Will The Tesla PowerWall let you go off grid for $3500 ?

tesla powerwall

Will the Tesla Battery lead to a stampede of people leaving the grid? Photo: Tesla

[Update: Since I wrote this post (on the day the Powerwall was announced) Tesla have added some technical details that open up the possibility of installing the Powerwall for a much lower price than this blog post estimates. But – and it’s a big but – the cheaper installation will not allow you to go off grid. More details on the alternative install option here]


So Tesla has just announced a 10kWh home battery pack that costs US$3,500 (AUD$4,500) . The Tesla PowerWall will mount unobtrusively on the wall of your home and store your solar energy, so you can use it at night or when the grid goes down.

Lots of twitterers are proclaiming that Renewable Energy utopia has arrived. You’d be forgiven from thinking that, thanks to Tesla founder Elon Musk, all we have to do to divorce the grid is shell out three and a half grand.

Look – I don’t want to piss on anyone’s parade. This announcement is massive in lots of ways which I’ll get to soon. But you won’t be able to go off grid for that kind of money (yet).

Here’s what Aussie homeowners should know about the Telsa Powerwall

The really exciting stuff:


1) Battery Cost

The PowerWall was announced as a 10kWh Lithium Ion (Li-Ion) battery, packaged in a failsafe enclosure with a 10 year warranty. How does this compare with current battery costs? Let’s start talking Aussie dollars. At AUD$4,500 for 10kWh we are looking at $450 per kWh of storage. But… that’s for the “Backup Power” model which appears to be designed to only discharge the batteries on the rare occasion that the grid goes down.

What we are interested in is the US$3000 (AU$3800) ‘Daily Cycle’ model that claims 7kWh of storage which can be used every day. That works out at AU$550 per kWh of storage.

The best wholesale price of good quality batteries that I’ve seen in Australia is about $500 per kWh.

So why all the hoopla over what looks at face value like a 10% increase in cost?

Let’s go a bit deeper. Today, for $500 you get 1 kWh of storage with a Sealed Lead Acid Battery. This lead acid battery will last 1,200 cycles, or about 3 years, if it is used daily – according to its spec sheet. But to get 1,200 cycles out of it you can only discharge it by 60%. So the ‘useable kWh’ of the $500 lead acid battery is actually only 0.6 kWh.

The Tesla details are a bit sketchy, but if they are claiming 7kWh of storage with a daily discharge, then I’m assuming that is almost all usable (i.e. there is probably closer to 9kWh of batteries in the sexy white box and they never get discharged by more than 80% as per other Li-Ion batteries).

So to get 1 kWh of usable storage in a lead acid battery you are looking at spending  closer to $800. This makes the Tesla more like 2/3 the price per ‘usable kWh’ compared to good quality sealed lead acid batteries. Not bad. But wait, there’s more…

2) Battery Life 

The Tesla battery comes with a 10 year warranty and an optional 10 year extension. This is huge. Most lead acid batteries come with a 1 year warranty. Let’s assume the battery gods smile upon you and your lead-acid battery lasts as long as it’s specification (1,200 cycles). You have only got 3-4 years out of it until you need a new one.

If your Tesla battery is going to last 3 times longer, then its practical cost over 10 years is actually less than a quarter of a comparable lead acid battery. Now we’re talking!

3) Safety

If you buy individual lead acid batteries, you need to mount them in an enclosure. Then you need to wire all the terminals together. According to Australian Standards, this box should be outside. A compliant battery enclosure costs at least $650. Add the cost of putting the batteries in and wiring them up and you are looking at a total of $1,000 extra to house the batteries. With the Tesla PowerWall, the enclosure is included.

Also it is failsafe. Batteries sometimes explode. The Tesla batteries are surrounded by a chemical ‘gel’ that sucks the heat out of them if there is a fault and ‘thermal runaway’. This failsafe mechanism should allow you to put the PowerWall indoors without the worries you’d get with a conventional battery enclosure.

How does all this add up?


