ZCell Battery Review: Better Than Lithium-ion?

redflow zcell vs powerwall etc

How does the Aussie Redflow ZCell compare to lithium ion batteries?

Note: the Cell battery has been superseded as Redflow continuously improves its product. The latest version of Redflow’s battery is called the ZBM3.

The Australian company Redflow is accepting pre-orders for its new home energy storage system, the ZCell battery.  It has a 10 kilowatt-hour usable storage capacity, can provide 3 kilowatts of continuous power, and is suitable for on-grid and off-grid use.  Deliveries will begin in August 2016.

In this Z-Cell battery review I go deep into the zinc bromide technology’s pros and cons compared to its main challenger: lithium ion batteries.

While there are many lithium-ion storage systems on the market, the Redflow ZCell stands out as the only zinc bromide flow battery.  Its unique chemistry gives it several advantages over lithium-ion systems.  One is it can lie dormant for long periods at any level of charge without suffering from deterioration.  And another is its storage capacity will never decline over its over its entire lifespan. 

Multiple ZCell batteries can be installed to provide additional power and storage capacity. It is designed for outdoor installation and weighs 240 kilograms. It will come with a comprehensive product warranty of 10 years or 30,000 kilowatt-hours, whichever comes first.  If fully cycled once each day it will take 8.2 years to reach the end of its warranty.  As most households are unlikely to use it at full capacity, many people could buy a ZCell and be confident they won’t be out of pocket if a fault develops for 10 years.

Is A Zinc Bromide Battery As Good As You Zinc, Bro?

The chemistry of the ZCell battery is very interesting.  It is, at its heart, a reversible electroplating machine. When the ZCell is charged, electrical current is sent through the battery which causes zinc to be removed from zinc bromide and electroplated onto plastic electrodes. When the battery is discharged, the opposite happens and zinc is removed from the electrodes and attached to bromine to make zinc bromide and an electrical current is produced.

So, yes, I’ve pretty much said you can run a battery off cheap jewellery and galvanized iron.

The chemical process is completely reversible, which means the ZCell battery’s energy storage capacity never declines. Unfortunately, it will stop working at some point, but, fingers crossed, not for a long time.

Are Zinc Bromide Batteries Safe?

toxic sign

Zinc Bromide is Toxic

Is zinc bromide safe to handle? Hell no! It’s toxic. If you drink that stuff, you’ll die. However, you will be safe if you remember to follow this one simple safety procedure: Don’t drink zinc bromide. If you can manage to do that, you should be fine.

There are about 125 liters of reddish hued zinc bromide solution, at 20% concentration, that weighs around 150 kilograms in the ZCell battery. And if I remember my high school chemistry correctly, and yes, I am so lazy I would rather try to remember something I learned a zillion years ago than actually bother to type something into Google, the more dilute it is, the less dangerous it is.  And so the fact that it is mostly water is great news if you decide to splash it on like some sort of toxic aftershave. It should really reduce the irritation.

But unless your hobby is shooting rifles at random objects in your backyard, you should never come into contact with the zinc bromide solution.  The bromine that is formed when the battery is charged is stored as an oil inside a thick polyethylene tank inside another thick polyethylene tank.  The zinc bromide is kept in the outer tank.  And the entire battery sits in a metal enclosure which has another tank designed to catch any fluid in the unlikely event that leakage does occur.

Zinc bromide solution doesn’t evaporate easily, so if it is spilled it will just tend to sit there.  But it is likely to give off a small amount of bromine gas and this gas could also be potentially released directly from the battery.  However, this gas comes with its own built in safety system. Bromine comes from the Greek word brómos, which means stench. So if there is leaking bromine gas you will know about it and you won’t want to hang around.

Zinc bromide is not a teratogen. This means two things. Firstly, it is not a monster from Doctor Who. And secondly, it does not cause birth defects. In other cheerful news, it does not cause cancer. Or at least it doesn’t cause more cancer than stuff we normally don’t consider to cause cancer such as vegemite or wood.

I could go on about its health effects and exactly how much zinc bromide solution you can drink before you need to call an undertaker, but I don’t think that would really be fair on the flow battery. After all, I don’t tell people not to break open their lithium-ion batteries and eat the insides. And I also don’t warn people not to drink petrol or shower in it. So basically, what you need to know is, the ZCell battery is not bloody likely to emit bromine gas. If it does emit bromine gas you’ll bloody well know about from the stench. If it somehow leaks zinc bromide out of both the battery and its enclosure, you’ll know about it from the literally bloody colour. And I’ll assume you’re not bloody stupid enough to try to lick it up.

Every time something new comes out people have a bad habit of focusing on any potential negatives, while ignoring the fact that everyday activities such as driving a car are far more dangerous than installing a zinc bromide or lithium-ion battery.

We shouldn’t fear the new. Except for babies. Those things are terrifying.

The ZCell Never Declines In Storage Capacity

The ZCell battery can be discharged 100% every single day without suffering any harm at all, which is very different from other battery chemistries on the market.  In addition it does not decline in storage capacity over time.  It starts off with 10 kilowatt-hours on the day its first turned on, and it will have 10 kilowatt-hours on the day it dies.  And according to Redflow, for a family that uses it at 80% capacity, that’s likely to be around 14 years later.

In comparison, the Tesla Powerwall is a 6.4 kilowatt-hour battery and only 5.44 kilowatt-hours of that is actually warranted to be usable.  But after the first 2 years that drops to 4.6 kilowatt-hours.  And 3 years later it drops down to only 3.8 kilowatt-hours of warranted storage. So after 5 years it would take 3 Tesla Powerwalls to have the same warranted energy capacity as the ZCell.

While the Tesla Powerwall is the poster child of not being able to keep its kilowatt-hours up, every battery that isn’t a flow battery like the Redflow ZCell will decrease in capacity over time.

The ZCell Can Rise From The Dead


The ZCell can rise from the dead

At any point when it is charging or discharging the ZCell battery can be put into hibernation mode and be left as it is for as long as you like without suffering any harm.  And it will maintain whatever charge it had at that point for potentially decades.  This is very different from other battery chemistries which will gradually lose charge if alone and deteriorate once they’re completely drained.

However, the Redflow ZCell can raise from the dead 3 days, 3 months, or 3 years or more later and continue operating as if nothing had happened.  Some external power will need to be supplied to get them going, but not much.  For an off-grid system a hand crank should be sufficient.

This ability to completely shut down at any time without harm and without losing stored energy makes them ideal for applications where they might only be used occasionally, such as holiday homes or seasonal businesses.

The ZCell Is Very Unlikely To Start A Fire

The good news is bromides are a flame retardant, so unlike lithium-ion batteries, the electrolyte is not flammable. The bad news is if there is a serious fault it is still potentially possible for the battery to give off hydrogen, which is explosive and doesn’t give a damn about flame retardants.   However, the chances of the ZCell giving off a dangerous amount of hydrogen when installed in an outside location appears extremely small to me.

If you are wondering where hydrogen can come from in a zinc bromide battery, the electrolyte solution is mostly water which will produce hydrogen when current is passed through it.

Operating Temperature

The ZCell battery operates with an electrolyte temperature from 15 to 50 degrees Celsius, which is not the same as ambient air temperature.  If the temperature of the electrolyte falls out of this range the battery will shut down, but won’t be harmed.

Because the ZCell has a lot of thermal mass, generates heat when charging and discharging, and has a fan to blow off excess heat, I wasn’t sure just what this meant for its operation in different Australian climates, so I called Andrew Kempster, the Sales Director of Redflow, and he assured me that provided the installation was appropriate for the location, that is, not exposed to direct sunlight in the middle of Cunnamulla, then the ZCell was expected to function without problem in places that are hot in summer, such as central Australia, and cold in winter, such as Canberra.

Of course, if the ZCell ever does shut down because of low temperatures, just because I said bromides are a flame retardant does not mean it is okay to set it on fire to get it started again.

The Redflow ZCell Is 100% Recyclable

All components of the ZCell are completely recyclable.  One could be pulled apart right now and all the plastic and metal could be fully recycled using currently existing methods.  The zinc bromide solution can be cleaned and reused in another ZCell.

Where Is The ZCell Manufactured?

Redflow is an Australian company and they designed, prototyped, and tested their zinc bromide battery technology here. However, because Australia’s mining and agricultural industries export so much, it does make it difficult to manufacture things here.  As a result, the ZCell is made overseas, under license, by a Singapore based company called Flex, which carries out production in Mexico.

