The Tesla Powerwall 2: Batteries Can Finally Pay For Themselves

Elon Musk proclaims the coronation of Powerwall 2.0

Elon Musk proclaims the coronation of Powerwall 2.0

Today at 12:15 Eastern Standard Time, Elon Musk announced the arrival of the Tesla Powerwall 2.

Some people were enthusiastically looking forward to this announcement, but I was not. I fully expected to be underwhelmed, and as soon as Musk finished his two or three sentences on the actual system, I felt a near fatal lack of enthusiasm sweeping over me.

From what Musk said, it appeared to simply be two original Powerwalls glued together inside a plastic case.

I almost died from lack of interest.  Fortunately, I had the foresight to have a hypodermic full of adrenaline at the ready, which I was able to jab into my heart and save the Coroner from having to write “Tesla induced ennui” on my death certificate.

Because it appeared to just be two normal Powerwalls attempting to make a baby inside a refrigerator, I assumed today’s announcement was the same as the original Powerwall launch. That is, all hat and very little cattle. Or perhaps I should I say, all Tony Stark and very little Ironman?


“Well, I got this costume from Nick Fury and I don’t think he likes me very much. What’s your excuse for having a target in the centre of your chest?”

But then, an hour or so later, the technical details became available on the Australian Tesla site and I found myself actually becoming interested. It turns out that Elon Musk had left out all the important shit. It appears that the Powerwall 2 is not simply two original Powerwalls glued together, but a fundamental redesign.  In fact, I became so very interested, I became excited. I almost had to take a Bex and have a nice lie down to counteract the effects of the adrenaline.

It turns out that it has a built in inverter and according to Tesla the 14 kilowatt-hour Powerwall 2 could be installed for under AUD $10,000.1

31 October Update: Tesla advise that the costs on the website do not include GST but are otherwise correct retail pricing for Australia.  

Now that is a major change.  If the estimated cost of installation that Tesla gave is correct, it means that, under a limited set of circumstances, battery storage could finally pay for itself for a limited number of Australians.

The Powerwall 2 Tech Specs

Here are the Powerwall 2 technical specifications I nabbed right off the Tesla Australia website:

Powerwall 2 technical details.

Powerwall 2 technical details. (Image credit: Tesla)

Update (4th Nov):  On Tesla’s American website the weight of the Powerwall 2 is now given as 120kg.  

It Has A Built In Inverter!

The most interesting thing about the Powerwall 2, which Elon Musk completely failed to mention, is that it has an inverter built into it.  I had heard rumors that it would, but I didn’t believe them on account of how it would be useful.

This is big news.  It means there is no need to go through the expense of buying a multimode inverter or other device to install it and it makes installation quicker and easier and therefore cheaper.

Why Musk didn’t mention this, I don’t know.  Maybe he is paid by the word and the board of directors decided they couldn’t afford to having him mention it or perhaps he is terrified of public speaking and every word is agony for him.

Battery Capacity

With 13.5 kilowatt-hours of usable storage, the Powerwall 2 has over twice the capacity of the original, which could store 6.4 kilowatt-hours when new.

It’s Too Much For Most Aussie Households Right Now

The high storage capacity of the Powerwall 2 will make it difficult for most households to use it all in an evening.  The average Sydney household without gas uses an average of around 17.6 kilowatt-hours a day and perhaps half that overnight.  This means only very large or very wasteful households are likely to be able to use a Powerwall 2 at full capacity for ‘solar shifting’ and so get the best possible return on the battery system.

Where the extra capacity may come in useful is to stretch out how many hours you can run in backup mode. Might be handy if any of those wind turbines conspire to blow down electricity transmission towers again.

And when Elon Musk’s master plan is complete and everyone has an electric car, the extra capacity might be useful too.

But bear in mind that being a lithium-ion battery, that capacity will soon start to diminish.  After 10 years it might be down to 70% or less.


Elon Musk said that, compared to the original, the Powerwall 2 has:

“More than twice as much power.”

It does not.  The specs show that the Powerwall 2 is able to provide 5 kilowatts of continuous power, 7kW peak. The original Powerwall was 3.3 continuous, 5kW peak. The Powerwall 2 has 50% more continuous power than the original. This is surprisingly low considering it has twice the storage capacity.

In his announcement Musk said 7 kilowatts, but that is misleading because it is the peak power which might only be for a second or two. He appears to be mistakenly comparing the peak power of the Powerwall 2 with the continuous power of the original Powerwall. And that’s misleading.

Additional Misleading Statement!

Elon Musk said:

“You can take a four bedroom house and you can have, er, you can power the, your fridge, the sockets, and lights, ah, for a day.”

This statement is misleading because many people will, quite reasonably, conclude he is saying an entire typical large home can be completely run off a Powerwall 2 for a full 24 hours.  This is not true because the average Australian and American house uses more than 13.5 kilowatt-hours in a day.  Most people won’t realize that, “…your fridge, the sockets, and lights…” does not include air conditioning, heating, hot water systems, or stoves, all of which are big users of electricity.

If Elon Musk were a salesperson in Australia you could argue that he just claimed the product was suitable for a purpose that it is not.  And under Australian Consumer Law, you could be entitled to a refund 2.

Inverter Size

Because the Powerwall 2 can provide a continuous 5 kilowatts, we know the inverter must be 5 kilowatts or more in size.  Because its peak power is 7 kilowatts perhaps that means the inverter capacity is the same, but that might actually be the peak capacity of the inverter and its actual rated capacity could be less.  So all I can say for now is it’s 5 kilowatts or more.

Update (31 Oct): Tesla have advised that my assumptions about the inverter are wrong – and that they’ll disclose the full inverter spec ‘shortly’. The tension is killing me.

Size, Weight, And Style

The Powerwall 2 is 115cm tall, 75.5cm wide, and only 15.5 centimeters deep.  But the bracket that holds it to the wall may mean its depth is effectively greater than that.  It is significantly smaller than the original despite having more than twice the usable capacity.

At 110kg it is only 10% heavier than the original.  This comes to 8.15 kilograms per kilowatt-hour, which beats the LG Chem’s RESU10 at 8.52kg/kWh.

Update (4th Nov):  On Tesla’s American website the weight of the Powerwall 2 is now given as 120kg.  The figures below have been adjusted to account for this.

Update (31 Oct): Tesla have advised that the Powerwall 2 has AC coupling built in. They say a fair comparison would include the DC coupled LG Resu’s weight + an AC Inverter’s weight. Fair call. The Solax SK-SU5000E Hybrid Inverter weighs 23kg, LG RESU10 weighs 75kg, total weight = 98kg. 98kg/8.8kWh = 11.14kg/kWh for the RESU+Inverter compared to 8.89 for the Tesla unit3.

As for the new design, its design is quite simple – a large, flat rectangle.  I’m glad they didn’t keep their original design because to me that always looked like a coffin with the word TESLA stamped on it.  While I’ve got nothing against Nikola, the thought of his ghostly remains powering my house always struck me as a bit creepy.  

Indoors, Outdoors, On-Grid, Off-Grid

According to the limited information Tesla has provided, it appears the Powerwall 2 can be installed indoors or outdoors, on the ground or on a wall.  When on-grid it can provide back up power during a blackout and is suitable for use off-grid.  If all this is true, it makes it a very flexible system.


The warranty is for 10 years and that’s all I can tell you at this point.  I have no idea if it will be similar to the weird one the current Powerwall has, which says it doesn’t cover batteries that suffer normal degradation but doesn’t define what that is.

Because the power output of the Powerwall 2 is lower per kilowatt-hour of storage than the original, that will have a beneficial effect on the lifespan of the batteries and so its warranty may be considerably better.

Battery Deterioration

Lithium-ion batteries decay with use and over time even when not used.  Based on the warranty of the original Powerwall when first released, I would roughly estimate that if the Powerwall 2 is cycled once per day, then it may retain 70% of its original capacity by the time it reaches the end of its 10 year warranty.  It could be more, it could be less.  The only certain thing is it will decrease.  There is nothing that can stop that.


The price of the Powerwall 2 is where it gets interesting.  I want to be very clear about the source of the figures I am going to give you, so I stole this image from Tesla’s Australian website:

A screen capture of the Tesla Powerwall 2 price from Tesla's Australian website.

A screen capture of the Tesla Powerwall 2 price and installation estimate from Tesla’s Australian website. (Image credit: Tesla)

So, as you can see, I didn’t pull these figures out of my ass.  I pulled them out of Tesla’s shiny ass.

Update (31st Oct): It turns out that Tesla’s shiny ass4 has gotten its figures wrong.  I have been contacted by Tesla (the company, not the ghost) who have told me the price they gave doesn’t include GST.  This means the price of the Powerwall 2 including GST is $8,800.  Their estimate for the cost of installation also didn’t include GST, so that will come to $1,595.  So according to Tesla, the total cost of an installed Powerall 2 will be $10,395.  At the time I am writing this, they still haven’t corrected their Australian website.

This makes everything 10% worse.  I have gone through my calculations below and adjusted them to take the correction into account.  I haven’t removed the “Yeah, baby, yeah!” video clip, so please just imagine that Austin Powers is saying it 10% less enthusiastically.