The Tesla PowerWall is offering Aussies 7kWh of usable, daily battery storage for $3,800.

Good quality sealed lead acid batteries in a proper enclosure would cost around $9,000 for the same amount of usable kWh. If they were discharged every night, they would need to be replaced at least once in a 10 year period, taking the total price closer to $17,000 (I’m assuming you reuse the cabinet).

There are other Li-Ion battery solutions out there for homeowners from the likes of Bosch and Sony, but last time I checked these were over $12,000 for 10kWh of usable storage in a safe enclosure.

So the Tesla announcement (if they can deliver on the promise) looks like it has reduced the cost of 10 years worth of quality batteries for your home by at least two-thirds.

That is awesome.

So can you now go off grid for AU$3,800 ?


Short answer – no.

While adding batteries to your home has just got a whole lot cheaper, it is not that cheap. Here’s why.

The PowerWall does not include a battery inverter.

The PowerWall contains batteries that use DC electricity. Your home uses AC electricity. You need an inverter to convert between the 2, just like you need an inverter for your solar panels. In fact the battery inverter needs to do a lot more than that, it also needs to integrate the batteries with your solar panels, your home circuits, and the grid. The sophistication of the control and regulation systems required to make this all work smoothly and safely cannot be underestimated; there can be a hell of a lot going at any point in time especially if you have multiple energy sources which can vary their output, and loads which obviously vary a lot too as we go about our daily life.

So you’ll need to add a Powerwall-compatible battery inverter that can do all this. The Tesla press pack says that they are working with a number of inverter manufacturers. I expect a compatible battery inverter to cost around AU$4,000 (disclaimer: that is a Wild Assed Guess).

Add in the cost of installation and GST, and you could be looking at around $10,000 total to buy and integrate the Tesla battery pack and battery inverter into your home solar system.

I fully expect Tesla to be working on their own inverter. In fact they’ll probably integrate it into the Powerwall for a fraction of the cost of a third party box.

But for now, I expect the inverter + installation + batteries to add up to around $10k in  Australia.

But what about going off grid?


Notice what I just said:  you should be able to add the batteries to your home for $10k. I did not say you could go off grid for $10K.

I think that staying connected to the grid (AKA Hybrid solar) is a much better solution – even with Tesla’s cheap batteries.

If you go off grid, you’ll need a lot more batteries, and you should also think about a source of backup power if you can’t top up from the grid. That starts to get expensive very quickly.

The disadvantage of keeping the grid connection is that you have to pay a daily grid connection fee. For most people that is about a dollar a day. A dollar a day that most people would rather not pay. Luckily there is a way you can stay connected to the grid and avoid these fees (AKA have your cake and eat it).

You see your connection to the grid can actually turn a profit for you – if your battery inverter is smart enough.  What am I going on about? I’m talking about another announcement today that you might have missed.

There is a little Aussie company in Canberra called Reposit Power. They have developed software that can be uploaded to a battery inverter. This software talks to the National Electricity Market, and does deals with them. To cut a long story short – it lets you trade your solar + battery power on that market instead of getting a piddly 6-8c from your Feed In Tariff.  Sometimes the cost on the wholesale market goes up to $13.50 per kWh (yes – you read that right!). If you can pump a few kW out in those peak times you are well on the way to offsetting your grid connection charges. This is not vaporware. I saw it up and running on a farm near Canberra a couple of weeks ago.

Reposit power announced today that the Tesla PowerWall will come with their software pre-installed on some compatible battery inverters. This may well mean that you can keep connected to the grid, with the benefits that brings of backup power and sharing of excess solar, while the software on your battery inverter turns a profit which will offset some – if not all – of your grid connection fees.

That’s big news indeed. Many people think the energy utopia is grid disconnection. It’s not. You wouldn’t disconnect your computer from the internet, and you shouldn’t disconnect your home from the grid.

