-year battery life to satisfy telcos' demands for remote sites; zero-maintenance, also for the remote site market; and the ability to be discharged from 100 per cent to empty on a daily basis.

Does that sound over-engineered for the home market? It's not. The long life, he said, makes the economics stack up (prices haven't been finalised for the home battery, but by way of example he suggested $15,000 over ten years is easily recoverable in grid savings).

The deep discharge capability means consumers either in off-grid or where the grid is unreliable don't need to learn how to “read the meter” to make sure they're not risking the battery life, and zero-maintenance also plays to the suburban user.

Grid-connect applications get another benefit from the very deep discharge: “you size the battery to match the grid loads, because you get the best return by using 100 per cent of the battery.

“If the battery is too big, you lose out,” he explained.

Lead acids, on the other hand, demand a considerable derating to avoid excessive discharge; lithium is better on this score, but still can't suffer repeated excessive discharge.

Know your limits

There are trade-offs, and before the commercial launch into the home market, the company will be working to understand those.

One thing that lead-acid batteries handle very well is spike loads, such as are drawn by electric motors at start (switching on the air-conditioner, for example).

Neither lithium batteries and Redflow's zinc-bromines can match the instantaneous capacity of a lead-acid.

“If you have a power application where you have spiky power demands, the answer is either change the power demand, or in some cases, it might be a hybrid.

“You could use a few lead acids for spike handling, and our batteries for the underlying demand.”

However, he said, it would be unusual for a home to have spikes so large that the ZBM's 120A-plus maximum capacity wouldn't cope.

A long-time solar user both for his home and charging his Tesla, Hackett will be a field trial for the battery: two ZBMs of 10 kWh each which will be about half the weight of his existing 24 x 2V lead-acid banks.

Skills in short supply

There's another gap in the market, but it's not specific to Redflow: people, in particular, those with the skills to scale a battery set correctly for a given customer.

Every battery has an efficiency sweet-spot, and in the case of the ZBM, that's at about 60-70 A output. At higher current, the batteries operate less efficiently and discharge faster.

“We have to choose decently smart people,” Hackett said. “We very much want the expertise – we're not set up to do end user support.”

To make it easier for the channel he hopes will emerge, Hackett says Redflow is getting the batteries a pass-mark from the major inverter vendors.

He's also keen on how the computers behind control systems can help make the battery life easy for users.

“The computer system can see the future, unlike power systems of old. That matters: the strategy you'll apply tomorrow is something you need to react to now.

“If the weather forecast says there's rain tomorrow, tonight you want to fill the battery with grid power at off-peak rates.”

The aim is to be more dynamic: “Learn about the observed usage habits, and starts adapting how [the software] manages the energy systems.” ®

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