Tesla says the Powerwall 2 could be fully installed for roughly the same cost as an original Powerwall.  If Tesla’s estimate of $10,395 is correct, they have halved the installed cost per kilowatt-hour.  This means Tesla has finally done it!  After all this time they have finally managed to produce a battery system for around the same cost per stored kilowatt-hour as they implied the original Powerwall would cost!  And here I was thinking Tesla was full of shit and would remain full of shit forever more.  But it turns out they just needed a little time to work their way up to actually doing what they said they would.

The cost of the Powerwall 2 in America is $5,500 US.  This means, at the current exchange rate and accounting for GST, Australians are being charged $839 more.  Possibly as revenge for all the horrible, nasty, true things I’ve said about the Powerwall in the past.  After all, it doesn’t cost that much to ship 110kg over from California and hedging against currency fluctuations doesn’t either.

Does It Pay For Itself?

Does the Tesla Powerwall 2 pay for itself?

Step 1:  Imagine I’ve put a whole list of caveats here.  Enough caveats to build an empire.

Step 2: Yes.

Oh yeah, Baby! It feels so good to have finally gotten to step two after all this time.  But I have to admit, I never thought it would be with a Tesla.  Not after it treated me so cruelly in the past by building up my expectations and then leaving me high and dry.  Perhaps I’ll feel dirty in the morning, but right now it feels good.

The Cost Per Kilowatt-Hour

To work out the total cost per kilowatt-hour of stored electricity for the Powerwall 2 we need to estimate how long it will last, how much its capacity will degrade, how much of its degraded capacity will be used on average, the total amount of stored electricity it will provide, how much feed-in tariff will be foregone by storing electricity instead of sending it into the grid, and the cost of capital.  All my estimates below are in today’s money, which saves me the trouble of having to adjust for inflation.

Estimated Lifetime

The Powerwall 2 has a 10 year warranty.  If it is fully cycled once per day and decays to 70% of its original capacity by the end of its 10 year warranty period, over that time it will have stored a total of around 41,900 kilowatt-hours5  If we divide Tesla’s estimate of its installed price by that amount it gives us 25 cents per kilowatt-hour.

But the Powerwall 2 is likely to keep functioning after it reaches the end of its warranty.  If I assume it works for 15 years and falls to 60% of its original usable capacity in that time, it will store a total of 59,171 kilowatt-hours.

Average Amount Of Capacity Used

Most people take holidays and go out in the evening every now and then, so even people with very large electricity consumption are unlikely to always use all the stored energy in a Powerwall 2.  If I assume they use an average of 90% of the battery’s usable capacity per day, then the total amount of stored electricity will come to 53,254 kilowatt-hours.  Dividing the estimated cost of installation by that amount gives a cost of 20 cents per stored kilowatt-hour.

Foregone Feed-In Tariff

If a family has a six cent solar feed-in tariff, with the Powerwall 2’s efficiency of 90%, each kilowatt-hour stored is going to cost around 7 cents in forgone feed-in tariff.  This brings the effective cost of stored electricity up to 27 cents a kilowatt-hour.

Cost Of Capital

If a Powerwall 2 is bought with money that is sitting in a bank earning a real return of just 1% a year, then the money lost by not having the $10,395 installation cost invested for 15 years comes to around 3 cents per stored kilowatt-hour, bringing the total cost of storage up to 30 cents a kilowatt-hour.

Where It May Pay For Itself

Looking at my electricity bill, I see in South Australia grid electricity is around 30 cents a kilowatt-hour.  This means that at a total cost of 30 cents per stored kilowatt-hour the Powerwall 2 can just break even.  But because the state’s average feed-in tariff is actually a couple of cents higher than the 6 cents I assumed above, it doesn’t really.  However, there is a battery subsidy available in Adelaide City and North Adelaide, so it is possible for the Tesla Powerwall 2 to pay for itself, or at least pay for itself with a subsidy, in those two locations.

In other states, such as Western Australia and NSW, people on time-of-use tariffs can pay 45 cents or more for grid electricity during peak periods.  Provided they can use a large portion of their stored electricity during these peak periods and also assuming the spread of battery storage doesn’t cause the cost of electricity during peak periods to fall too rapidly, then it is possible for it to pay for itself without subsidy.

A Whole List Of Caveats

So, provided the following eight conditions are met:

  1.  The Powerwall 2 lasts for 5 or more years beyond its 10 year warranty.
  2. It doesn’t decline in storage capacity too rapidly.
  3. The household is a large user of night time electricity.
  4. The Powerwall 2 is used at close to its full capacity.
  5. The cost of capital is extremely low.
  6. The household receives a subsidy or is on a time-of-use tariff with high peak rates.
  7. If the household is on a time-of-use tariff with high peak rates it can use a large portion of its stored electricity during peak periods.
  8. Tesla’s estimated total installed cost is correct.

Then the Powerwall 2 can pay for itself.

These conditions are only going to apply for a tiny portion of the population.  But if that tiny portion includes you, then go out and buy a Powerwall 2.  And be sure to buy me a grape or something with the money you save.

Just be aware that at this point in time you won’t be helping the environment by buying one.

Or alternatively, you could wait and see if the Powerwall 2 announcement causes the competition to lift their game and offer something better.  I have mentioned in the past that LG Chem does appear able to produce their battery storage at a much lower cost per kilowatt-hour than they sell them for…

When Can I Get One?

If you are sure you want a Tesla Powerwall 2 you can go to their Australian website and put down an 8% deposit right now.  Tesla says installations will begin in February 2017, but as to when you’d actually get one,  your guess is as good as mine.  Hopefully you won’t have to wait too long.  I presume they wouldn’t have made the announcement if they weren’t ready to roll.6


  1. Some Australian solar installers are claiming that Tesla has mistakenly put the US price on the Tesla Australia website, and that there is no way you will be able to buy one for $10,000 installed. I have spoken to Tesla Australia and they have confirmed that the pricing on their Australian website is the correct pricing for Australian consumers, but that there was a typo – and the prices do not include GST – so Powerwall2 costs $8,000 + GST, and Estimated cost including installation is $9,450 + GST. Total = $10,395 incl GST
  2. I predict that the ‘Implied Warranty’ provisions of Australian Consumer Law will be a looming nightmare for battery manufacturers selling in Australia. But that’s a whole other blog post coming next week.
  3. I don’t know if the Powerwall also includes a solar inverter, it may just include the battery inverter. We’ll find out this week according to Tesla. If they have managed to squeeze a solar inverter in there too, I’ll be mightily impressed and the competition will be worried.
  4. I should probably admit that I don’t actually have an ass.  Technically, Tonto 23 is a horse.
  5. I originally wrote 40,680 kilowatt-hours with a cost of 26 cents per kilowatt-hour, but I’m afraid I was in error and was slightly off.
  6. Tesla have just assured me that they will be available in Australia from Feb 2017, although a Tesla reseller I told this to fell off his chair laughing, saying he considered that wildly optimistic.
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. frenchbruce says

    Do I smell a rat here?…Anyway, thanks Ronald for an enthralling late night episode of the life and times of Tesla’s wall mounted whiz bang better than anyone elses power box. Perhaps the post script might be the piece de resistance( ‘cuse the pun).

  2. G’day Ron, thanks for the quick update. There is no doubt the latest announcement is a game changer and it will certainly be interesting to see how the competition responds. It will be equally interesting to see how wall street responds as Tesla’s stock price has been sitting at a precipice on the verge of a fall.

    In regards to the specs, well I went looking also and I found on the US site that the Warranty was ‘Unlimited cycles for 10 years’ at supposedly a ‘100% discharge’ rate (??). If this is correct then 100%discharge is highly divergent from the normal recommended operation for Lithium batteries. Hopefully the user can set DoD to improve battery health overtime. Also, I suspect Tesla will probably adopt a similar residual warranty capacity as LG where after 10 years they might only provide say a 2% payment of the original purchase price if the unit fails during the warranted period.

    In regards to the inverter, well we don’t know yet if it can be supplied as either a single or 3 phase unit depending upon one’s setup (I run 3 phase so I am extra keen to get the good oil on this). Whichever way, the inclusion of a relatively high spec’ed inverter will surely challenge the likes of Solar Edge and Fronius who’s inverter offerings have underpinned the original Powerwall. I wonder if the inverter has been fully designed in-house design or whether it is being supplied under license. Also, if I was to obtain 2 x PW2s …. cause we eat a lot of vegemite on toast here ? … then the Q that comes to immediately to mind is – will the second PW unit come with a redundant inverter or will it will be taken out resulting in a lower price for the second unit?

    Early days mate … and as big Mal has often said … we are certainly “living in exiting times” … Duh! ?

    • frenchbruce says

      There are just too many imponderables with this Powerwall #2 and for the suggestion that a 100% discharge is allowable flies in the face of well established discharge criteria for all current lithium batteries and I don’t believe for one moment that Elon has come up with a new mixture.

      • Ronald Brakels says

        I am pretty sure the 100% depth of discharge Tesla has stated on their site is 100% depth of discharge of the usable 13.5 kilowatt-hours of storage and not the battery’s entire capacity. In his announcement, Musk described it as a 14 kilowatt-hour battery. We’ll probably have to wait to learn the truth about it.