The benefits of lots of  solar+battery systems all connected together – sharing power and flattening power spikes – are much greater than lots of off grid solar systems working in isolation. Now, with the smarts being developed by the likes of Reposit Power – coupled with the affordable battery systems that Tesla have announced – solar owners will be able to profit from staying on the grid. And that’s much better for the soul than railing against the injustice of 6c Feed In Tariffs and cutting the connection in a fit of anger. Grid connected solar with batteries has just become unstoppable. Bring it on.

About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of SolarQuotes.com.au. My last "real job" was working for the CSIRO in their renewable energy division.


  1. William Sharpe says:

    I love the timing on all this, as my olds have been talking about getting batteries once their 60c FIT contract runs out in a year or two.

    Theoretically, widespread battery storage and software like Reposit’s should bring down the average cost of grid-delivered power right? So long as companies like Reposit cannot use their software to create and then profit from price spikes.

  2. Mike Penning says:

    keep me informed please

  3. I think you need to fix up that inverter cost. $4k is a fair overestimate. Closer to $1k. The Tesla 10kWh battery has a PEAK POWER rating of 3kW. That means you only need an inverter that handles 3kW.

    • Absolutely not. You need a sophisticated inverter-charger that handles 3kW of output. That is a fundamentally different proposition to a simple grid connect solar inverter. It needs to handle bi-directional flow and provide UPS and islanding capabilities among other things. As the post says:

      “In fact the battery inverter needs to do a lot more than that, it also needs to integrate the batteries with your solar panels, your home circuits, and the grid. The sophistication of the control and regulation systems required to make this all work smoothly and safely cannot be underestimated”

      The current pricing for something that does this is between $4k and $7k per unit wholesale. So $4k is by no means an overestimate.

      I’m confident that this cost will come down as battery storage goes mainstream. But in 2015 this is the pricing you are looking at.

      • BarleySinger says:

        we’re looking at 10Kw monocrystaline with 10Kw battery and 2 SolaX inverters. That tends to cost $23,00-$24,000. Way out here power dos go down (and blinks). The grid is still good for foggy winter days, but the rest of the time…here in SA, selling your power (not storing it) looses you money.

        • Simple answer:- Buy a smaller system.
          And get a generator for the really cloudy days. (Try attaching a car/truck alternator to a concrete-mixer engine. That’ll crank out 90 amps for a cupful of petrol. (or free on woodgas.)

      • William Sharpe says:


        Does this change your assessment of the cost for a 7kw non-islanding system?

        • Hi William,

          Yes it is a fair point.

          If…. you are happy to have a battery without islanding, and you have a spare MPPT input on your inverter (or install a switch to switch the battery in to the inverter at night), and you are happy with a charger that operates on a simple timer (instead of interfacing to your inverter to ensure that you only top up with solar) then, yes, you may be able to add the battery to an existing solar install for $750 USD for the charger + $500ish for the install.


    • Bert Dunsford says:

      I recall Elon Musk answering this question about the DC storage in the power wall and I think someone said that we would have to spend some money buying an inverter. Musk I believe said “but if you already have a solar system installed would you not have a DC/AC inverter with your system?”

  4. Do inverters exist that could run solar panels and the battery? Im talking about a new system installed with solar and a powerwall at the same time. Or would i need to buy 2 inverters?

    • Hi Clay,

      The only inverter manufacturer that I know of that is working on an all-in-one battery and solar inverter that is being designed to work with the Powerwall is Solar Edge. I’ve no idea when it will be ready though!




    • Is there any real need for all the ‘automation’?

      I have a grid-connect system which is also connected to the (AGM ~ as good as any for the price) battery-bank via multi-input battery-charger which can handle AC/DC, including wind-gen and auto-gen).

      Any power I need is drawn directly from the batter-bank via separate circuits and run through several smaller (more energy-efficient) inverters and a DC cable. I also have several separate panels which keep the fridge/freezers and my computer running flat out all day (on a halfway-decent day) and maximise the power I’m feeding back to the grid.
      All the separate circuits are mix-and-match via four on/off switches mounted in the living-room.
      One doesn’t need to be an engineer to put it all together; bit by bit as the need or mood arises. Too easy.