Flex, or Flextronics, as it is also known, made my original xbox and it still works, so that’s a good sign. But oddly enough, the Redflow website doesn’t say the ZCell battery is made in Mexico. They just say they are made in North America.

For the benefit of those who don’t speak marketing, I will explain that when companies talk about manufacturing locations, Canada means Canada, the United States means the United States, and North America means Mexico. Why they don’t just say Mexico, I don’t know. After all, I think we as a country have moved past the horrors of the Great Cane Toad/Mexican War of ’87.  And we’re probably not dumb enough to assume the ZCell is full of tequila just because it comes from Mexico.

The ZCell’s Warranty Is Excellent

The ZCell will come with a comprehensive 30,000 kilowatt-hour or 10 year warranty which will cover any faults it may develop in that time.  And the warranty covers 100% of the battery’s capacity for that period, unlike lithium-ion batteries which typically only cover 80% of their original capacity, or 56% in the case of the Tesla Powerwall.

This is extremely impressive.  While the ZCell battery only has three moving parts, which are two pumps and a fan, pumps do have a bad reputation for breaking down.  However, with proper engineering they can last a long time.  My parent’s pool pump has lasted for 15 years. I know this because they keep bringing it up.  “What’s that, Ronald? You’re out of work again? You know our pool pump has worked reliably for 15 years and we didn’t even pay to put it through university.”  Personally, I’ve never had a pump last that long.  All my ex-wives used to complain to me about a lack of reliable pumping.

Expected Operational Life

Redflow expects the typical ZCell to exceed its warranty by one third and provide 40,000 kilowatt-hours of stored electricity in its lifetime.  If used at full capacity it would take 11 years to reach that point, and if used at 80% of capacity it would last for reasonably close to 14 years.

Disadvantages Of The ZCell Battery

There are a few disadvantages to the ZCell and zinc bromide batteries in general:

  • Their efficiency is lower than lithium-ion batteries.
  • Their power output is lower per kilowatt-hour of storage than most but not all lithium-ion batteries.
  • A single ZCell is large and heavy.
  • They are not well suited for indoor installation.
  • They need to fully discharge and shut down for around two hours to purge their electrodes of zinc every week or so.
  • Just like lithium-ion battery systems, they are very unlikely to save you money at current prices.

The ZCell’s Efficiency Is Low

The DC to DC roundtrip efficiency of the ZCell battery is around 80%. This means for every kilowatt-hour of electrical energy put into the battery, only 0.8 kilowatt-hours can be taken out. For a zinc bromine battery this is amazingly high. The Redflow company has clearly done a fantastic job of maximizing the efficiency of their ZCell battery.  Unfortunately, it is still worse than the efficiency of lithium-ion battery systems. For example, the Tesla Powerwall claims to have an efficiency of 92.5% and the LG Chem RESU 95%.

The 80% figure applies if the ZCell is charged with DC from solar panels. This is called DC coupling and is the most efficient method. However, if it is charged with AC, a situation called AC coupling, the efficiency of the ZCell, or any other battery system, takes an additional hit and the overall efficiency of the ZCell battery can easily drop to 70% or less.

Low Efficiency Is Not A Major Problem

A low round trip efficiency of 80%, or even 70%, is not as bad as it may seem for the economics of a battery system. This is because the feed-in tariffs for solar electricity exported into the grid are now far lower than the cost of grid electricity.  If a household only receives a 6 cent feed-in tariff, then with 80% efficient energy storage it will effectively cost them 7.5 cents to store one kilowatt-hour. But if this saves them having to pay 30 cents for one kilowatt-hour of grid electricity in the evening, then it is worthwhile – if the cost of storing that kilowatt-hour comes to less than 22.5 cents. The ZCell won’t store a kilowatt-hour of electricity for less than 22.5 cents, but if it did, it would pay for itself despite having low efficiency.

Its Efficiency Is Likely To Decline Over Time

While the capacity of zinc bromide batteries doesn’t decline over time, their efficiency does, as is the case with all batteries.  I don’t know if the decrease in efficiency will be better or worse than a typical lithium-ion battery system, but I have been told that the decline in its efficiency percentage should be a single digit over the course of its lifetime.  So probably less than a 1% decline a year.

The ZCell May Be Worse For The Environment Than The Competition

Under the right circumstances it should be possible for home energy storage to reduce greenhouse gas emissions. However, at the moment, when used on grid it is likely to increase greenhouse gas emissions.  This is because one kilowatt-hour of solar electricity exported to the grid will reduce fossil fuel generation by around one kilowatt-hour, but storing one kilowatt-hour of solar electricity at 80% efficiency for later use will only reduce fossil fuel generation by around 0.8 kilowatt-hours.  And since the efficiency of the ZCell battery is lower than that of lithium-ion systems, it may be worse for global warming.

In the future when our renewable generating capacity has expanded, energy storage will allow us to kick fossil fuels off the grid.  But if you are thinking of installing battery storage on-grid, be aware that at this point in time it does not help the environment. As far as keeping the icecaps intact is concerned, you are far better off spending your money on buying your sister a rooftop solar system. Or if you don’t have a sister, buying my sister a rooftop solar system.  Alternatively, you could expand your own rooftop solar or invest in energy efficiency measures such as insulation, heat pumps, or a bicycle.

The ZCell’s Power Output Is Low

The ZCell can store 10 kilowatt-hours of electrical energy, but can only release it gradually, so its power is lower than that of most, but not all, lithium-ion battery systems. It can supply power at a continuous rate of 3.0 kilowatts which is less per kilowatt-hour of storage than all lithium-ion systems I am aware of, except for the Enphase AC Battery.

However, it can supply up to 5 kilowatts for a limited period of time. When fully charged and at an optimal temperature, it is capable of providing that much power for over 30 minutes.

If you have two ZCells you’ll have double the available power.  Three will be triple, four quadruple, and I’m sure you can work out the rest on your own.

The moderately low power is not a major problem for on-grid use as extra power is available from the grid when needed.  It can fully discharge in around 3 hours, which means it can be reasonably effective at using most, or potentially all, of its stored electricity during a peak price period for those on time of use tariffs.

People living off-grid with a single ZCell would have to be careful not to draw too much current in the evening.  However there are many people at the moment living off-grid with quite small lead-acid battery systems, so having a single ZCell should be a step up for them.

The ZCell Has Considerable Weight And Size

redflow zcell next to humans

It’s a biggun.

Redflow describes the ZCell battery as being, “theft resistant”. That’s one way of putting a positive spin on the fact their battery system weighs 240 kilograms. That’s heavier than I am. Even if a determined thief did try to steal it, after they collapsed you could just call the police. Or perhaps an ambulance. Unless of course, the thief is my first wife. She could make off with it, no problems.

The ZCell is one meter long, 50cm wide, and 115cm high. It requires a forklift, crane, or lifting device to put in position. Note that Australian work health and safety regulations prohibit the use of a man called Hodor as a lifting device.

While a single ZCell is very heavy, which complicates installation, it doesn’t compare too badly to some lithium-ion storage systems.  After 5 years of use it would take 3 Tesla Powerwalls to provide as much warranted energy storage as the ZCell battery and, since they weigh 100 kilograms each, that comes to considerably more weight than the ZCell.

The Best Location For The ZCell Is Outside

The ZCell is designed to be installed outside, against a wall. It can be installed inside, but when in operation it will make a burbling sound.  It has a fan that will make noise when activated, although not nearly as much as some energy storage systems. It is also possible that it will, on rare occasions, emit a very small, non-dangerous but stinky amount of bromine gas. For this reason it is recommended it be attached to a ventilation duct that leads directly outside and definitely not to your sister’s bedroom.

A Purge Is Necessary To Cleanse The System

In order to continue to function properly, every week or so, the ZCell battery will need to fully discharge and then shut down for 2 hours while it purges its electrodes of all zinc.

For people who are on-grid this is a very minor inconvenience and will pass by unnoticed. For people living off-grid it will be more of a problem, although it can be programmed to occur at the least inconvenient time. For systems using multiple ZCells it is not a real problem, as they will purge themselves at different times.

Purging the electrodes of zinc enables the ZCell battery to continue to operate without a reduction in capacity. It also prevents zinc dendrites from forming. While they sound like another Doctor Who monster, they actually look like tiny feathers and are very pretty, but they have to be purged from the system so they don’t grow large enough to puncture electrodes.