        • Yes, I suspect you might be right here Ron. Nevertheless, it will be interesting to see if the DoD is user configurable as 13.5KWh still only represents ~ 4% margin. Given established wisdom, and if the unit was configurable, then I would probably err on the side of caution and have a DOD of at least 15%, reducing available consumption to approximately 11.9KWh.

    • Oppps … damn autocorrect on my phone. My usage of big Mal T’s words should have read ‘exciting times’ … not ‘exiting times’ as appears above. But then … maybe it was my Freudian Slip at play … channelling my pent up frustration of high electrickery prices and a prospective ‘exit’ from the grid itself once I have a reasonable Solar and storage solution. 🙂

  3. The 7kW peak may be the inverter output power. The US version of the SolarEdge inverter offered ~7kW from solar, but battery input was limited to 3.3kW.
    Even so, if the battery output is 5kW continuous, and capacity is 13.8kWh, that’s a ratio of 5kW/13.8kWh = 0.36, compared to the former 3.3kW/6.4kWh = 0.51. Potential rate of income is lower.
    From the manufactured cell cost point of view, the reduced rate allows for fewer cells for the same aggregate stored energy, to the same end of life.

  4. The loss of opportunity cost for the $9,450.00 invested at the CSB current TD rate 1.90% APR capitalised every 3 months for 15 years is $3,048.00 or approximately $203 per annum. So the cost of the power given that you are not drawing it from the grid is ($203 / kWH PA). So if the system was delivering 5 kWH per day then the cost of the power would be 0.11c kWH [loss of opportunity cost of the TD]. This calculation is based on the $9,450 being fully expensed and depreciated on day 1 of the installation. For the average domestic consumer it is not about payback but more about reducing or at the very least containing the on going cost of energy. If you purchase a car to get you to work [not employment related – tax adjusted] there is no payback calculation it just comes at a cost but you might be saving money on public transport.

    • Ronald Brakels says

      I have assumed the cost of capital to be 1% after inflation. It’s a very simple and low assumption. I’ve also assumed the cost of electricity will remain more or less constant after adjusting for inflation which is my default position until I get my crystal ball cleaned. I haven’t tried to put a value on having insurance against grid electricity price increases. One thing I perhaps should have tried to estimate is the value of having back up power during a blackout.

      • Jack Wallace says

        Come on Ron…..There are far too many unguessable variables (including a time parameter) involved to make assumptions like that.
        Moreover, you’ve ignored the cost of the iniquitous service to property charge which history clearly demonstrates goes up at a MUCH faster rate than either inflation OR the price of electricity. (and will probably accelerate as more and more people dump the grid altogether.)

        Finally, I don’t know how you’d go about calculating the “value of having back up power during a blackout”, but would suggest that a once or twice a year event of (maybe) one day’s duration would best be dealt with with a $500 generator (preferably LPG-operated.

        • Ronald Brakels says

          If you are indifferent between the back up services provided by a Powerwall 2 and a $500 generator plus $10 fuel a year, then assuming the generator’s lifespan is 15 years and using the same extremely low capital cost as I used for the Powerwall 2, the value of backup services would come to 0.0137 cents per stored kilowatt-hour. This would lower the cost of storage from 28 cents a kilowatt-hour to 28 cents a kilowatt-hour after rounding.

          • Don’t follow your arithmetic. However, it’s a fallacy to “assume” a lifespan of 15 years, since said generator might only be used for a couple of days per year. That would give it a lifespan perhaps greater than yours. In any case, a stand-by generator can be bought for under $500. Or, if you’re ‘handy’, built for under $100….. Moreover, there are other options of all sorts. Finally, my favourite solution is STILL a stand-alone solar (and/or wind/and-or hyrdo) system . I recently posted prices for deep-cycle agm batteries with a FIVE-YEAR WARRANTY for under $150 per kWh. (which post I can’t find just now…. but there are plenty of variations on a theme available.

    • Ant.. above provides an interesting analysis on payback. As an Economist with an electronics engineering background, I am of the opinion that the cost of solar/storage might represent a different value proposition depending upon who you are.

      As an example, an not discounting the environmental and feel good value one might get from saving the planet, I often look at my consumption cost as a grossed up value once I take my income tax rate into account … i.e. channelling the old axiom that my father would often say that “a penny saved is two pennies earned” … an axiom that is often attributed to Benjamin Franklin; but an axiom that most definitely pre-dates BF by many decades at least.

      In Australia, the average punter is taxed at 32.5 cents in the dollar between $37,000-$87K, so $100 of disposable income spent on an electricity bill is actually $132.50 in pre-taxed dollars earned in this circumstance. But then, the value proposition improves above $87,000 with a tax rate of 37cents in the dollar, and again above $180K where it jumps to 45cents (ouch!). In Australia, if the individual can reduce ongoing expenditure from an upfront fixed cost for a solar/storage system, then they might be able to then redirect pre-tax dollars saved into another tax effective earning vehicle (e.g. superannuation at say an earnings rate of 6-7% on average), then they increase their value proposition by a significant amount. This type of thinking typically evades the average analysis on payback and so I would encourage people to think about this in make a valued judgement about the acquisition of solar products/systems.

      • Finn Peacock says

        Great point. I’ve never thought about it like that. I try not to think too hard about anything involving taxes.

        • The next elephant in the room is Age Pensions about to change on the 1st January 2017. Especially those who’s assessable assets exceed $375,000 [couple]. My understanding is that for every $1,000 over that maximum you loose $3.00 a fortnight in pension. So if you was to convert $10,000 of cash into home improvements then the value of that investment is worth $780 per annum in pensions entitlements. This becomes just another variable that supports the efficacy of transitioning to PV + Storage.

          • Ronald Brakels says

            My friend just recently used that reason to convince her pensioner parents to install solar. As pensioners are generally at home during the day to self consume the electricity they generate, going solar is generally the best investment those with a roof can make.

      • Very nice I wish I had written it thanks for your support. Sometimes it is nice to have confirmation that you are beating a recognisable tune on a multi faceted drum.

  5. Howard Patrick says

    Thanks for another great article. As you have pointed out the comparison between the cost of home storage batteries to the KWh cost of batteries in EV indicates the likelihood of very substantial price reductions in the not too distant future.

    One of the many battery technology companies that might bring those costs/prices down is 24M. A read of a recent press release and their website might be of interest to some of your many readers.

  6. The good news is that Tesla are only just at the start of their cost reduction curve. Their gigafactory is way off final spec and Telsa is still in a position to release the Powerwall 2.0 at a price where it is competitive with the grid. 2020 has often been mentioned as the year where batteries will be as common as solar panels and This announcement confirms that 2020 may be conservative

  7. Jack Wallace says

    ‘..over and over and over again……’ as the old song goes.

    Won’t go into detail/arithmetic again, only repeat that lead-acid batteries can do everything the ‘Tesla-wall’ can: can do it (probably) far more reliably and do it for a fraction of the cost.
    A built-in inverter is an idiotic concept in principle ~for half a dozen reasons I’ve mentioned before: all your eggs in one basket, etc. etc..
    And finally the biggest bugbear from my point of view is that it cannot practicably be used unless it’s connected to the grid. So not only does one pay a lot of money for technology so complicated he has no control over it, but is STILL at the mercy of the grid-power establishment. WTF IS one paying for??
    And on that point I’d I’d seriously query the intelligence of anyone who’d pay an idiotic (read ‘any’) price for installation where the previously-mentioned Half-Witted-Chimpanzee can install a LA battery bank in under an hour…and then replace any component parts that may become unserviceable in minutes.
    Picture your Tesla-wall ceasing to work at, say, 9am on Sunday??

    • You failed to mention that work done by a unqualified half witted chimpanzee could void your insurance.

      • Chanced upon your comment at this late date. I’ve always contended that if one is halfway competent (and stays within his areas of competence) one doesn’t NEED insurance. The world I grew up in insisted one gain a general knowledge about just about everything (and had friends he could turn to to fill any gaps), and then took responsibility for one’s activities. (Mind you, that was in the day when the myriad of uber-regulation hadn’t been installed, and even an uneducated person could build a useful house for a year’s basic wage ~ again, with all the neighbours pitching in. About 4 million post-war refugee/migrants brought to Oz (“to build the country” ~ Menzies) did just about that. often in their spare time with whatever money they had left over from their weekly pay.
        I don’t know of a single one of them that didn’t succeed; some spectacularly so.

    • Jack Wallace says

      ps…The same argument applies to the oversized (to cater to any load) and overcomplicated ~ and doubtless overpriced inverter set-up.
      Long experience has convinced me of the value of the KISS principle in solar systems and just about everything else in life.
      In re. inverters a collection of smaller (and much cheaper!) inverters, each running a different circuit ~ and sized to suit THAT particular circuit ~ is the way to go. eg. Your fridge runs at 100w, you put , say, a 350w inverter (to account for ‘surge’) into the circuit. If you run two fridges stick a timer ($10 at Bunnings) inline and have the one inverter running both fridges ONE AT A TIME. If something goes wrong (Murphy’s Law) then you only have one circuit drop out: and at worst have to replace one small inverter.($148 from memory.)
      Though I usually wouldn’t tout a commercial product, MeanWell offer a selection of inverters that have been operating at my place on that basis since 2009 without ever a hitch. (Though I do carry a spare 700w one in case something does ‘hitch’.