      *The battery-charger is a Victron ‘Centaur’ ; 24/80-amp which does everything I’ve asked of it, but is not worth anywhere near the huge price. Poor material makes it susceptible to rust (and not just the casing, either), and the customer-service is non-existent.

      Lateral thinking should be the hallmark of any DIY-er/innovator.
      Automatic-everything makes you as much an industry slave as the ‘normal’ power-company does

  5. Athena says:

    Hi Finn
    Just got on board solar panels discussions in a serious way. Earlier this year I read on the BBC news website something about the University of NSW having created a cell that has 40% efficiency as opposed to the current 19.5% max efficiency. Have tried finding this article again but no luck. Do you know anything about this and if so, when can we be looking at such efficient solar panels being commercially available? I have limited appropriate roof area so solar panels that need half the current real estate would make a solar installation very much more appealing in my case now that battery storage and other efficiencies have also been upgraded thanks to Tesla.

    • Hi Athena,

      Solar cells will get to 40% efficiency at some point – but it is at least a decade away in my opinion.

      I know that some big manufacturers are looking to deliver 400W panels in the next 12-24 months which won’t be much bigger than the current 250W ones. Sunpower sell 327W panels right now.

      If you have limited roof space your options are either wait or put Sunpower 327W panels on any North, West, East or possibly even South facing roof areas too. At current pricing this can make sense.

      Also check with your local electricity network what max size they will allow – this may be a bigger constraint on your system size than your roof!

      Hope That Helps,


    • William Sharpe says:

      The UNSW announcement seemed just a little bit dodgy.

      It’s not a 40% efficient cell. It’s a bulky assembly of two standard 20% cells placed around a light splitter.

      The system does harvest 40% of incoming light, but you will not be putting one on your roof. Instead the concept may be useful for large-scale photovoltaic concentrator farms.


      I’ve heard of a 41-42% efficient cell in a German lab but that one is not “commercially viable”.

  6. Finn,
    Firstly the way you explain these thing, in a simple, informative, fun way is really appreciated. One question, how would the Powerwall interact with a Micro-inverter system. Do you think the two systems can work together, or are we looking at a battle between two different technologies,. Enphase with their new battery pods and the Powerwall. A bit like the Apple Vs. Microsoft of the solar world.

  7. Hi Finn,

    Obviously there is a lot of speculation about the exact configuration of the new Powerwall. My gleaning is that the Powerwall could have a MPPT that will charge the batteries within. The output from the Powerwall could potentially fed into a one string on a Grid Connected inverter such as a the SMA -21 series or the up and coming Fronius Primo where with consumption monitoring the Inverter is ramped and down according to the home load. If the output from the Powerwall is 350 to 400V DC then it would suit the DC input to one of the strings on these inverters. Therefore with Zero export controls supporting the inverters you might be able to draw down from the Powerwall battery pack during peak tariff rate times making this product potentially cost effective. Your thoughts.

    • Hi Simon,

      Yes – that could work – but you might as well use a proper battery inverter with all the safety, diversion logic and islanding controls in one, rather than wire together lots of discrete systems. Apparently SMA are soon to release a Sunny Island style battery inverter that does everything for around $2500. Can’t wait to see that.



  8. Philip Bramley says:

    Hi Finn,

    The Tesla announcement comes as an exciting development for battery storage – especially those who are “off-grid” with no intention of being “on-grid”!

    With economies of scale planned for his Tesla battery plant in the USA….with more to come…it will truly be a game changer for renewable energy and add another nail in the coffin of fossil fuelled energy.

    Ultimately, it should be in everybody’s interest to become “off-grid”

    • Hi Philip,

      Thanks for the comment. I actually think it is in most people’s interest to stay on grid. It means they can share their excess solar instead of wasting it, and with the emerging wholesale trading software that is already starting to be integrated into battery inverters, this excess solar will actually turn a healthy profit. Rather than getting 8c per kWh you will be able to get a share of $13.50 in peak periods.