The ZCell’s Cost Means It Won’t Save You Money

Whenever I write about energy storage systems, I always seem to find myself repeating that they won’t save you money. And the ZCell battery is no different.  However, when cycled once per day on solar electricity, as most energy storage is likely to be used in practice, then looking at the cost per warranted kilowatt-hour stored, the  ZCell definitely appears to be a little ahead of the competition.  So while the ZCell won’t save you money, it is likely to get you closer to saving money than other systems.

Redflow estimates the full cost of a ZCell installation will range from $17,500 to $19,500. This includes labour and everything that is required, including a compatible inverter.  And I appreciate Redflow taking everything into account. All too often optimistic estimates of the cost of battery storage rely on the universe spontaneously generating this sort of stuff.

If we assume the total cost of installing one ZCell is $17,500 and it works flawlessly until it has provided the 40,000 kilowatt-hours of storage Redflow expects it to be good for, then $17,500 divided by 40,000 kilowatt-hours comes to 43.75 cents a kilowatt-hour. If it is used at full capacity over 11 years, then including a 5% cost of capital, its total cost will come to 62 cents a kilowatt-hour.

This does not currently pay for itself anywhere on-grid in Australia, and this includes in Canberra and the City of Adelaide which have subsidies for battery storage.  However, while it can’t pay for itself, for many people it is likely to be the modern energy storage system that is closest to being cost effective.

One factor that brings the ZCell closer to paying for itself is days in which it is not used at its full capacity shouldn’t have any effect on its total lifespan, while lithium-ion batteries are always constantly very slowly decaying.  So if a family takes a month long holiday, a lithium-ion battery system would be just a little more dead inside when they get back, while a ZCell will be just the same as it was and can start up again in exactly the same state as when they left.

Who Should Buy The Redflow ZCell?

If you are an early adopter who enjoys having the latest technology, you appreciate an excellent warranty that will give you peace of mind for many years, you aren’t bothered by the fact that home energy storage doesn’t pay for itself yet, and you’d like to support an Australian company and Mexican manufacturing, then the ZCell could definitely be for you.

There are also many people living off-grid who are very interested in the ZCell on account of its excellent warranty, expected reliability, and extremely low maintenance compared to lead-acid batteries.

About Ronald Brakels

Joining SolarQuotes in 2015, Ronald has a knack for reading those tediously long documents put out by solar manufacturers and translating their contents into something consumers might find interesting. Master of heavily researched deep-dive blog posts, his relentless consumer advocacy has ruffled more than a few manufacturer's feathers over the years. Read Ronald's full bio.


  1. this is getting close to the mark. whats the price again ?????

    • Ronald Brakels says

      Redflow says the full installation cost of the ZCell will range from $17,500 to $19,500.

      • Stuart Walsh says

        Hmm, still way too expensive to consider.

        • Malcolm Barko says

          Well I live of both grid connect and stand alone systems and had not had a power bill.Money in front

      • Darren Wilson says

        Hi and thanks again for your interesting writing style. Has the Redflow technology or prices improved since this blog, as I note they have moved manufacturing to Thailand, but their share price has dropped, so wondering if they are still a viable entity top back up any future 10 year warranty claims..

        • Ronald Brakels says

          Well, I hope Redflow will be around long term, but they have certainly suffered some setbacks. If fire safety is a concern — which it should be — it’s definitely a great chemistry to use, but they face very stiff competition from lithium batteries. I suppose it’s possible one bad lithium battery fire could brighten their prospects.

    • This is Kawika with tkoffgridsolar.com,it would seem there are more cost effective and potentially less maintenance batteries readily available on today’s market,most all of the 300 homes I’ve got running off grid here in Hawaii are running sealed agm batteries,with a proper site survey and energy analysis 8-10 yr lifespans easily obtained for a fraction of the cost.

      • Ronald Brakels says

        What kind of depth-of-discharge are the lead-acids running on with that lifespan, Kawika?

      • Stuart J Walsh says

        Can you send me details of what you have there and how many sealed AGM batteries you need to get off the grid please Kawika?

  2. Allan Cuddy says

    How much fully installed for off grid living 24 hours a day 365 days . Panels . Inverter and howmany zcells ?would it take to befully self sufficient.

    • Finn Peacock says


      That totally depends on how much electricity you use and when you use it.

      But even a small, very energy efficient house would be looking at 2 Z-Cells to get through multiple overcast days.

      An average Aussie home would need 3-5 plus a generator for backup.


    • Energy

      A typical Darwin house uses 24kWh per day. If you ran off batteries, you would probably want 3 or more days’ worth of energy storage for clouds etc (these calculations do not consider having a diesel generator).

      3 x 24 = 72kWh = 7.2ZCells.


      This is harder to calculate for someone else without knowing how much power demand that person has. My pool filter pump draws 1.7kW. A single-phase arc welder would probably draw 10kW (but that’s a guess). My fridge draws 90W with the compressor running, which is quite good.

      One ZCell would provide enough power for me (3kW > 1.7kW + a bit more).

      One ZCell would ONLY JUST provide enough energy for my household for one day.

      Therefore, if I wanted 3 days of energy capacity, plus a buffer, I would need at least 4 ZCells, and I use 10kWh per day.

      The average household would need 3 days x 24kWh (consumption)/10kWh (ZCell capacity)v = 7.2ZCells. So AT LEAST 8 ZCells, as long as the household’s power demand never got above 3kW.

      Solar Panels

      A well-oriented 4.5kW PV system produces an average just over 19kWh/day throughout the year. If off-grid, you would have no limit for the number of PV panels, so it would depend on how quickly you want to charge and how much reserve you want.

      • Paul Holm says

        It would be more cost effective for of grid users to have 2 batteries and and small 1 kw generator. Generators are quite effective when running on full power and 1 kw is enough to fully charge batteries if running 24 hours per day.

        • regarding generators i have 2, 1 x 2 stroke that gives 7-8 hundred watts, bought for using small power tools where power is a problem 5 liters fuel uses about 1 liter per hr, & a 4 stroke 2200 w output uses about 1 lit p/h under load kinda noisy though that is still 25 lit p/day plus it wouldn’t last 24/7 for to long. we need something like a capacitor that works like a battery that is inexpensive or we might as well stay on grid & keep getting screwed by the power companies. unless a better storage system comes our way. so far every thing else just costs a ship load of $

      • Yes but if you have a zcell you must have solar , only use the batters at night a 5.5 kwh solar will make more than is need , after you are talking about the sun capital , Darwin

    • Richard Williams says

      The Z-Cell is impressive technology, not least for its ability to shut down for indefinite periods without losing capacity, but DON’T EXPECT TO USE IT OFFGRID.
      For over a year I tried to negotiate an offgrid system, but no supplier was interested. Finally I traced the issue back to Redflow itself, where I was told by Redflow’s chief technical officer that the company was unwilling to support offgrid installations unless TWO batteries were installed, for when the system has to be restarted after its regular maintenance shutdowns. Single battery systems offgrid would not be supported. That was despite being told that a 12V battery is sufficient to restart it after its regular maintenance shutdown, and despite my willingness to use a generator to re-start it if necessary.
      Their reluctance to support single cell offgrid systems is due to a belief that “the average customer/integrator is simply not mature enough”, which I take to mean that they have unrealistic expectations for their systems.
      They did at least suggest the use of lithium iron phosphate (LFP) batteries for their relative safety compared with other lithium batteries.

  3. Derrick Nalli says

    I enjoyed reading this article, found it very informative and written with some really honest descriptions and humor chucked in as well. We installed our system 6 years ago and still have another 4 years of the 48.5 cents per unit feed in tariff left. In another 4 years time who knows what developments will be available. Solar power with battery storage is the way to go.

  4. Hi Finn,
    Great as always.
    The bit which confuses me is amount of cycles and what formula its measured against. Example being if a company claim its good for 30,000 cycles. How is this monitored or recorded? Is the consumer able to access this info, just in case I end up being the poor bugger with the faulty one and its dead in 2 years and I need to make a claim.
    Then the question of what makes a whole cycle? I’ve been watching the fronius battery storage info online and they claim that if you use multiple small amounts of energy it equals one cycle as does if you use 50% twice.
    My point is, Does one cycle using 10kwh in Zcell, equal when you have used 10kwh of energy regardless if its only once or multiple times.?

    • Finn Peacock says

      Hi Thomas,

      Great question.

      The 30,000 number is for warranted kWh throughput. This is the equivalent of 10kWh of storage x 3,000 cycles The battery is controlled by a mini computer and connected to the internet. It logs everything and stores it in the cloud. Every kWh that is stored and discharged gets logged. Once it has logged 30,000kWh then the warranty is up. The warranty also expires after 10 years, whichever comes first.