      What do you do if ANY PART of the Teslawall ‘system’ goes down??

      • Encouraging unqualified persons to put themselves at risk is not good or appropiate advise

        • Jack Wallace says

          ….er, sort of like not letting school-children cross the road in case some driver loses control?. It’s virtually impossible to get into trouble with 12VDC. in my lengthy experience.

        • Incidentally:- Taking an endless ‘risk’ is the ONLY reason we’re here after 4 billion years of evolution. Imagine if your earliest ancestor hadn’t taken the (probably many) risks in coming down from the trees and walking around on only TWO feet! (and developing a keen eyesight at the same time with which to spot the sabre-tooth tigers lurking in the shrubbery.)

          As someone or other pointed out:- Behold the turtle. He makes progress only when he sticks his neck out. –

  8. not sure if your comment about weird warranty still holds true. seems like there is an updated warranty.

    • Ronald Brakels says

      Thank you very much for that. Tesla has finally put some numbers back into their original Powerwall warranty. So for normal household use they promise it will have at least 60% of its original capacity at the end of its 10 year warranty. I expect there is an very good chance we’ll see something similar for the Powerwall 2, but hopefully they will improve on it.

  9. Erik Christiansen says

    Ronald Wrote: “If a family has a six cent feed-in tariff, with the Powerwall 2’s efficiency of 90%, each kilowatt-hour stored is going to cost around 7 cents in forgone feed-in tariff. This brings the effective cost of stored electricity up to 25 cents a kilowatt-hour.”

    How that holds for total energy production is something that I just don’t understand. If the family uses all its stored energy, then nothing is foregone, and the cost remains at 18 c/kwh. Taking the 17 kwh/day average consumption, and 14 kwh (declining to 10 kwh) storage capacity, an average family must consume 3 to 7 kwh/day during daylight hours, as a minimum. You can’t sell what you consume.

    Any surplus array energy, exported directly, will reduce costs, not increase them. Any surplus stored energy is best retained for the cloudy day coming tomorrow or the day after. Not flogging the battery will extend its useful life.

    It is the “Going Off-Grid” equation which will interest many electricity customers, nervous about remaining in a dwindling pool of ripped-off grid dependants. Roughly, $10k/10 yrs = $1k/yr, for 14 kwh/day storage (dwindling to 10 kwh/day). Add PV array, installation, and some bank interest, then deduct all electricity bills (including service/connection fees) for the final net cost.

    Once off grid, there’s no restriction on array size, so overdimensioning for winter is no issue.

    I’m still leaning toward lead-acid batteries, though. Lithium might be the go for an electric ATV, to tootle around the paddocks, though. (With a low gear for hauling a little trailer load of firewood.)

    • Ronald Brakels says

      Erik, think about what would happen if you had a 44 cent feed-in tariff, as some people still do.

      • Erik Christiansen says

        Those days are gone, although some electricity customers are still in the process of falling off the end of that conveyor. That unavailable historical anomaly is not relevant to the rest of us, or the future. It cannot form the basis for a general cost/benefit calculation, I suggest.

        Sorry, but your comment does not address the points I made.

        • Ronald Brakels says

          Erik, people with a 44 cent feed-in tariff have no financial incentive to use battery storage. If grid electricity costs them 25 cents a kilowatt-hour, then even if Harry Potter waves his wand and gives them a free magically 100% efficient battery, they will be 19 cents worse off for every kilowatt-hour of excess solar electricity they store for use at night. Even with a free magic battery, storing solar electricity will raise their electricity bill.

          If their feed-in tariff fell to 25 cents a kilowatt-hour then they would be indifferent to storing electricity. Whether they send a kilowatt-hour of excess solar electricity into the grid or store it for use at night doesn’t affect their electricity bill.

          If their feed-in tariff fell to 20 cents then each kilowatt-hour of excess solar electricity they store and use at night saves them 5 cents on their electricity bill. This isn’t much, but since their battery is free and magically 100% efficient, it makes sense to do it.

          If their feed-in tariff fell to 6 cents then each stored kilowatt-hour of excess solar electricity would save them 19 cents.

          And if they had no feed-in tariff at all then each kilowatt-hour of excess solar electricity they stored for use at night would save them 25 cents.

          So the lower the feed-in tariff, the more economically worthwhile storage becomes.

          • Like Erik said, those days are gone. There was news months back that people are going to lose those high feed in tariffs (in NSW at least), and that they’re all going to be brought in line with each other soon (to the 6-7 cent price). I imagine other states are likely to follow suit, so that comparison isn’t very useful.

  10. john nielsen says

    Hi Ronald, a very interesting article and a fantastic forum. I think 2020 might still hold true for the viability to quit the grid. Many things have to improve before then, particularly inverters. I might be a half-witted-chimpanzee but I am happy with my 36 kWh lead gel batteries, and I am with Jack Wallace and Erik Christiansen about the lead acid batteries. Yes, what happens when just one component in the built-in inverter of the PW2 fails? Will you be without power for how long? Why does it have to be built-in? All too complicated for this chimp.
    With all of my battery power, I am still not able to quit the grid. 4 split system air cons = about 22 kWh night time summer months here in NQ. That power comes from the grid. All other power consumption comes 24/7 from my separate PV system. Oh yes, I am excited about the PW2, but I am even more excited about my Lead Gel.
    John Nielsen, Silkwood

  11. The insurance for a power failure of any kind in our case is called a Generator. We live in FNQ and our house is wired to be feed either Grid or Generator power. It is quite reasonable to point out that with PV + Storage there should be some form of backup. We could of course discuss how that might be achieved. We thought a one time cost for a Honda 2.01i petrol engine generator at $1,800 did not represent an unreasonable premium to support the refrigerators and a small number of lights in the case we lost power from the Grid.

  12. All very exciting stuff but I have a few concerns. It seems to me that there will be a lot of disgruntled PW1 owners who feel used and taken advantage of. They were asked to jump in and splash their cash and now there is no info if the old PW1 and PW2 can work side by side. That leaves me to my next question, what about all the consumers who already have inverters < 5 yrs old who desire batteries but are happy with their inverter/ monitoring systems.
    This product would then only cater for people who are completely new to solar and missing a huge chunk of potential buyers who now will need to dump their old or very new inverters to get a PW2.
    Companies like Fronius and Solaredge/SMA must be thinking 'Yikes" unless there is a way and a bloody good reason to persuade people to hook their inverters, battery chargers up to the new PW2.

  13. I think everybody has a different need and a different point of view and for some of you to discount others ideas is short sited,
    I am on the 44c +6c = 50c FIT I figured that it was in my best interest to get a battery system and let my grid tie 2kw system fit help pay for it, by not using any of that power and maximising the fit paid.
    So in my case i got installed a complete additional separate off grid system it has changed some and was added to in the first three months and is now 7kw second hand solar, 8kw inverter 2x 4kw the second switches on as required, 20kwh second hand LiFePo4 battery, if our battery runs low and it does from time to time we switch back to grid. But after a year it is better than a third paid for and works great, there is more than one way to skin a cat, and many other posabilities to go off grid but it’s a good feeling and that’s worth something too. Like Elon says if you ain’t part of the solution you are part of the problem.

  14. Thanks for your interesting instalment. I agree one size does not fit all. A careful analysis allows for individuals making better informed decisions. Some subscribers promote the concept of payback as though it is some form of business deal. Personally I am more interested in a simple calculation return on investment ROI [PV savings divided by acquisition cost]. Most of the figures I have seen don’t necessarily include inflationary trends, pre tax value of the cash flow, tax, loss of opportunity cost, government subsidy [eligible applicants], pensioners cash holdings [asset assessment] and the like. For us it was a simple choice pay $3,176.20 without PV or 1,512.60 with PV. That produced a ROI based on the 5.75 kW system cost of $10,500 in the amount of $1,663.60 tax free savings which equates to 13.099% APR and payback 7.63 Years. So lets say the tax payable on the saved cashflow was 30.00% then the real value of the savings was $1,663.60 x 1.30 = $2,162.68 or a ROI of 20.59%.

  15. Loving this. . And what exciting times are coming. .drooling at the mouth to see large or huge numbers or all to go off grid.just the possibility of detaching from the corporate strangle hold everyone thinks they need. if it was introduced too soon the man would not survive.. the corporates also need time to adjust as it would not be allowed if the suckers were removed too quickly.. the roof tiles

    • The latest bit of gotcha are Seasonal Demand Charges [Offered as an plan option in Victoria]. It is where the Energy Supplier sample your maximum usage in a 30 minute time slice between the hours of 3:00 and 9:00 pm during a billing cycle and convert that to a kWH with a 1.5 kWH minimum. That value is then multiply a fixed $ and/or c’s amount to calculate a fixed daily charge and multiple by the number of days in the billing cycle. This is then added to the charge for grid usage and may well be in addition to other fixed charges like Meter and/or Supply Charges. If you have got sufficient storage to cover consumption during the sampling period then it is entirely possible to keep this cost to that calculated at the minimum 1.5 kWH rate. Tariffs are fast becoming as complicated as mobile phone plans. These energy tariff plans add another variable to the value of storage to take into consideration if you was to subscribe. There is a commentary about these types of plans elsewhere to which I am sure the administrator may post the address.