      • As a do-it-yourselfer for probably longer than you’ve been alive, Young Finn, I entirely DISagree with your advocacy of staying on the grid.
        Buying and applying all the latest in hi-tech (or temporarily hi-tech) gear simply means putting yourself at the mercy of a slightly different kind of electrical industry/bureaucracy/political-machine. It entirely ignores (what used to be the point of) self-sufficiency, self-determination, and personal independence.

        Moreover, the way to avoid the endless agonising about what to do with the production of ‘excess’ power is to properly size (and operate) your system in the first place.
        There’s no reason anybody with half a brain (and perhaps a bit of self-discipline) can’t produce plus/minus 5% of their own power requirements. A good few people I know ~ including myself ~ have been doing just that for 30 years or more.

        Fiddling with the latest gadgetry may be great fun ~ if you can afford to indulge your whims ~ but is quite unnecessary. For a very long time it was only the people who DIDN’T have a shitload of money to spare who turned to DIY ~(solar) It disturbs me that the new New-Age baby yuppies are throwing around multi-thousand-dollar figures as though they were talking about peanuts. Quite a lot of people don’t earn/spend more than 10 grand a year all-up.

        ps. I can’t find my way back to a similar comment I posted yesterday ~ assuming it was published.

  9. I saw the Tesla release the other day and thought I’d check in with your Blog Finn – I still read all your articles even though I haven’t taken the Solar Plunge as yet – I like your honest advice!

    So when i saw the Telsa batteries I came here to see your take on them. Great article!

    But a coupla questions if I may:

    1) For home users up to 4 of the Tesla Batteries can be chained together – how does this affect your maths in terms of value and thoughts of going ‘offgrid’?

    2) What does an average household actually use per day, or just per night? How many of these batteries would the average modern house need??

    3) I noticed there was no mention of manufacture of these in Australia – So I’m guessing by the time the usual middlemen get ahold of them the price will be at least double to get one shipped to your door? Never mind the install costs … and what about warranty? I know its early days yet but is there any inkling of an Aussie supply chain/service?

    4) Telsa are publicly leading the way – but what/who else is out there offering somethign like this?

    Cheers for the good work Finn! I’m still reading when you publish new articles!

    • Hi David,

      1) Yep – you can chain them all together, and you will get economies of scale. Expect to pay at least 8K for an inverter-charger big enough to handle all 4, plus don’t forget to include a backup generator. The resulting price will be much cheaper than existing off grid systems – which is great. But I’m still a fan of staying connected to the grid if it is already at your house.

      2) The average consumption varies by location and number of inhabitants. A typical 5 person house uses about 22kWh per day. About 16kWh of that could be when the sun isn’t shining if both adults are working and the kids are at school 5 days a week. So the average house is looking at 2 Powerwalls to get to zero imports from the grid.

      3) The margins on this kind of stuff are actually generally really low – so I doubt they will be double the price. I’m not going to speculate what the cost to consumers might be because I haven’t got a clue other than that.

      4) LG are bringing out a 6.4kWh battery pack that is nicely packaged and will be competitively priced. Expect to see it on sale in Australia in the next few months. I’ve heard Samsung are in the game too.


  10. Leigh Phillips says:

    Hi Finn
    The way that I am reading the press releases from Tesla is that their battery system is designed to be plugged into one of the MPPT trackers on an existing Grid connect inverter. Very simple except that this opens a real can of worms, what happens when the inverter cries enough in its warranty period, who is liable? Particularly if the the power wall has been installed by other than the original system installer/supplier.
    Then there is the small problem of compliance with AS4777, will the installer of an additional powerwall be required to be CEC off grid accredited as is presently required with any battery hybrid systems, technically any electrician can install battery hybrid system upgrade to an existing system, but is this the way that these things should be installed? There are many unanswered questions in the press release that really need to be detailed before putting down your hard earned.