      Just to be clear if you charge 1kWh and discharge 1kWh every day for 10 days, then you have used 10kWh of throughput, or one full cycle towards the 3,000, or 10kWh towards the 30,000.

      Hope That Helps,


      • Finn,
        Great article, thanks.
        Some questions without notice:
        – Is the data stored in the cloud accessible to the owner and downloadable?
        – Who owns the data?
        – Is the data used for system monitoring to allow for automatic fault diagnosis, degradation below warranted levels etc?
        – What happens to the warranty if there is no internet connection?
        – Is the electrode purge automated?
        Thanks again for your article and Q&As.

        • Finn Peacock says

          HI David,

          I asked Redflow and here’s their response:

          “The data is stored in the cloud, and yes the customer can access it, the customer can view the data via any http browser and view graphs of usage, consumption patterns and battery performance, at any time, and we actively encourage that.

          Ownership, of the data is something that I need to check, however we have no problem with customers having access to the data.

          The data is used for a number of things:

          Check that the battery is being operated according to spec, and so ensuring warranty conditions are being adhered to.

          It is used for proactive warnings, should the battery show signs of abnormal behaviour, we could ‘preempt’ a failure, or a warranty claim by ‘fixing’ or rectifying an issue early and it is used for diagnosing faults in the first instance, and working with the customer, on first level support issues

          If there is no Internet connection, the warranty will be shorter, this is outlined in the new warranty document, to be released shortly.

          Yes the ‘strip’ or electrode purge is automated, yet the customer has control over when this happens to that they are no inconvenienced if it is offline.”

          Hope That Helps,


          • Warranty is shortened if you don’t connect the battery to the internet? No thanks.

  5. Can the redflow battery be refurbished after the warranty period, for example by replacing the pumps and the cells.

    • Ronald Brakels says

      Diego, Redflow says the electrode stack can be replaced and the unit refurbished. I assume the pumps would need to be replaced, but the polyethylene tanks may have a very long lifespan. When used for water piping the material is expected to last for over 100 years.

  6. BarleySinger says

    I am still confused as to why nobody in Australia is making old fasioned Edison NiFe cells. They are far better than people relize. The electrolyte can be obtained as a soap making supply. You can’t hurt them with running them flat or overcharging them, which means you don’t have to dramaticaly oversize the bank. You can add more later without having to start with all fresh cells. They last for ages (there are 80 yeard old cells still in use). The materials are cheap.

    Right now the problem is all supply and unnecessarily high prices. You either pay an extreme cost to get them from the USA or buy Chinese knockoffs (and who knows how long they will last). We have a functional and inexpensive tech right now, and nobody seems interested, but then you can’t patent it! So that is probably why. Without changing the design, you can’t secure the right … and the old design is good.

    • Ronald Brakels says

      BarleySinger, while nickel-iron batteries are the most durable batteries around, they are not particularly suited for home energy storage. This is because while the batteries themselves are extremely tough and can last over a century, the electrolyte inside them is not so long lasting. For modern Chinese made nickel-iron batteries, I think it is optimistic to expect the electrolyte to last for 7-10 years before it needs to be changed under normal use, and replacing the electrolyte is a considerable expense.

      They also require regular maintenance as they need to frequently be topped up with distilled water and many people considering home energy storage these days aren’t interested in a battery system they have to maintain and prefer something they can, “fire and forget”.

      They are slow to charge and discharge, which is fine for some applications, but it hurts the economics of home energy storage, as it can potentially make it difficult to fully charge them during the day, and fully discharge them overnight or during peak times.

      And they’re not especially cheap compared to their main competition, which is be lead-acid batteries. Most, if not pretty much all, households are going to find lead-acid batteries overall cheaper to use per kilowatt-hour, which is why, with just a few exceptions, they were what was exclusively used for off-grid living until recently.

      • Hi Ronald, bump to your review here by mistake. Kudos for your good knowledge in technical and cost analysis (for various battery system). At last, another good quality writer in the midst of ‘crap’ noise these days.

        It is interesting to see how psychological effect plays part in consumer decision, i.e. bias towards the ‘desirability’ of a product (such as Tesla branded item), or preferences in the past (such as NiFe).

        Sometimes, superior product is not getting its fair attention due to this ill effect.

        • Firstly, I thank David also for his candid, informative, objective & jovial assessments of this emerging technology, particularly amid all the ‘noise’ & hype as you’ve mentioned.
          While the ‘noise’ of marketing does sometimes hide competing technologies, I think its important to acknowledge that sometimes a bit of hype & blatant self promotion is necessary, particularly when breaking new ground in the market. While Elon Musk is not adverse to blowing his own trumpet, it took someone of his audacity to successfully disrupt the car market with his Tesla brand, where many others had failed. He knew with his first Tesla model that he had to make electric cars ‘sexy’. If he’d entered the market with something resembling a science experiment he would’ve only succeeded in reinforcing in the public’s mind all its worst fears. & preconceived notions, of what electric cars were meant to be. He’s managed to take electric cars from being objects of derision to objects of desire, so effectively, we now have every major car manufacturer lining up to compete in a market he largely created. I’m not sure he would’ve got nearly 400 000 pre-orders & deposits for the Tesla Model 3 if it didn’t look & perform like an established Euro prestige marque.
          I think what he’s managed with the Powerwall is a similar achievement & if it means we end up with a highly competitive home energy storage market, then so be it. By making home energy storage ‘sexy’, he’s managed to attract customers to the market that may have otherwise ignored its potential. We’ve already seen competition in the market reduce the cost of storage by, I believe, about 30% last year, & Moody’s has estimated a further 50% fall within 3-5 years.
          Like you, I like to know the dollars & cents as well as the quality of the technologies on offer. I’m not yet convinced that Tesla’s product, or any other competing product, is the best fit for my needs as yet, but I’m very happy that the market forces at work are providing me with an increasing variety of options at a reducing level of cost. We haven’t quite gotten to the ‘Model T moment’ for electric cars & home energy storage just yet, but I think both are imminent.

      • Justin Ayers says

        Why isn’t it possible to produce a NiFe battery bank that self waters (capturing its evaporative emissions)? Or, at the very least, design a system with a water tank so people can add 10 gallons or so of distilled water all at once.

        Volume production likely accounts for the high cost. Is nickle really that expensive?

        How much does the electrolyte cost over a 10–20 year period?

        If there is enough capacity, wouldn’t that overcome the drawbacks you mentioned, in terms of discharge rate and such?

        If you haven’t done so already, please consider posting an analysis article about NiFe batteries. People are interested in this tech and there isn’t enough high-quality information.

  7. *slow clap* What an entertaining and informative article! You sir, are a legend!

  8. Awesome review. I’ve been looking for a technical review for the Z battery for some time. At last. Funny too!

  9. a very funny article but also very well researched. nice writing

  10. Steve Ritter says

    Hi Ronald – just wanted to add my comments to say ‘thanks for a great article’ – really well balanced and inclusive of the real world considerations to make an informed decision on storage selection.

    P.S. my calc’s for $ / kwh when factoring in 5% cost of capital is: $22,786.97 (principal + interest over 11 years) / 40000 = $0.57. You calculate $0.62.
    ” …. $17,500 divided by 40,000 kilowatt-hours comes to 43.75 cents a kilowatt-hour. If it is used at full capacity over 11 years, then including a 5% cost of capital, its total cost will come to 62 cents a kilowatt-hour.”

    • Ronald Brakels says

      Steve, thanks for your comment. Because battery systems give a payout of stored electricity each year it is not enough to divide the cost of a battery system plus interest over 11 years by total kilowatt-hours stored to get the cost per kilowatt-hour. Or at least, I don’t think it is. I have to admit I just put the figures into a spreadsheet and used the result it gave me. It is possible I used the wrong formula. If an accountant wants to tell me I am going about things the wrong way… well, I am willing learn. Slowly.

      (By the way, I can’t see how you got your result for principle + 11 year’s interest.)

  11. Steve Ritter says

    Hi Ronald, I just used the following calculator … which assumes financing of $17500 over 11 years (132 months) at 5% pa interest paid monthly. Yep I just took the total investment (ie: $22,786.97 which includes the cost of capital) and divided by 40000 kWh. To my mind this should be all that is needed … but I might be missing something.


    Cheers, Steve

  12. Tony Smith says

    Hopefully not a too stupid question ….

    Ok so we use it in an off grid application. So far so good.