  16. How does the pay off change when you factor in a wholesale feed a la Reposit?

    I am happy to install a battery (any battery) at break even just to give the middle finger to utilities for being slow to adapt and/or pushing back against progress. Plus the after tax cash flow benefit noted above.

    • Ronald Brakels says

      I hope to have some information very soon on how much people can save by installing Reposit. I’ll write about it as soon as I get it. (Unless Tesla announces a Powerwall 3 and I have to write about that instead.)

      • Howard Patrick says


        When do think it might be possible to get energy direct from PV systems to the batteries of EVs – so the home storage batteries don’t have to go through unnecessary charge and discharge cycles. Perhaps capacitors can help do this?

        • Ronald Brakels says

          It seems logical that in the future the DC converter part of a home solar and battery system should be able to provide low voltage DC to an electric vehicle and so minimize losses. But I think it would take time for people to work out how that will be done and for standards to be arrived at. That said, with the cost of PV continuing to fall, the easiest solution may be to simply add an extra solar panel or two to compensate for the losses and just plug an electric vehicle into a standard power point. I admit it’s not a very elegant solution, but it may be an economical one.

        • Erik Christiansen says

          Howard Patrick asked: “When do think it might be possible to get energy direct from PV systems to the batteries of EVs – so the home storage batteries don’t have to go through unnecessary charge and discharge cycles.”

          “More than 2 years ago.” would have to be my answer. (Or “always could”. See last paragraph.) I have an MPPT60-2 from GSL Electronics (a local manufacturer), which charges my lighting batteries. It would be simple to add a two-way switch, an additional HRC fuse, and a 60 or 100A Anderson connector for plugging in that electric ATV I’d like to have. The MPPT60-2 battery charger auto-detects 12/24/48v batteries, so the lighting and EV banks could differ in voltage. I’ve always done my battery switching at night, when there’s no high charging current to switch, and would check with the manufacturer before trying it in daylight.

          GSL said they’re coming out with a newer model which will handle higher PV array voltages, but I do like a lower voltage array (ELV), so I can legally wire it myself. (Not well suited for a whole-house array, if high power.)

          If the existing system is not DC + battery-inverter, but rather a solar inverter, with or without battery storage, then it’s even simpler. Just plug a 240v several-kilowatt battery charger into the nearest 240 Vac GPO, and hook it up to the EV. PV power then goes straight to the EV, without involving other batteries. Now you’re accessing the entire PV array, which may be more than the 3.4 kW that an MPPT60-2 will deliver. It’s like any other immediate (unstored) consumption.

          • Howard Patrick says

            Thanks for the additional information Erik.

            It seems the technically challenged masses like me will see off the shelf systems that can directly charge their EVs in the not too distant future.

            Problem is all these advances in technology are a deterrent to acting now – looks like another deferral; this time to 2018-19.

          • What some individuals are saying is that they are going to wait for this or wait for that taking the decision before calculating the loss of opportunity cost for the period of waiting. It is not a difficult amount to calculate and I think that some might find the results surprising. Some of the issues to take into consideration is the loss of opportunity cost for a cash investment. The savings per annum in energy offset by Storage. Tax payable on the cash investment. Tax payable by an individual on the cash flow without PV or Storage [employment income]. Adjustments to an age pension based on an asset assessment [cash converted into a non asset]. On my reading of the recently published Centerlink correspondence with the subject matter ‘Rebalancing the Assets Test’ applicable to an age pension for every 1,000 over the threshold the pension will be reduced by $3.00 a fortnight. So for every 10,000 held in cash over the asset threshold not invested into PV and/or Storage the loss of pension would be upwards of $780 per annum.

  17. One of the best articles I have read in a while. Captivated me. Well done.

  18. Tesla have published this Australian url where you can order the Powerball 2 pay a deposit with delivery starting in January 2017 This is not an product endorsement by my good self rather posted for information purposes.

  19. It appears GST is already included in the quoted cost, with Tesla replacing the term VAT with GST on their website:

  20. The Powerwall 2 specs are a vague and shifting sand, but it appears there may be two versions.

    “Powerpack 2 (sic) is offered in two versions, AC and DC, to provide customers with the greatest flexibility whether they are installing new solar,
    have existing solar, or want to use Powerwall as a standalone product for backup or time of use. Powerwall costs $5,500 (DC Powerwall includes DC/DC converter and AC Powerwall includes DC/AC Tesla integrated inverter.)

    Solaredge have updated their inverters, and now include LG.
    It’s possible the the Powerwall 2 does not have PV input, since it’s not mentioned. The DC unit replaces the existing battery, and the AC unit, replaces the battery + SMA option?

    • Ronald Brakels says

      Athomas, the information I currently have from Tesla is the Powerwall 2 is AC coupled and cannot accept DC power from panels.

    • Howard Patrick says

      Powerwall 4 and its equivalents from the likes of LG, Mercedes-Benz, etc, etc, might well have the capacities to provide energy for the home, energy to top up the EV and even feed surplus into the grid when rates are favorable? A lot now depends on the outcomes of the many promising R&D projects and early stage commercialization of more advanced battery technology.

      Imagine the impact of a magnesium based battery with twice the storage capacity and half the cost – seems there are many possibilities on the horizon.

  21. Richy Thompson says

    Please go back and check the specs of Powerwall-1.
    I assume you got false numbers and therefore you make a false statement by comparing those numbers.
    I still can find these numbers: “2.0kW continuously – 3.3kW peak performance”.
    Having 2.0kW and 3.3kW in mind – Elon Musk made a TRUE statement with “More than twice as much power.”

    • Ronald Brakels says

      Perhaps someone with an original Powerwall can correct me if I’m wrong, but I am very sure the ones installed in Australia output 3.3 kilowatts of continuous power. Tesla did change its specs as it got closer to launch, so you may be looking at old information. (Maybe Elon was thinking of old information?)

      On the topic of changing specs, one interesting thing is, on the Tesla site it now says the Powerwall 2 is 14 kilowatt-hours.

  22. Originally, the PW1 was 2kW/3.3kW
    Musk said that the power output of the PW1 would be increased to 5 kW continuous, 7kW peak.
    But, Ver 2.1 of the datasheet offered ‘Power,continuous & peak: 3.3kW.’
    Capacity changed from 7kWh to 6.4kWh, but called ‘Energy’.
    All other specs, including efficiency and capacity retention, remained measured at 2kW.

  23. Ronald – any further info regarding the inverter and the PowerWall-2? (I keep coming back here to see if any updates)

    • Ronald Brakels says

      Tesla has said they will send us the Powerwall 2 technical specifications, but they haven’t done that yet. Considering that it has changed on their website from a 13.5 kilowatt-hour battery to a 14 kilowatt-hour battery, they may not be sure what the technical specifications are themselves. But as they have said they will be available within 3 months I presume they’d have a pretty good idea of what its specifications will be.

      The information I have at the moment is the Powerwall 2 has a battery inverter that allows it to be AC coupled to any existing solar system. Whether or not there will be a version that can be DC coupled, I don’t know, but I suspect there will be.

      • Thanks for your quick reply. Figured Telsa keeping things to themselves (interesting as obviously there has probably been a few ($$$) orders already)
        I also interested in the control options having recently gone down, rightly or wrongly the enphase/microinverter full AC route.
        An AC Coupled Battery is one thing – but who/what hardware is going to offer the control of excess power into battery and out of battery at suitable times in the AC coupled world?
        (and options for utilizing battery in event of grid-loss?)

        • Ronald Brakels says

          Presumably the AC coupled Powerwall 2 installation will involve clipping sensors onto the power cable coming out of the solar inverter and the power cable coming into the house. This way it will know to charge when solar electricity is being exported to the grid and discharge when electricity is being imported from the grid. A simple timer will allow it to take advantage of time-of-use rates but maybe Tesla will provide something a little smarter than that.

          As for using the Powerwall 2 for backup power during a blackout, I don’t think that would be possible without additional expense as it would require being able to isolate the home from the grid and a simple AC coupled installation won’t allow that.

          Tesla says the Powerwall 2 supports off-grid and backup use, so presumably there will be some way to install it to make use of those features.

  24. Not much is being said about the SolaX storage system….here in NZ its seen as a very good solution, providing off grid backup, as well as a fully integrated on grid storage system, equal at least to anything on the current PV storage market…Not only is the hardware reliable…but SolaX China will replace without question any part of the system including shipping within the Warranty.. I suspect that SolaX Australia will do the same for Aussie buyers.

  25. What about using it for pure load shifting? im in NSW and the peak rate (2pm – 8pm) is 45¢ per kw/h. So theoretically you could use it with no solar installed and jus charge it off peak overnight for use between 2pm -8pm?