    • Hi Leigh,

      I totally agree. Tesla really should have had some technical bulletins available when they launched.

      And no-one non-technical realises that if you simply wire the Powerwall into an input on your existing inverter, you will lose all power if the grid goes down. I think it is fair to assume that if you buy a battery, you should have power when the grid goes down!

      The Tesla price point is brilliant, and I applaud their vision – but until the new breed of inverter chargers comes out with integrated islanding controls it is a bit naughty of them to imply that you can go off grid for the price of a battery + integrated DC-DC converter!


      • Hi Finn
        Have been talking with a builder mate who said if your trying hang 100 kg off a house wall you better get a structural eng to ok it.
        Next problem is us poor installers who have figure out some way of lifting this weight up onto its wall bracket, expect the share value of crane companies to go through the roof

  11. when you look on the tesla powerwall homepage you will find the information, that works with e.g. fronius symo hybrid converter, which handles both – pv-panels and batteries. it sells in europe for about eur 2.000,- with 3kW AC or eur 2.400,- with 5 kW AC.

    not bad, isn’t it`?

  12. Stephen Perrin says:

    Hi Finn
    I have been waiting for about five years now to jump into solar. I wanted to see the shakeup in the suppliers (Cowboys) & the price to get to mature stage & service cobwebs to be reduced. I live in SE QLD & have read hundreds of reviews from 2010 to now & notice that there is a complete lack of information to support the actual savings compared to what was advised in the purchase environment. I have no technical ability at all in regards to solar so I am grateful to have found your site. I have settled on a couple of Tier 1 (6 kw) panels manufactures to choose from plus a 5 kW inverter from SMA for $7,000 not a bad ROI. Yet to choose a supplier from the 3 who contacted me. The Telsa battery sounds impressive but I am leaning to again wait.
    What are your thoughts on current my purchase & position on battery??

    • Hi Stephen,

      Tier 1 panels and an SMA inverter is a good way to go.

      If will be fairly simple to add storage to that system using either AC coupling, or DC coupling using an SMA controller/inverter with the storage. SMA should be revealing a box that does this (minus the batteries) for about $2500 very soon.

      Payback without storage will totally depend on when you use your home energy. I’ve got a 6kW system which gives me a $33 power bill:



      • Stephen Perrin says:


        This is the system I am leaning towards based on our average KW/day over last 3 years of 40

        Jinko JKM265M-60 24 panels
        SMA Sunny Boy 5000TL 1off

        Would appreciate your opinion

        • Hi Stephen,

          265W x 24 = 6,360W = 6.36kW

          Jinko are good Tier 1 panels. The SMA is a great inverter. That will be a good system if it is well installed.

          Hope That Helps,


  13. VoodooCR says:

    If you discharge a Li-ion Battery 80% as stated in the article you will never get the cycles to match 10 years , you will all be queuing for your replacement TESLA 7kWh after 2 years !!


    A more realistic figure would be comparing a 60% DOD to give you the same Cycle life as your SLA. say 1200.

    TESLA 7kWh @ 60%DOD is 4.2kWh of Usable $3900AUS
    SLA 7KWh @ 60% DOD is 4.2kWh of Usable $3500AUS (since you need 7 @ $500)

    I dont think there is much between the 2 technololgies at the moment…..

  14. I am currently trying to decide between the Fronius Symo hybrid system, or going with Enphase micros, paired with Qcells Q.Peak panels. There is not much information about compatibility of micro-inverters with the Tesla powerwall, though Enphase apparently have their own AC battery system in development:

    The optimal system size for me now is around 4-5kW but to run my household in a hybrid system with minimal dependence on the grid I will need about 7-8kW in the future to power batteries, so expandability is a must – whether I go Enphase or Fronius.

    Does anyone have an opinion on micro vs string inverter setup for a system to be installed now, with a view to expansion and a battery system in the next 5 years?