    To avoid assumptions, off grid inverters need to be connected to the battery bank to stay alive. Disconnect the battery bank, they instantly turn into a boat anchor.

    Our Redflow Wunderkind happily does its things for 2 weeks and there is great rejoicing. The owner issues a smug warning to his off grid neighbours laughing derisively at their prehistoric lead acid systems.

    But then! Our redflow decides it’s time for its fortnightly shut down and purge. So it shuts down….

    Can you see where this is going yet?

    Our smug owner now has zero power for 2 hours. The off grid inverter died at the same time the redflow started its purge cycle. Once it’s dead, it can’t start a generator and as far as I can tell, nothing in the redflow did either.

    Now our redflow has zero power available to it because its killed the off grid inverter and the generator auto start function in one fell swoop.

    So where does our redflow get the power from to do its purge cycle? Remember it’s killed all potential sources of power…..

    As far as I can see it can’t do its purge because there is no longer any power anywhere.

    Maybe I’m missing something?

  13. Michael Hampshire says

    Ron, You are my new hero. Technical knowledge and a brilliant sense of humor.

    Potentianally useless question for you guys.
    Could or would you ever mix technologies ?
    i.e. would there be any advantage (or even possible) to have both a Z-Cell AND Tesla in the same setup to take advantage of the pro’s & cons of both systems.


    • Ronald Brakels says

      Michael, hybrid inverters and battery inverters can typically handle multiple units of the same battery, but I don’t think it would be possible to find one that could handle two different types of batteries at once. This means there would be the cost of an additional inverter and coordination issues. So I don’t think under any ordinary circumstances it would be worthwhile to mix storage technologies. But it is possible hybrid battery storage systems will become available in the future that combine two different storage technologies in one, such as the CSIRO Ultrabattery that combines a supercapacitor and a lead acid battery to get the advantages of both.

  14. This may be an uninformed naive question but Im going to ask it anyway.
    Lithium batteries used in cars degrade with time and the number of recharge cycles. I am wondering if the zinc bromide battery technologies would overcome this problem. Perhaps Tesla may not be aware of Redflow..
    However zinc bromide batteries may not be suitable for vehicles with issues like being in mobile and unstable situations that are not permanent or resting. Or enclosed and in higher heat situations. But could they be modified possibly in some way for this application ??

    • Finn Peacock says

      Hi John,

      The Redflow style batteries consist mostly of a big tank with 100s of litres of toxic liquid in it. They are not suitable for mobile applications because the liquid will slosh around and cause havoc with the pumping and plating processes.

      Maybe if the liquid could be made more like a gel it could work?



      • There are a few research designs of nano flow cell batteries that are believed to get around the sloshing effect by essentially making many of these types of cells at a miniature scale, and thereby spreading the liquid among many small tanks.

        Not sure if anything is realistic yet in terms of a car battery, but it’s being worked on.

  15. Stuart Walsh says

    I’d like to know why you think Redflow are better than Tesla, also how much fitted as I can now have a Tesla fitted for just under $10,000.00, also, I believe Tesla have a memory problem if power slips too low, does Redflow have this, or is it true that I’ve read somewhere it doesn’t.

    So, how much fitted is my main question.

    • Ronald Brakels says

      Stuart, I won’t say that the Redflow ZCell is better than the Tesla Powerwall. I will say they are different. I don’t recommend either at the moment for on-grid storage because they don’t currently pay for themselves and they aren’t environmentally beneficial. If people want to buy home battery storage I will give them the best information I have available to help them make a decision. But if someone is tossing up between a Powerwall and a ZCell I would recommend they try to get, in writing, detailed information on just what their warranties cover first.

      As for memory problems, all lithium-ion batteries need to maintain some level of charge to protect them from deteriorating. Exactly how much they need to retain depends on the type. Some are able to have a 95% depth of discharge with very little harm. Others shouldn’t be discharged more than 85%. This means they can’t be stored in a discharged state. The Redflow ZCell doesn’t have this problem. It can be fully discharged, left for years, and then started up again without deterioration in capacity.

      And if you want to know how much a Redflow Zcell costs installed. currently it is estimated to be $17,500 or more.

      Note that a $10,000 Powerwall installation may be one that limits it to 2.5 kilowatts of power and is unable to provide backup power during a blackout.

  16. Stuart Walsh says

    HI Ronald

    Thanks for that.

    The Tesla Powerwall has a 10 year warranty and it’s for the 6.5 kilowatts system Ronald. All installed and warrantied for 10 years and just under $10,000.00.


    • Ronald Brakels says

      Note the Powerwall’s capacity will fall. By just how much it not clear as its current warranty is not particularly forthcoming:


      Its original warranty covered it for the first of 2 years or 740 cycles at 85% of capacity which is a minimum of 5.44 kilowatt-hours. Then 4.6kWh per cycle for the the first of 3 years or 1087 cycles, then 3.8kWh per cycle for the first of 5 years or 2368 cycles.

      The Powerwall has a continuous power output of 3.3 kilowatts, but if it is AC coupled with a Sunny Boy Storage it will be limited to 2.5 kilowatts.

  17. Stuart Walsh says

    Hi Ronald

    One question is, is the Redflow coming down in price?

    Also, does the Redflow system have backup in a blackout, as I’ve been told the 6.5 k system can – Tesla Powercell that is.


    • Ronald Brakels says

      Lithium-ion batteries are coming down in price so if the Redflow ZCell wishes to remain competitive it will have to fall in price also.

      Whether or not battery storage can provide back up power in a blackout depends on how it is installed. Lower cost installations generally can’t provide power during a blackout while paying extra for a mulitmode inverter (also known as a hybrid inverter) can allow them to supply power when the grid is down.

  18. Stuart Walsh says

    Hi Ronald

    Well, I’m stumped then, which battery do I go for, as there are now sereveral on the market? I don’t know which one to get now.


    • Ronald Brakels says

      Well, the best battery will all depend on your goals. But if you are on-grid and looking to save money or benefit the environment, unfortunately home battery storage isn’t at a point where they will help you do that yet. You would be better off expanding your solar system or investing in energy efficiency.

      But if you want batteries because you are off-grid or for non-economic or non-environmental reasons, then our battery comparison table should be able to help you:


      It gives details of a wide range of battery systems and economic information such as warrantied cost per kilowatt-hour. It also has links if we have done a more in depth write up of the system.

      Hope this helps.

  19. Stuart Walsh says

    I have 19 solar panels, and want to decrease my electricity bills, so hope that answers what I want them for Ronald.

    That list is great, thanks for that, appreciate you time.



  20. If you are grid-connected, and are paid a feed-in tariff, batteries will make no difference whatsoever to your electricity bills. In fact, they will cost you money.

  21. Stuart Walsh says

    Hi Ronald

    Can I get your opinion on these please.

    Looking through the list in order of preference:

    1. Ampetus Energy Pod

    2, DCS PV

    3. ZCell


    • Ronald Brakels says

      Well, as you said you want to decrease you electricity bills, I assume you want to save money and I’m afraid that none of these will actually be able to save you money at the moment. It seems likely most people will cycle battery storage around once per day so you could look at the Cost per Total warranted kWh (1 cycle per day) row to see which once will enable you to lose the least amount of money per kilowatt-hour stored.

      As for other differences between them, two are lithium-ion batteries. These slowly decay over time even when not used so you’d want to be confident you would use them at fairly close to full capacity to limit your financial losses. The Redflow ZCell is a zinc bromide battery that doesn’t decay if it isn’t used and so can be left idle for extended periods of time without worry. A feature that’s useful for holiday homes or people whose energy consumption is particularly low for parts of the year.

  22. Stuart Walsh says

    Yes, but at $12,600 (which I take it doesn’t include installation) it’s bit expensive as of yet. At the rate they have been dropping lately, I haven’t seen the ZCell come down in price at all over the last couple of months the way others have.

    Can you give me a rough estimate as to cost of installation Ronald please, this may give me some clue as to what I am to expect to pay out overall. Yes, the ZCell is preferable, but price wise is an issue of sorts as electricians are becoming like plumbers in the way they charge. 🙂

  23. Stuart Walsh says

    Oh and your first sentence makes no sense to me at all, I’m afraid I’m a bit ignorant of such data and what it means.

  24. Stuart Walsh says

    I should read what you said before, derr, my mistake sorry. $17,500 odd.