    • What is perhaps not obvious is the maximum kWh that storage can deliver. In the case of an Enphase 1.2 kW Storage Battery the maximum given up to consumption in every 15 minutes is 60 watt-hours or 240 kW per hour. A supplier in Victoria has introduced a seasonal demand charge where they sample in half hourly time slices the maximum kWH consumption between the hours of 3:00pm and 9:00pm. The formula is the [maximum 30 minute watt-hours in the sample range x 2 or 1.2 kWH minimum x Daily Rate x Days in Billing Period. The point is if you are subscribed to this type of plan you are never going to be able to beat the seasonal demand charge with storage because it is not based on actual consumption.

  26. Any chance you could run the numbers on new build housing considering going completely off grid?

    Connection charges especially where there is a hundred metres or more to the grid would make this viable pretty rapidly now I would imagine?

    • Erik Christiansen says

      Malcolm, the numbers for running fully off-grid would be pretty variable, I figure. A quarter of a century ago I had to pay a couple of thousand to extend the grid just two poles to my house here in town. But out on the farm, the several km would have cost over $60,000 over 30 years ago. And we’ve just been warned that after closure of the Hazelwood power station, Victorian power prices will increase. (More than they’d increase without.)

      But does that make the farm a no-brainer for a big PV & battery installation?
      With a gas fridge, gas cooking, and wood heating, we only run a modest generator from sunset for a few hours for lights, computers, & TV. It costs about $5 per night, especially after I put in LED lights, and we’re only there about a week a month now. The generator has lasted over 25 years, though we’ve swapped the Honda motor out. When the output gradually sagged to 190 Vrms, I measured what phase capacitor value it took to bring it back up to 240V, then bought a motor-run capacitor of suitable value off the internet for $7, and it’s as good as new.

      If I can just expedite my move out there, then the economics of generator vs PV & batteries changes, but going on-grid just isn’t viable out there.

      In town, the external variables probably diverge much less, but numbers of aircons, dishwashers, fridge/freezers, spas, swimming pools, occupants, rooms, passive solar efficiency, … can be all over the shop. If I had to have something to help quantify the cost/benefit, I’d start putting together a spreadsheet, with e.g. dishwashers and 70% of aircons drawing off PV, and lights consuming battery power. Input your bedtime in addition to all the other selections, and it’d spit out a guess at your required array size and battery capacity. But then that’s a service that installers provide, without you having to look up your insolation numbers.

  27. What is your worst kWh consumption per day in the period 01 Jan – 31 Dec?

    For off grid the installation would involve PV + Storage Battery + Backup Generator. If it is a new build you would have the house wired to support the backup generator.

  28. I think the worst is around 25kwh – but that isn’t exactly relevant.

    (a) I want to go quite a lot smaller (at least initially) for the new build

    (b) I won’t be using electricity for heating

    I am quite prepared to make some changes in terms of load shifting and energy usage generally and if at all possible I’d rather use no fossil fuel at all (so no backup generator and no gas)

    Looking to make a large solar hot water heat bank – to be used for hydronic heating and household hot water This may have a wood fired backup.

    I guess my question is how well the Powerwall 2 fits this scenario or is it likely the price competition will see better alternatives?

    • Ronald Brakels says

      It sounds like the Powerwall 2 won’t suit your situation, Malcolm, if you are looking for it to pay for itself, as it does not sound like you would be using it at high capacity. But things are changing rapidly. You may not have to wait too long for a smaller system to become available at a price point that will make it worthwhile. Once the Powerwall 2 actually starts being installed other battery makers may drop their prices. (Or maybe drop out of the market.)

      • Thanks for your reply (and one earlier from Finn? – somewhere in this thread I think!)

        I guess while value for money is of course important my number one priority is probably a turnkey solution that is either easily scalable as my needs grow (I’ve heard mixing battery ages is bad?) … or something with, initially at least more than enough capacity that I can grow into. If that gets me more than 10 years down the track – who knows what options will then be available – but a lot cheaper is a safe bet (I hope by then to have an electric car which could be integrated into the system)

        The other factor is I really like the idea of being off grid and would like also to be fossil fuel free so am prepared to pay perhaps something to do that and/or make compromises to achieve that goal.

        If you think Tesla is still not a good fit, does that mean that I should be looking at other battery technologies (all of which have just had some cost pressures applied) or other lithium offerings with smaller capacity increments.

        Sorry if this seems incoherent – I can build houses but while I have been looking at off grid for quite a while now, something about electrics turns my brain to mush!

        • Ronald Brakels says

          Malcolm, when I answered your last comment I had forgotten that you had mentioned going off-grid and I assumed you were talking about using a Powerwall 2 on-grid. Sorry about that.

          Because of its low cost a Powerwall 2 is likely to be one of the most economical ways to go off-grid. However, it is still very unlikely that people who are currently on-grid will be able to save money by going off-grid with one. I’d say it is just about impossible. I will run the numbers on this and get something written up before too long.

          • Erik Christiansen says


            Malcolm also initially mentioned that it’s a “new build”. If that involves running power to the block, several tens of thousands of dollars could potentially be offset against off-grid infrastructure. Even a 200 m underground cable to powerlines costs quite a bit, and paying for extending the network past the property has bitten me personally.

            But if the new build is merely filling a vacant block with power already there, then I wouldn’t bet my socks on your figures coming out rosy, just yet. (But will read them with interest when they’re published. 🙂

          • Yes as Erik says my interest is in building again. The last house I built is nearly 10 years old now (but I haven’t aged at all!), 100 odd metres underground was around 5 grand from memory but I’d imagine that would be significantly more now and of course as I like my space the distance this time may well be greater.

            I’ll be interested when you get to it but as I really want to go off grid anyway I don’t need a lot of convincing;)

            It seems the PW2 still needs another inverter. Any suggestions as to suitable models and pricing?

          • Ronald Brakels says

            The AC version of the Powerwall 2 won’t need a separate inverter, but the DC version, which is what I assume you will need to go off grid will. There is no information available at the moment on what might be compatible.

  29. Sizing a system can be difficult because there are so many variables including where you are located [Lat/Lon] that have an effect on both production and consumption.

    We are located in Far North Queensland [FNQ]

    We have a 5.75 kW Enphase + 1 Enphase Battery 1.2 kW [1 x battery Installed Sept 16 to obtain performance data for system sizing]. On the consumption side [3 Bedroom House + 1 Bedroom Apartment] we support [Item, Units Hours of Operation] Pool Pump 1 : 8, Pool Heater 1 : 5 [Oct-Mar], Split Solar Hot Water 1 : 3 [Booster Only], Fridge Freezer 1 : 24, Bar Fridge 2 : 24, Air-conditioning 8 : [Oct-Mar] occasional, Induction Cook Tops 2 : 1, Oven 1 : 1, Microwaves 2 : 1, Dishwasher 2 : 2, Washing Machine 1 : 2, Dryer 1 : Occasional.

    We have the Pool Pump, Pool Heater, Split Solar Hot Water [Booster] and Apartment Air-conditioning Timer Switched.

    The cost to run the split solar hot water is the watt-hours used by the pump to circulate hot water in the tank over the roof panels. We have the booster set to when solar power is available. The net result is that the cost of our hot water is negligible. If I was to recommend a hot water system it would be evacuated tube on the roof and storage at ground level.

    The main Fridge [in the house] and all Lighting is wired for connectivity to a 2 kW Honda Generator Model [2.0i] backup for the Grid.

    This is our daily kWh performance for July 15 – June 16
    Grid Usage [14.41] Feed In [9.62] Storage [0.00 – Installed Sep 16] Produced [24.78] Consumed [29.57]

    This is the daily kWh performance Forecast for July 16 – June 17 Grid Usage [13.97] Feed In [8.43] Storage [1.06] Produced [29.59] Consumed [34.07].

    The 1.2 kW Enphase Storage Battery charges and discharges at the rate of 240 watt-hours. The actual household consumption at that time might exceed the capacity of the battery even though it has power available.

    If you post an email address more than happy to provide you with an image of the user interface of our systems data analysis.

    Our next project is to change all our lighting from 240v CFL to 240v LED [there will be a payback but I am yet to crunch the numbers]. If you leave an email address more than happy to provide you with a copy of our systems data analysis.

    I hope this was helpful my only advise is be prepared to have to resize your system and that option should be built into the original purchase.

    And finally for July 15 – Jun 16 without Solar our energy cost would have been $3,101.28 and with Solar PV only $1,520.62 a saving of 50.97%.

  30. Howard Patrick says

    What Ant says reveals the complexity of home storage systems especially when you consider the coming age of the EV.

    It seems that block-chain technology will open the way to very effective distributed energy storage.

    Rather than homes having their own battery to storage surplus energy energy could be directed to local MW storage facilities and drawn upon as required. Perhaps a small home battery and the EV battery topped up before the surplus energy generated being sent away.

    This link will indicate where my thought are coming from:-

    If we actually had an innovative Prime Minister or even one that did not have his hands tied behind his back by the likes of Abbott and fellow right wing religious conservatives, invariably climate deniers or doubters, we would already have whole suburbs being planned around such technology.