    • Hmmmm – if you go Enphase – adding AC BAtteries should be very straightforward, and if you go Fronius Symo Hybrid, adding a Tesla Pack should be easy peasy as it claims to be directly compatible with Tesla’s Battery Management System.

      The most cost effective way is probably the Fronius – as Enphase micros do increase system cost by about 30% – and their batteries are probably going to be quite expensive too.

      But then you do get all the advantages of micros ( http://www.solarquotes.com.au/inverters/micro/ ) and aroung 8% more power with Enphase. Plus you can add a kWh at a time with their batteries.

      • It’s a hard one really. Right now the Symo Hybrid inverter is not available – a couple more months I’m told. And the price of an identically sized system with enphase micros for 4.2kW of Q.Peaks has been quoted at slightly cheaper than 4.2kW of Q.Peaks withe the Symo Hybrid. I have 3-phase and I gather I will need to get another string inverter if I go over 5kW anyway, so that offsets the increased cost per panel of micros if I bring my panels up to 8kW. Dilemma.

  15. What’ve you been smoking, Finn??
    Given the herd of provisos, complicated technology, other restrictions and ifs ands and buts all you’re advocating is swapping one industry-dictatorship for another ~ which will probably prove even more expensive.

    Given a battery-bank you’re not permitted to use unless it’s grid-connected (by a pricey electrician ~ probably ‘Industry Approved’ at an added cost) is like buying a new car without a fuel-tank.
    (If I pay for something it’s mine to use as I wish.)

    Pay a big price for a grid-connected battery and watch the GRID prices go through the roof ~ and you’ll be at their mercy. It defeats the whole principle of alternative/independent power production.

    My latest power bill, though being $200-odd in credit has, I notice Increased the price of peak-hour power by 18.5% in three months (or 75% pa.) ; off-peak rates by 5.8% in three months (23.18% pa.) and the ‘Service to property charge’ by 14.8% in three months (59%pa.).
    Imagine how I’d feel if I’d just spent $thousands on a system I wasn’t able to use unless I remained connected ~ and even then got bugger-all use out of because of the ‘stand-by’ function of the new batteries you explain above.

    With a modicum of planning and readjustment of priorities and althernatives I can buy AGM-style batteries that will suit my usage for the CURRENT price of ‘Service-to-property’ for about about 4 years. (And in my long experience a decent set of batteries, properly handled , can easily last twice that long.
    No matter how ‘cheap’ the new gee-whiz systems are they’re STILL a bloody sight more expensive than ‘free’. (Remember the years-long discussion about the free power solar-panels provide after they’ve paid for themselves? )

    And, usage aside, you can bugger up a very expensive battery, dedicated inverter, etc. etc. as easily as you can an el-cheapo Chinese one.

    Sort of like buying a RRoller you’re only allowed to drive to church…..and then getting run over by a truck on Sunday.
    Fair dinkum~!

    • Jason

      There are 2 key parameters that affect battery life. 1. Temperature and 2. Depth of Discharge. (DOD). For lead acid batteries to last 8 years we need about 3000 cycles. To achieve this we need to keep DOD to less than 25%. Ideal temp is b/w 20 & 25 deg. High temps kill a battery,which is why car batteries die at 3 years. Nothing to do with DOD. Not sure how you are handling this side of the issue. Hopefully you live in Tasie rather than Cairns.

      Now with a 25% DOD and assuming we need 16kwHr after sun goes down this gives a battery size of 64KwHr. At current AGM prices this is about a $35,000 investment. As grid connect fees are usually between $1 and $1.50 a day I am failing to grasp the maths of your argument. We seem to be out by a factor of nearly ten. ie – We spend $35,000 to save maybe $4500.

      Can you give some more info on your calcs and more than pleased to see any comments you have on my calcs. Always happy to be educated and learn.