  25. Jim Aitken says

    Thanks for the great reviews Ronald,

    Informative and easy to read and digest. I am about to build on an island in Vanuatu so need an off grid system and am trying to find all the info and comparisons I can as I am not solar educated so well done.
    Your good old fashioned humour tickled my fancy.
    Pity about your pumping problem!!


  26. Ronald,
    I find your articles very easy to digest and understand so if you could please help me with this annoying question I still don’t understand would be most appreciated.

    I have recently bought a Fronius 3 phase Symo Inverter for my 7.8Kw system with the intention that in a year or sooner I would add batteries.
    Now, I have always liked the ZCELL technology and approach and even though what’s inside is toxic, it feels safer than lithium to me.
    BUT I keep hearing that Zcell is low voltage and my inverter is high and the 2 shall never meet….. unless I add extra equipment which adds more expense and lesser efficiency so defeats the purpose.
    Is this 100% accurate?, as I thought the whole idea of hybrid inverters is that its a plug a play technology.
    Are we looking at the 80s again with HV and LV much the same as VHS and BETA technology.
    Just to make it more confusing, I read only today that ” The Conservation SA installation at 111 Franklin Street comprises two ZCell batteries connected via a 5kW Victron inverter. The 52 x 250-watt Tindo Solar photovoltaic panels on the building’s roof charge the ZCells through a Fronius solar inverter’

    which puzzles me even more.

    Many thanks and keep up the excellent articles


    • Ronald Brakels says

      Thanks for the kind words, Jascon.

      I’m afraid that, as far as I am aware, the Fronius Symo hybrid inverter is only compatible with the Fronius Solar Battery and the Tesla Powerwall, which are both higher voltage battery systems, while the Redflow ZCell is a lower 48 volt system. This means additional equipment will be needed to install a ZCell. This could be a battery-inverter such as the Sunny Boy Storage:

      Or it could be a DC converter such as a Goodwe GW2500-BP:


      With both the Sunny Boy Storage and the Goodwe GW2500-BP the ZCell will be limited to around 2.5 kilowatts of power rather than the 3 kilowatts of continuous power the Zcell is capable of.

      With the Conservation SA installation I am sure the Fronius inverter would be sending power to the Victron Inverter, which is an inverter/charger, and it would charge the ZCell with low voltage DC.

      I am sorry to have to tell you your Fronius inverter is not very flexible when it comes to adding storage. But on the bright side, the cost of what is required to retrofit a ZCell is falling and the field is developing rapidly. If you are looking to install a battery system in a year you’ll probably have more options then.

      Hope this helps.

  27. Hi guys,

    So how does the ZCell compare now to the recently released Powerwall 2? I know details on the PW 2 are still a bit fuzzy. Any immediate thoughts?

    • My immediate thoughts are that lithium-ion is worth considering again. I still might have to rule it out, because I’ve had 100% failure rate with small lithium-ion batteries in household appliances and devices. My main consideration needs to be the tropical environment where I live, which seems to cause trouble for many batteries of different types.

      For my photovoltaic energy storage, the front-runners are ZCell and Aquion at the moment.

  28. Bruce Hughes says

    Hello Ronald,
    Great reading, keeping me alert whilst on night shift. Have you found info on the Redflow ZCell cost of replacement Electrode Stack and fluid? If this is a fraction of the cost of a new unit one would have to consider this as a great selling point.
    I would like to think that people willing to spend $20k on battery storage would consider the cost involved after the first lot of batteries need replacing and use this in their reasoning to purchase a system.
    Bruce H
    Kleinton just north of Toowoomba

    • Ronald Brakels says

      Hi Bruce, it may be years before anyone needs to have their stack replaced and fluid cleaned or replaced, so I’m afraid I have no idea how much it might cost. But maybe Redflow will be able to give an estimate.

      • Colin Vincent says

        I can’t vouch for this, because I can’t find any such information directly from Redflow.
        I’m told that at the end of the “expected” lifetime of 10 years both the electrolyte and the electrode stack need to be replaced – at approximately 50% the cost of an entire replacement of the battery.
        Oth, according to Redflow, “The zinc-bromide electrolyte fluid isn’t expected to degrade with age.” https://faq.zcell.com/content/1/38/en-us/tell-me-about-end-of-life-_-is-zcell-recyclable.html
        I don’t have any idea about the electrode stack nor about any components that would warrant the “expected” lifetime being what it is.
        As it is, cost of electricity from Redflow compared to that from the grid makes it economically unviable. There seem to be better options on that score, but they all fail regarding efficiency and whatnot…

  29. Terrifically informative article, Ron. Do you know if Redflow has plans to pay something to buy back the battery at the end of its life or to offer a reduced price on a new system? In fact, do any of the current battery producers have such plans?


    • Ronald Brakels says

      Hi Agnes. I have not heard of any plans by Redflow to buy back their battery at the end of its life, although they do say it can be refurbished. I can’t think of any battery system manufacturers who have promised to take their systems back at the end of their lives, but I’m sure they exist. (It’s a big thing in Europe.) But for lead-acid batteries, there are recyclers in towns and cities willing to haul them away. They’ll even pay a few bucks for them.

  30. Hi Ron. Can you give some advice? (I’ve read as many articles here as i can before asking). I am completely off grid with 4kw of panels, SMA sunny boy 3000TL and SMA Sunny island 6OH. Currently i have 4 gels configured at 48V 200AH but they seem to be dying (now 6 years – other components 6months old only) because although they show 56% charged in the morning on the Sunny remote control, the voltage has dropped from 54V at its peak throughout the day to 33V overnight. I can still run lights and fridge and other low voltage items on this in the morning, but if I start the water pump (750w Davey – yep i understand through research about start up power vs continuous power) the sunny island shuts down due to “low voltage min” and i have to start the generator. Being that i have to get kiddies off to school every weekday morning (and can’t wait for the sun to boost the voltage) I suppose i have to look at new battery options. was keen to go with LG Chem 6.5 RESU and also looked at your review on ZCell, although its big and bulky and requires down time for maintenance + probably has vents in the cover that bastard mud wasps climb into and clog up – voiding my warranty. being that i am budget constrained, should i just go with more gels at $2000, and wait another 5 or more years when technology may offer something better and cheaper? I hear whispers of mobile phone batteries that charge in 15 seconds and last a week…..now if that could translate to home storage this “hill folk’ mum would be overjoyed!

    • Ronald Brakels says

      Because you are budget constrained, I’m guessing you probably can’t afford to take the chance of trying out some new lithium batteries, so I am thinking you may be much better off getting new lead-acids for now and then getting something better when they need to be replaced. For off-grid use, tried and true often beats new and shiny. (But if you do decide to go for lithium or other batteries, I’ll be glad to hear how they turn out for you.)

      • My advice would be:

        If your gels have fallen over after 6 years either they are flat plate or if they are good quality tubular you have an issue with chronic undercharging leading to sulphation.

        Assuming we have started with good quality batteries, then what you need is an auto start generator as priority 1.

        Then to your solar – you need an MPPT charger/regulator and the ratio of solar capacity to avarrage dauly kEH usage needs to be a minimum of 0.5. Example if you use 10kwh per day, you need a bare minimum of 5kw of solar (and an MPPT regulator). Some
        people say the ratio should be 1.5 i.e 10kwh of daily use = 15 kw of solar.

        Unless you’ve got all of the above, it won’t matter whether your batteries are lithium or pixie dust, they will die early.

        If you do have all the above, I’d suggest looking at LG Chem provided your loads are under 3kw contact (with an auto start generator and a Selectronic SP Pro)

        So in summary and in order of priority:

        1/ auto start generator (startable on SOC and on load)
        2/ Right size your solar
        3/ Buy good quality batteries. If Gel, only but tubular and especially carbon

        Fail to get all this right and even pixie dust batteries will die quickly.

  31. Now I may have nodded off when the mention of maximum input power (Current) was mentioned in class.
    If lead acid flooded cell do not appreciated over 10% of capacity as a maximum charge rate what is the ZCells specs on this?

    Answer – Maximum current 50 Amps at charger set rate of 57 Volts = 2850 Watts.

    So Two parallel strings of 15 panels at 24 volt 200 watt panels joined in series to produce 48 volt????

    • Ronald Brakels says

      Hi Brett. Batteries charge and discharge at around the same rate, so with the ability to discharge a continuous 3 kilowatts a ZCell should be able to charge at about the same rate and so 2,850 watts sounds about right. But I would charge it with an compatible multimode (hybrid) inverter, as the output of panels alone is going to be quite variable.