    Despite the LNP this type of development is beginning; like at a housing complex in White Gum Valley, near Fremantle, WA.

    • You don’t need battery storage when the simple solution if available was net metering.

      What contributors to these pages have not discussed in any great detail are the costs and return on investment that relate to domestic and/or commercial installations based on an analysis of issues like the financial status of the purchaser [employed, unemployed, pensioner, body corporate], funding, cash flow, loss of opportunity costs, taxation, depreciation, inflation, asset testing [Pensioners] warranty, useful life of the system, the cost to get in and cost to stay in just to name a few of the issues.

      Of course not all of the issues relate to any one installation so generalised comments as to what the real cost per kWh for either PV or battery storage simply may or may not apply. There have been some projections as to the cost per kWH for the Powerball 2 which appear not to take into consideration the real cost after taking into consideration what applied at the time of acquisition. As a case in point a commercial installation where depreciation and energy costs can be offset against taxable income. I cannot see a company like Bunnings investing in Solar which does not have a positive effect on the bottom line [profitability].

      If you want to know the real ROI and you know the system cost and likely production and consumption performance good idea to talk to an accountant with a comprehensive knowledge in matters of Cash Flow Personal and Company Tax, Government Subsidies, Energy Supplier Billing Strategies just to name a few.

  31. john nielsen says

    Hi Ronald,
    I enjoy reading and learning all from your research, and your bloggers comments.
    When will the Powerwall version 15 be available?
    I am totally off grid 24/7 except night time aircon. I would not think of quitting the grid even though I have a 36 kWh lead gel battery system running from a 6 kW micro inverter system.
    I believe the ideal system for many people is to have a PV system sized accordingly to their needs, i.e. export as little as possible, if any and stay on the grid.
    If you have a 3 kW system and you produce 15 kWh daily, then try to use all of this power during the daylight hours, and forget about storage for the next 5 years.

    If you have a large consumption, and need a 10 kW PV system, then you can also have that, but not connected to the grid. You can run such a system from just 4 car batteries and a couple of inverters (separate from your micro or string inverters if you have such), plus relay driver, some relays and other bits. You will not have any power at night from this system and accordingly when the sun sets and your battery voltage drops below a relay driver threshold, your system will automatically switch over to the grid.

    Remember, you can have as much PV as you like as long as you don’t connect it to the grid and why would you for 6 cents hWh. So a hybrid system, I believe is ideal, at least for some years to come.
    john nielsen, Silkwood

    • Hi John when promoting anything that does not necessarily meet with Australian design laws, government legislation or regulations, terms and conditions imposed by Energy Suppliers it might be a good idea to provide as party of your commentary a disclaimer to the effect that any fixtures or fittings added to the dwelling are not guaranteed fit for the purpose and that written approval from appropriate authorities including the insurer should be obtained to avoid building, contents and/or public liability insurance is in accordance with the policy terms and conditions. My understanding is that in matters of insurance it is quite a common business practice for the provider to look for a reason on which any submitted claim can be denied. Car insurance is a good example especially if you modify the vehicle from manufacturers specification without their approval. What you do is your business because it is your risk however to promote an idea or alternative other than a commercial solution may also result in you creating for yourself a contingent liability. PS I am not qualified to give advise and deny any liability on any account whatsoever should you or any other party choose to act on all or any part of it.

  32. john nielsen says

    Hi Ant,
    I hear you loud and clear. I don’t believe in having any installations not complying with the rules, being the SAA wiring rules or the Grid supplier’s rules, and also as you mention insurance.
    I am not promoting any PV system not complying with all of the above. I have in writing from my grid company Ergon, that I can have as much PV as I like as long as I don’t connect it to the grid, and of course, I wouldn’t dream of selling power for 6 cents kWh.
    I believe you are correct on the insurance, not just for fire, injury but also if you have a mortgage, I believe all boxes should be ticked. Of course my suggestion refer to the design being carried out by an electronics engineer as well as the high voltage hook-up be carried out be an electrical contractor. I have no understanding of insurance, except I believe it be of utmost importance for most people. We have had 3 cyclones here in the past 26 years, and I have seen the 22 kV power poles laying out in the streets all broken. If I am promoting anything Ant, it is for people to forget all those fancy battery systems and stay on the grid while having a minimal PV system exporting a minimum to the grid, and complying with all the rules. I don’t give advice on insurance, I have none.
    PV is here to stay, and I can understand people being anxious to quit the greedy grid, but I cannot see the purpose for some years to come and if I remember correctly, this has also been the opinion of both Ronald and Finn.
    john nielsen, Silkwood.

  33. john nielsen says

    Hi Malcolm,
    About inverters: I use MPP Solar inverter, 5 kVA, 4000 Watt, pure sine wave, MPPT 80 Amp charger, ,,less than $1,000 on Ebay. You can couple two or more together if need be.
    There are a couple of good ‘youtube’ on PV, one is a guy in WA ‘Justin Case’ who has a similar set up to mine, and another is a guy in the USA, name ‘Mark Kash’. Grid tie inverter without a grid ‘ the latter has a couple of dangerous issues, but principally a good setup.
    Again, this is only for people intending to quit or minimize the grid use, as well as having the qualifications to do it, meaning, being able to draw up a wiring diagram of your proposed installation, purchase all the gear, and then seek a licenses contractor to wire it up for you..
    I cannot see the cost benefit of those new types of batteries thus I will stick with my 157 year old technology ‘lead acid’ , but will anxiously continue reading about PW number 9.
    john nielsen, Silkwood.

  34. Interesting article.

    Could you also include cost of rising electricity prices? Say based on the cost per kw increases of the last 10 and or 15 years and project that forward.

    The ongoing increasing cost of grid electricity would make the power wall very cheap in my view, but i don’t have the accounting skills to do the math.

    Asumming you could puchase the thing for cash upfront.

    • Ronald Brakels says

      Hi Jason. In the article I simply assumed electricity prices would rise in line with inflation. If electricity prices rise faster than inflation then a Powerwall 2 could certainly pay for itself, but I would say if an economic return is wanted then people should wait until the cost of electricity is high enough to make batteries pay and not before. So if you think electricity prices are going to rise the best thing to do is wait for the combination of rising electricity prices and falling battery prices result in them paying for themselves.

      If someone wants a Powerwall 2 mostly for non-economic reasons but hope rising electricity prices will result in it paying for itself, then they are taking a gamble.

  35. Well, if one believes in yet another ‘Yes Minister’ review released just yesterday apparently, then everyone can be assured that electrickery prices will rise. Here’s just one article covering the story:

    Personally, I can’t fathom the logic of any rise because previous rises were supposedly caused by the costs incurred by infrastructure improvements in the poles and wires. Whilst I accept that EVs will add some dimension to the equation, the advent of battery tech will surely offset the perceived and forecasted strain on the current system. But then, what would I/We know.



  36. If you live in QLD and have not already done so this video is designed to soften up the consumer to accept the rationale behind the need to change residential tariffs sometime after March 2017. It is a must watch.

    What is likely to be introduced in addition to Usage, Meter and Supply Charges are Seasonal Demand Charges. Seasonal Demand Charges are based on the maximum kWh you consume in a prescribed time period likely to be 3:00pm to 9:00pm. A different daily rate is likely to apply for the period Dec 1 to Mar 31 and for the period Apr 1 to Nov 30. The formula is [Max kWh used during the sampling period or n.n kW which ever is the greater amount x daily rate x nn billing days].

    With these changes if they occur there are likely to be winners and losers. Who are likely to experience the best outcome my guess is those with PV with storage capacity for excess production. For best results you would have to have enough storage to cover consumption during the out of sunlight hours [6:00pm – 9:00pm]. The result would be to reduce the seasonal demand charge to the minimum based on kWh. Obviously this is not an issue for those who are already off grid.

    • Ronald Brakels says

      Pet peeve: Unlike what the video says, electrical energy is not transmitted at the speed of light. Two-thirds maybe. If we could get energy to move at the speed of light through a cable I probably wouldn’t get my head blown off by plasma rifle fire so often. I could totally beat those foul mouthed American 8 year olds if I was propagating electromagnetic waves through a vacuum instead of wriggling electrons in a piece of copper and then bouncing photons atom from atom through a glass thread.

  37. Some futher information;
    Powerwall is supported by the following inverters: Australia SolarEdge
    For Solar Self-Consumption Only
    Powerwall 1: SE2200*, SE3000*, SE3500*, SE4000*, SE5000*, SE6000
    Powerwall 2 (DC): SE2200**, SE3000**, SE3500**, SE4000**, SE5000**, SE6000**
    * Must be installed with SEST1-S1 StorEdge Interface
    ** Must be installed with SEST1-S2 StorEdge Interface

    (The listed inverters are current SolarEdge products, I believe. As earlier, they need the StorEdge Interface to charge from solar. DC battery input is limited to 3.3KW for those models. )

    For Solar Self-Consumption & Backup
    Powerwall 1: SE5000-AUS1, SE6000-AUS1, SE5000-AUS2, SE6000-AUS2
    Powerwall 2 (DC): SE5000-AUS2, SE6000-AUS2

    (This category covers back-up, too. There is no current datasheet from SolarEdge for the AUS2 versions. I think, perhaps, the inverters with the ‘2’ suffix can charge the battery without the StorEdge Interface, and/or from the grid. Makes sense of the additional back-up option.