      • Great post Peter. And 64kWH doesn’t include an electric vehicle charging at home either – guess we won’t be doing that anytime soon. Off-grid anyway…

  16. Hello Finn, The first time here, so here goes. People fail to realise that over 60% of their power bill, goes on lighting. If people really want to save money to go hand in hand with their solar power, why do they not just replace all of their 240 volt lighting throughout their homes with a 12volt power system. we did that 6 months ago, and our electricity refund has gone from from $65.00 to $330.00 for a quarter(3 months). Saving of approximately $265.00 per quarter, and would take 1.5 years to pay off. We have a 4.2 Kwh solar system. Total costing to change all of our 240 volt lights across to 12 volts, was a total of $1600.00, cost includes replacement of all lights and fitting by an electrician, including flood lights outside and all our 6 computers and 2 televisions, as these, all run on 12 volts as apposed to 240 volt we ‘save’. At night we use grid power for fridge/freezer, oven, spa.

  17. Robert Black says:

    Hi all. Just curious about a few things. I am currently about to build my own house and this solar B.S makes not sense to me. It seems every one has there own opinion and you dont know who to believe. A quick couple of things you should know before answering my questions. I have 3 Phase power to my house. Cost is not an issue I have no budget. I DO NOT WANT TO PAY FOR ELECTRICITY!!! Even if the figures dont way up. You have to understand I hate bills. In essence I am building a house that powers itself but is connected to the grid if something breaks or goes wrong. I also want the 7kw’s because the 10kw’s have less cycles

    1. Can the 7kw Tesla’s be in a sense, daisy chained?
    2. If so I am considering getting 3 to 4 of them as the 7kw capacity is not enough. I need closer to 20-30 WE USE A SHIT LOAD OF POWER!!!! However The biggest tesla rated hybrid inverter I can find is the Fronius Symo Hybrid 5.0-3-S. which has a 5kw max output. Does this mean I would need 5 inverters at 5kw output 25kw total for 3 tesla 7kw’s at (21kw)? Or do I only need 1 inverter and the daisy chained batteries are just storage and the excess power I generate once the batteries are fully charged is pumped back through the grid off the 1 5kw inverter? ( please try and keep the answer simple I am not a tech guru )
    3. Can the power walls tie into the Tesla car charger with out having its own panels?

    Any help would be much appreciated.

  18. Hi Finn,

    So if we looked at a solar panel system, with the Powerwall and the Reposit Power software, do you know of any companies offering this setup at present. We want to go this way with the ability to expand additional powerwalls when the price comes down…

    We are based in Sydney if that helps. Also having access to those interest free deals would be cool 🙂

    Cheers – Dallas

    • The installers doing Powerwalls at the moment that serve Sydney include Natural Solar, Solahart and Bradford Solar.

      I don’t know of any Sydney electricity retailers who offer Reposit yet – and that’s what is needed to use Reposit. As soon as a Sydney retailer offers a ‘Reposit Tariff’ it should be about $500 to install a Reposit interface on to the Powerwall.

  19. Jon Isaac says:

    Hi Finn, your estimate was off by a lot. 4,500AUD was too good to be true but almost made sense in ROI. 14,500AUD is about 24 years to break even. Any thoughts? Misled.

    • $4 500 turning into $14 500 is a joke … someone is making a HUGE killing there … and I doubt its the installer!

  20. I have 80kwh of Lead acid AGM batteries.

    They do not cost anywhere near some of the numbers quoted here.

    I got mine for $12600 including GST.

    I cannot come anywhere near that with Tesla powerwall.

    I run 3 SMA 5kw inverters mated to a Sunny Island 8.0 unit.

    Yes I am on an island off Tasmania and we never go above 20% discharge.
    We expect to get 20 years or MORE at that rate.

    We run two fridges, normal resistive hot water (the vaccuum tube stuff is a rip off, just buy more PV panels is what we did)

    We have NBN, foxtel, Xbox and we run a TIG aluminium welder.

    Forget the Powerwall….waste of money when AGM is so cheap now.


  1. […] I have pointed out in a previous blog post, the Powerwall is undoubtedly a major breakthrough in the world of solar battery storage. However, […]

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