  32. Great review.
    Covered all the bases lucidly.

  33. As so many others have said, a really well written review.
    Has most of the answers so many don’t. Kudos++

    Apart from low maximum power and weekly 2 hour stoppage, it has many benefits.

    It is hard to comprehend why such a simple system has such a high cost, and I can only hope the price scales down with volume signficantly.

  34. Ron Horgan says

    Hi Ronald. I enjoyed your jocular style and sharp wit until I got down to your safety advice.
    I can’t find your CV and I don’t know if you have read the Redflow Safety Data Sheet ZBM2. If so you have missed some relevant information and your jocular advice requires some revision.
    “we shouldn’t fear the new”
    and “people have a bad habit of focusing on any potential negatives”
    is a rather cavalier attitude.
    “don’t drink zinc bromide” and its less dangerous if diluted with water etc.
    Zinc bromide is extremely dangerous as follows
    :H304 Harmful if swallowed ( extremely destructive to tissue etc)
    H314 Causes severe skin burns and eye damage.
    H341 Suspected of causing genetic defects.
    H400 Very toxic to aquatic life
    H 410 Toxic to aquatic life with long lasting consequences.
    There are 34 hazard notifications listed
    For transport the electrolyte is classified as dangerous goods when shipped in the uncharged batteries .
    However all of the above applies to the electrolyte in the uncharged state.
    Once the battery is charged elemental bromine is contained in a complexed oily solution. Bromine is a halogen of higher molecular weight than chlorine but sharing many similar properties. Chlorine dropped in barrel bombs is used as a war gas.
    I was surprised that batteries containing free bromine were approved for use in dwellings?
    In the event of a house fire the liberated bromine could cause widespread casualties. Does Redflow take responsibility for such damage claims?
    This is not a risk to be glossed over by jocular advice .
    The least that you should do is include the complete Safety Data Sheet on this evaluation so that potential purchasers may obtain expert advice as to the suitability of this product.
    The insurance implications are serious.

    • Despite the “jocular” tone I found this article more objective and informative than many pieces written by “reputable” experts. As accomplished professional, former scientist and avid ‘prepper’ I have and continue to spend a fair bit of time researching various aspects of self-sufficiency. They say that if you spend more 5000 hours researching a topicany you become a bit of an expert. I estimate I spent a lot more than that. The main skill I pride myself on gaining is probably the ability to smell a ‘bs’ risk analysis.

      Although I recognise the merits of the OHS philosophy and the great improvements to risk mitigation strategies in various aspects of our life, often there is the overzealous bordering on histrionic approach.

      For sake of objectivity we should look how this technology compares (in terms of risk) with existing technologies.
      Can you please post back to back the safety data sheet for led, sulphuric acid, lithium and all other “safe” chemicals from competing energy storage technologies. Or petrol and diesel stored for generators for that matter.
      Oh and maybe also a risk analysys for the behaviour of led and lithium batteries in a flood or bushfire situation and not forget hydrogen while we’re at it.

      And how does the risk or overall impact of a natural disaster or extended blackout compare in a community where there is widespread use of batteries (of various chemistry) with a community entirely relying on grid power. I would very much prefer to live in a community where there is a high density of ‘off grid’ capable homes, hospitals and other institutions despite the risk of being exposed to bromine (or led, sulphuric acid or lithium). Anything that encourages less dependence on the power grid (this technology included) is good news.
      Btw FEMA modelling shows that a severe, prolonged energy grid fail may lead to 90% casualities at 12 months. I think thats quite realistic.

      Let’s not completely disempower the prospective buyers by treating them like totally government dependent idiots and deny them all some responsibility for their decision making. ‘Caveat emptor’ should also apply to some extent to specialised purchases such as this.

  35. What leaves me really scratching my head about these Redflow flow batteries is that the current designs completely neuter one of the major benefits of flow batteries – that capacity can be increased (almost forever) by adding more volume of electrolyte.

    According to Redflow, you cannot add electrolyte storage tanks to the ZBM and it’s not designed to allow it.

    Seems like a major mistake right there.

    • Finn Peacock says

      You would have to add extra electrodes too – but good point – with the existing pump they could theoretically extend the storage and keep the same power.

  36. Did a lot to get down to the price. Not even in the market unless this has changed.

  37. loved all the articles please continue very informative

  38. Which inverter it would require? Is it off grid or Hybrid?

  39. Richard Williams says

    I live offgrid and have been quite interested in the advantages of the Z Cell despite its relatively high cost, but Redflow now advises it will not support offgrid installations without a second battery installed, despite the fact that relatively little power is needed to restart the system after a shutdown. This adds roughly $20,000 to the total system cost and therefore rules out the Z Cell for me, as I expect it would for most users living in the real world.

    So where to now? My energy needs are quite low, averaging 3.25 kWh per day. I have no heavy appliances, and can tolerate occasional outages. I am temporarily living in a steel shed waiting to build a house later this year. My car fridge is run by a 130AH lead acid battery charged by a single 140W solar panel. I also have a little 1kW generator to cater for other things such as TV, lights and computer, but when I move to the house I will need something more substantial.

    My house will be built underground, which will minimise the need for supplementary heating and cooling. For aesthetic reasons I plan to put the solar panels on the shed roof rather than the house, running AC power 100 metres from the shed to the house.

    i am aware of the battery testing project being conducted in Canberra by the Australian Renewable Energy Agency and ITP Renewables (http://www.itpau.com.au/technology/battery-storage/) and am leaning towards the Lithium Iron Phosphate (LFP) battery technology, though test results are still not conclusive.

    Is it possible for you to give me a nudge in the right direction, based on this outline?

    • Ronald Brakels says

      Hi Richard

      First off, I will mention there are plenty of people living off-grid who are replacing their old lead-acid batteries with new lead-acid batteries and not going for any of the new chemistries that are on offer. This is because they are comfortable with lead-acids, they know how to maintain and deal with them, and if one battery fails they generally have others they can get by on until they get a replacement. This isn’t what I would do if I was going to live off-grid, I’d try something new, but that’s me.

      I recently wrote about the results from the Battery Test Centre in Canberra:


      While lithium iron phosphate has a lot going for it, if you look at the graph for deterioration of their Phase 2 batteries you’ll see both the best and worst performer was lithium iron phosphate. So it’s a bit of a mixed bag. The Pylontech battery did very well, but it’s important to remember they are testing only a single battery and so it’s not possible to know how much part luck plays in either good or bad results.

      Our battery comparison table shows all the batteries we have information on that are available in Australia:


      Hope this helps.

    • Hi,

      I like your article and your concern about types of battery technology for solar off-grid storage, and I guess you are facing the same concerns as many others, including myself, when it comes to battery storage.
      Like most people, we all have to weigh up value for money when it comes to the expensive decision, one way or another.
      My biggest concern here, is that what you throw out, generally comes back to haunt you sometime in the future, weather it be lead, lithium, hazardous materials, or even the plastic bags and wrappings we throw out.
      The technology that I liked the most, was that of super capacitors, but like any new technology, there is always a but clause attached to it.
      A company called kilowattlabs at kilowattlabs.com have been working on these for some time now and are available for consumers to buy. I sent an email to them around a year ago asking for more information about their product, but received no reply. Since then they have dramatically updated their website and made their products available.
      I would expect like any other form of new storage technology, the cost of these will also be high. I also believe there is a but attached with this product as well, however; they also have a host of benefits.
      I have also had phone contact with Redflow who make the Zcell about their product and how they see their future, and I believe they will have to look and some form of product marketing strategy if they are to survive, as such, there share price has dropped dramatically, and I believe one of the directors has just resigned. What happens if purchase one of these batteries, and soon after, they cease to operate?
      With the ramp up of the electric vehicle, I was even hoping this would give rise to opportunities, as their battery capacity is very large, anywhere from say 50 to 90 kilowatt hours of storage depending on the vehicle. This would last for days, but would also take days to recharge if used for long periods.
      Again, they use lithium ion technology with a host of limitations, but after a few years, imagine picking up a used one of these that may only have a few dead cells in it for a couple hundred dollars. Good for people in my position with enough trade skills to repair them.
      To most likely answer your question, being off-grid doesn’t give much option, as you will most likely have to utilise some form of battery that comes with its environmental hazards, and if I were in your position, I am guessing that I would run with the lead-acid at this point, like others in this blog have suggested, as this may give you a time-frame in deciding on where you will go to next.
      Running the AC power from your shed will also be best for voltage drop purposes, even so, 100 metres will have some losses with AC as well.
      I also have posted the most recent comment, at this point on this blog site.