    The Installation manual is vague about battery power input. Promises double power capacity, though new hardware would be required.

    Then, Fronius
    For Solar Self-Consumption Only
    Powerwall 1: Fronius Symo Hybrid 3.0-3-S, Fronius Symo Hybrid 4.0-3-S, Fronius Symo Hybrid 5.0-3-S
    Powerwall 2 (DC): Fronius Symo Hybrid 3.0-3-S, Fronius Symo Hybrid 4.0-3-S, Fronius Symo Hybrid 5.0-3-S

    For Solar Self-Consumption Only
    Powerwall 1: Sunny Boy Storage 2.5 (SBS2.5-1VL-10)
    Powerwall 2 (DC): Sunny Boy Storage 2.5 (SBS2.5-1VL-10)

    (Despite the promised AC version, the same as the earlier AC coupling option. No warranty for the AC version yet, and perhaps no PW2 AC ?)

    • Ronald Brakels says

      Thank you very much for that.

    • I don’t know very much about batteries – what’s the difference between self consumption and backup?

      • For some Solar aka PV systems have a language all of their own. I hope this simple explanation is helpful. No sure what self consumption means perhaps in my explanation it is simply the same as consumption.

        Production refers to the amount of kWh the PV system produces in any period.

        Consumption refers to the amount of kWh that the household consumes in any period. Production can be more than consumption in which case the excess can be stored in a battery or feed to the grid. When production is less than consumption then the power short fall can come from storage or the grid.

        Backup is a power source when you have no production, storage or grid power available for current consumption. In this case Backup could be a Generator.

      • Ronald Brakels says

        Hi Sam. Here in South Australia we pay around 29 cents a kilowatt-hour for grid electricity but we only get around 8 cents for each kilowatt-hour of electricity from our rooftop solar systems we send into the grid. So if we self consume the solar electricity produced we save more money than if we sent it into the grid for the feed-in tariff.

        People can increase their self consumption of solar electricity by doing things such as setting dishwashers, pool pumps, and so on to work during the day, heating or cooling their homes before the sun sets, and putting their hot water systems on timers so they turn on during the day.

        • You cannot assume the total kWh production during daylight hours will be sufficient to run your household energy consuming resources. But it is probably good practice to timer switch pool pumps and solar hot water boosters to run when Solar production is most likely to be available. As for other devices like air conditioning, dishwashers, washing machines, cloths dryers then your option on overcast days is to check your current production before switching on the device. What might be helpful if you like automation you can probably control the availability of power to any of those devices with an application called Apple Home installed on a smart device that controls Home compatible hardware. Some claim that dismounting CFL [compact fluorescent globes] and replacing them with 240v LED have a reasonable payback based on the energy they conserve. They are still expensive [slowly reducing in price] so you might start with those lights that are on more often then not.

      • Oh one part of your question that I did not respond to and that is Batteries. To gain some experience with storage we purchased a 1.2kW Enphase storage battery that is connected to an Enphase 5.75 kW PV micro invertor installation. If you graph a perfect days solar production it produces a perfect bell. So on those days you only get to charge or top up the battery once on the assumption that production is more than consumption. That sort of lays bare that you cannot possibly get two cycles of the battery especially where solar production is at its best [requires a production event that can double the storage capacity during sunlight hours]. The best result we have every achieved is about 1.287 kWh during sunlight hours [during sunlight hours consumption drawn from storage during the day and topped up]. Ok so our battery has a charge and discharge rate of about 240 watt hours. So even if it was fully charged and the consumption at the time was say 750 watt hours then 510 watt hours is going to have to come from somewhere in our case the grid. Given that the system manages the production, consumption, storage and feed in flow of energy in real time sizing storage because of the many variables may not be easy to predict. Our micro inverter system allows us to upgrade our PV and Storage system in steps until we get a reasonable balance between production, storage, consumption and feed in. Our next step is to upgrade the PV from 5.75 to 7.99 kW [23 existing + 7 new totalling 30 panels] We have been keeping daily records since July 2015 which we would be more than happy to share on request.

  38. paul simpson says

    Hi..very interesting

    My main concern is with safety – not much mentioned !!!

    What happens when one of these blows up ?
    If I see my neighbour attempt to put one anywhere close to my house ill be up to council pront.
    Not only will it blow out her wall but will take my kitchen wall with it.
    Also fire risks???
    Will house insurance cover explosions?

    A 44 gallon drum cant be kept in the house or anywhere near it for obvious reasons.

    So what regulations are in force for locating these unnecessary monsters down in the shed?
    plus the associated cost.

    Make the feed in tariff = feed out tariff then theres no need for any battery (even if they were free )
    Its trying to make 2 wrongs make a right.

    • Ronald Brakels says

      Paul, you may want to check what’s in your pants. If you have a device in there that lets to talk to people at a distance, then you are happy carrying an explosive device next to something more valuable than your kitchen wall.

      • paul simpson says

        but thats my risk
        I wouldnt expect anyone else to carry my phone and take my risk!

        Also the bang from a solar battery would be 1000x more than the phone.

        -a somewhat different argument

      • Jack Wallace says

        hehehehe….the only device in my pants that talks to people at a distance is called ‘The Wife’………..Gets turned on a lot, and often goes off without causing any serious damage. 🙂

  39. If tesla can do 100mw for s.a for 100million how come you cannot buy a tesla power wall for about 1300-1500 dollars which is the same relative cost per kw. Where is the extra 7500 in the systems?.

  40. Hey. Can you explain how you reached the 40,680 kWh?

    • Ronald Brakels says

      That’s a good question, Beatriz. We now know the usable capacity of the Powerwall 2 is 13.2 kilowatt-hours, but at the time I wrote this article I should have only had Tesla’s 13.5 kilowatt-hour figure to go off. If it deteriorates to 70% of its original 13.5 kilowatt-hour after 10 years, and for simplicity I assume it does so linearly, then if it’s fully cycled each day the average cycle would be 11.475 kilowatt-hours. After 10 years that could total to around 41,900 kilowatt-hours, which is 3% more than what I put down and knocks the price per kilowatt-hour from 26 cents to 35 cents.

      Fortunately, my next calculation appears to be correct, so I guess I just made a calculating error and didn’t notice when I checked the figures because it looked close enough to be correct.

      The information in this article has been superseded by new revelations from Tesla, but I had better still go and correct it.

      That for alerting me to this, Beatriz.

  41. I don’t know how i got here, but i found it very useful and pertinent information…however, and besides my poor english, (and even poorer knowledge on the subject), i’ll try a question “off the topic”, but that intrigues me…: can a PW be a viable ‘powerbank’ on a EV?… (i live in a country with very high taxes on grid and even higher fuels,and never understood (or maybe did) why EV avoid battery swap solutions, wich could make a huge difference on this deal…).

    • Ronald Brakels says

      Hello Numo. Technically a Powerwall could be used as a low power electric vehicle battery, but it would be cheaper and easier buy lithium batteries that aren’t part of a home energy storage system and use them.

      Given that batteries are continuing to rapidly fall in price and that “superchargers” such as the ones used by Tesla cars can rapidly charge electric vehicles, I doubt we will see battery swapping. It is still possible a company may try it, but it seems unlikely to me.

  42. The information on this page is fabulous but I don’t even care …. I frequently found myself laughing (in a good way) as I was reading it all !!!

  43. If the battery is guaranteed for only ten years, as apposed to the usual 25 years, AND it takes ten years to pay for itself, what have you gained?

  44. peter duxbury says

    Pity that the Powerwall batteries are terribly expensive, as they could be adapted for driving moderate-size EV’s. It would be good to be able to carry a fully-charged Powerwall 1 in a Nissan Leaf – in case you get caught short somewhere, with a flat battery! Like we carry a Spare Tyre!
    Also, speaking about Power generation, just about every house has a Water Meter. The water is under pressure. I can foresee a day when the Water Meter drives a turbine, and something similar to a Ford 80W Alternator. Turn the taps on at full, and generate 12v x 80W = 960W of power – fed into the National Grid to offset your Electricity Bill. Currently, with the ‘drag’ from an Alternator, this may not work – or would be inefficient. But the possibilities are there for an Academic Challenge! In 2005, I installed a Hybrid System in my home, which is a 12VDC system. A 110Ah deep cycle battery is charged through the day, and all LED Lighting (inside and outside of the home) comes on automatically at dusk. All Lighting goes off at Dawn. Kitchen is brightly-lit throughout the night. This goes some distance in reducing the quarterly Power Bill. 110Ah Battery is fully managed by a $30 Controller. A cheaper way to lower your power bill than splashing out many thousands on a tesla Powerwall that may lose efficiency much faster that the time stated.My understanding is that the individual batteries in a Powerwall are all in series, and one hopes that any ‘failing’ batteries are automatically taken out of the Battery Circuit. Because “a Chain is no stronger than its’ weakest link”.

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