      Regards Colin

  40. A very interesting site with many very interesting questions and responses.
    One thing I have noticed is, that I don’t believe everyone has been calculating the ZCell requirements correctly. The specs say 3 kilowatts, however; the storage is 10-kilowatt hours, not 3. The 3 just relates to the maximum (peak) power that you can draw continuously at any one time, which I guess might not be enough for certain periods of the day depending on the demand, though it would deliver up to 5 kilowatts for those demands for up to 30 minutes (I am not sure what that duty cycle would be though).
    What is important from what I am reading here, is that you should be guaranteed to some extent up to 3650 100% DOD cycles. I could only imagine that you would only require as much as 50 100% DOD cycles in a year, and at worst 100. At 100, this would technically equate to 36.5 years before requiring a battery overhaul, and I would suspect that you would achieve a fair chunk of those years judging by the specs. Who knows what battery technology will be around then.
    It is fairly obvious that at this point that for many people, the cost of these batteries far outweigh the return benefits by feeding back into the grid, any surplus to help offset any electricity usage costs, though it is still not apparent which way the cost of electricity will go over time. Even if the electricity price comes down, I think it will be short lived, because as more and more demand is placed on the current infrastructure, eventually we are going to have to build more power stations for base-load power for commercial and industry requirements.
    Power stations are not cheap to build, and with coal being very unpopular these days and as time goes on, my bet is that the next one will be nuclear, just a guess. This being the case, electricity costs will have to go up again.
    Tesla use lithium-ion batteries for their powerwall battery (thousands of them connected to acquire the correct configuration), of which are going to create environmental problems of their own (something your children and grand-children will have the legacy of our bad choices).
    So, if unsure and want solar, stick to just running the surplus back into the grid until you are sure which way you want to go, and for many other rural Australians facing huge infrastructure costs to have electricity connected to their properties, I believe these batteries are a good call in combination with solar hot water, possibly gas for cooking, heating, on-demand hot water, and with back-up generator etc., so as to be able to be off-grid altogether. Besides, how could you go wrong with a 10-year Australian warranty on these batteries, and the environmental benefits that one day are going to be looked at more than purchase price.
    Kindest Regards

  41. Richard Williams says

    Redflow insists on installing two batteries to handle the restart after purging. This makes no sense, since a restart can be achieved (as your article points out) even with a hand crank, but they must have had a real problem with users who were unwilling to suffer even the slightest inconvenience. I spent much of last year trying to overcome their resistance, and made it clear to Redflow’s Technical Director that I was not at all worried about the occasional interruption and was quite capable of restarting the system with my generator if necessary, but that’s their policy and they’re sticking to it, which means that offgrid users will have to fork out almost $20,000 EXTRA to provide a second battery for this unnecessary redundancy. You would have to be stupidly rich, or just stupid, to do that. Pity, as the technology is great, but corporate policies must be obeyed.
    Also, note that Redflow has now opened its own manufacturing facility in Thailand, so you’re lighthearted comments about Mexico no longer apply.

    • Hi Richard,

      I like the research you have done, and like myself, I have learnt to heavily research everything that is of big investment cost prior to purchasing anything major.
      My biggest concern with Redflow, is not just the cost, or its redundancy issues, but the fact that as a public listed company, their share price has plummeted from 20 cents per share, to 0.086 cents per share as of today over the past 12 months alone.
      If this is the sentiment of the shareholders, what happens if the company continues to slide, and the then goes belly up? What happens to all the installations out there that may not have continued support?
      I am planning to install solar some time in March or April in 2019, and at this point I am going to consider just sending the excess back into the grid, as I believe that the battery technology is not going to evolve all that much until the electric vehicle becomes more dominant on our roads. I also intend to become CEC certified prior to this, and plan and design my own system, as I have electrical, electronic, and web development background that I hope to incorporate into the system design.
      As I mention in one of my earlier posts, getting hold of a used or slightly faulty electric vehicle battery would be worth experimenting with, if you were able to pick one up cheap enough, say $200 to $300, as many of them are in the range of 60 to 70 kilowatts. Only problem is the depth of discharge, as most use a massive array of 18650 lithium ion batteries, of which would be of the high quality high priced versions, and not some cheap imitation version coming out of China claiming ridiculously outlandish specifications.
      Thank you for the information you have posted, as I find it very helpful in understanding the batteries limitations, based on the direction the company has followed.
      Kindest Regards

  42. Laurence Smith says

    Very interesting, I have a 6.5 kw system and am thinking of adding battery

  43. Stephen Boyd says

    What a great and unbiased and humorous article, I just only come across this article, and the way you explained it not confusing at all, even I could understand it, and your sense of humour in your writing made it very enjoyable reading. Just a side note REDFLOW are now onto their 3 GENERATION product which they say will be up to 30% cheaper and ready by end of 2020. But please do your own research. Hope to read maybe a update on how they are doing since your last article.

  44. I have a Redflow battery (bought in 2017) and every third day is shuts down for maintenance for much more than 2 hours as indicated, I would say more like 13 or 14 hours. The company suggested that have the wrong inverter but it was installed by their approved installer at the time. The battery charge needs to go to zero to enable the purge to occur and evidently my inverter a Goodwe wont allow that to happens hence hampering the battery’s operation.

    The company has also suggested i replace the inverter with a Victron one. Mind you that will cost around $4500 installed.

    Any ideas?

    • Ronald Brakels says

      You paid for a battery system that has a purge cycle of 2 hours and not 13 or 14 hours and the people you gave money to in return for that have a responsibility to provide it. According to Australian Consumer Guarantees:

      “Products must match descriptions made by the salesperson, on packaging and labels, and in promotions or advertising.”

      You can find information on Australian Consumer Guarantees here:


      According to my understanding, you are entitled to a repair, replacement, or refund. If the installer can’t or won’t get the battery to function as you were told it would you can contact consumer affairs in your state and they should be able to help you.

      • Greg Flint says

        That’s what I was thinking, too. IF it turns out to be necessary to use a different inverter/charger, it would seem to be a fair arrangement to at least split the cost with Redflow.

        • I rang Consumer Affairs some time ago and all thye suggested was that I go to VCAT They evidently do not take any action only provide advice. Not much use at all. The company that installed the system no longer operates which I think is complicating matters.

          I will email Redflow once again

          • Greg Flint says

            I’d be interested to hear what happens.

            I’m in the process of buying and installing a minimum of 3 Redflow cells, and for that reason I’d like to know if the company responsive or not when it comes to support.

  45. richard williams says

    For anyone else out there living off grid, you should be aware that Redflow will not install single battery systems. I went through this with them two years ago, and they were unable to find any installers willing to support systems of less than two cells. So if you think $17,500 to $19,500 is steep, try re-running your calculations on double that!

  46. I have been very interested in these batteries for a long time.
    I have found that contacting Redflow directly to get answers is an exercise in frustration. I have also found that the Victorian recommended Redflow installation provider is not really interested in domestic dual battery systems. He just quickly brushed me off saying that it is not compatible with my Fronius Gen 24 inverter. So another dead end.

    Now I understand that the Z-Cell has a nominal 48 volt terminal voltage and Fronius has a higher input voltage requirement perhaps something >90 volts.

    So does that make it impossible to uses two Z-cells?
    Can two Z-cells in a series configuration (nominal 96 volts) then operate the inverter? The answer might be “No” due to the down-time requirement for the cell to rejuvenate?
    Again, if “No” then can it be solved by using a separate inverter to then interconnect the batteries into the Fronius Gen 24 when the sun is taking a nap? I am just finding it hard to get a handle on why?

    I really appreciate this site for getting real factual details.
    I like all of the features associate with Zinc Bromine so want to go that way if at all possible.

    • Anthony Bennett says

      Hi Piet,

      Gen 24 is not a goer. You need a Victron inverter for 48v nominal Redflow. They’re not currently approved as a grid hybrid inverter though.

      Selectronic SpPro (brilliant device) have been used in the past, they’re approved a grid connect hybrid, but I’m unsure why as a company they fell out of love with Redflow.

      Maybe a CET or Deye inverter would work? Or you could try talking to Craig Hunter at Xess?

      The trick is Redflow needs to have an extra layer of control, because after stripping, the cell needs precisely 17 volts (for memory) applied to kind of teach it how to be a battery again before resuming full charging current.

      They’re an interesting device. I’ve swapped them over for the owner of Redflow on his own house, (235kg monolith isn’t something that belongs on a 1.2 metre shelf) but as you’ve found not really a domestic market machine at the moment.

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