Does your hybrid solar system really need backup?

Did you know that adding batteries to your solar does not automatically mean it is blackout proof?

The holy grail of affordable on-grid energy storage has finally arrived! Well, it’s almost arrived. Actually, it might be a couple of years before it really arrives and most Australians can get their hands on low cost energy storage systems such as the Tesla Powerwall, but they are coming and they will eventually be here. Adding batteries to your home solar (AKA a hybrid solar system) means that you will no longer be forced to sell electricity for 6-8c and buy it back, at night for 30c. Hurrah!

But when the holy grail does arrive you will have a choice, so take care that you do not choose poorly.

While a bad choice is unlikely to cause you to crumble into dust like the Nazi villain at the end of the second worst Indiana Jones movie*, if you what you decide is wrong for your particular circumstances you may live to regret it. Actually, I can almost guarantee that you will live to regret it, as it is really not a life and death decision. Unless you go about it in an astoundingly bad way, such as cutting power cables with an axe and then licking them to see if they are live, I can pretty much guarantee you will still be around to either rue or feel chuffed about your choice.

The decision to which I am referring is this: when you get your home energy storage system, are you going to choose to save money by using a common-or-garden anti-islanding inverter that only works when the grid is working (so won’t give you a single erg of energy to use during a blackout even if your batteries are charged)? Or are you going to pay extra for a specialist islanding inverter? These more expensive inverters will give you the ability to draw upon your battery power when the grid is down and laugh at the sound of your neighbours swearing as they bang their shins in the dark.



If you are lucky enough to own a grid-connected rooftop solar system, then there is an excellent chance you’re already aware that if the grid goes down you can’t get electricity from your solar panels . If you are not aware of this, then I’m sorry to have to break the bad news to you. Them solar panels, they ain’t gonna work in a blackout.

electrified worker

The crispy meat resistor dance.

The reason we are usually given for why solar inverters need to prevent islands forming is safety.

A line worker could come along and touch a cable they think is dead and go, “GHHHARRRRRRHHHHHHH!!!” as they do the crispy meat resistor dance.

And this is not a good thing. It never results in super powers. Some electrical accidents have resulted in people becoming bionic, but it’s not worth it. It appears that Steve Austin lied to us.

So anti-islanding inverters can potentially save lives.  And there are other reasons why it is useful, so anti-islanding is going to stay compulsory. No exceptions, not even if you bake the grid operators a chocolate koala.

Islanding Inverters


If you want to be able to use electricity from your batteries and/or solar panels during a grid outage, you are going to need an islanding inverter, which is a completely different kettle of fish. Or preferably electronic components. If it’s full of fish you should probably ask for your money back.

An islanding inverter, or off-grid inverter, will isolate the house and send no electricity into the grid during a power failure. It will let the house run off battery storage and/or solar panels. A generator can also be made part of the system. When done right, it can allow a household to completely ignore a power failure. Unfortunately getting a house ‘blackout proof’ like this costs a lot of money. Even a system that is just made to run lights, laptops, and refrigeration will cost a lot more than a simple anti-islanding inverter set up.

And if you are not keen on installing a dirty diesel a generator but still want self sufficiency when the grid goes down then things really start to get expensive. To completely ignore power failures an energy storage system will always need to have enough energy to get through the night. There must be enough solar on the roof to charge the batteries during the day even if it is overcast, and the batteries need to put out enough power to run household appliances normally. This can quickly add up to tens of thousands of dollars,  a huge amount of money to pay just to waltz through power failures. Sure, it becomes a lot cheaper if you include a generator, but if you have a generator why do you need an islanding inverter? Having to plug your appliances into a generator when the grid is down is less convenient, but foregoing a vacation to afford an islanding inverter isn’t exactly convenient either.

The Middle Way


There is a third choice for inverters that lies between anti-islanding and islanding. I presume this would make it an archipelagoing inverter. This is one that, when enough solar electricity is being produced, lets you plug appliances into a power point on the inverter and use it like a silent, non-polluting generator. However, the model I saw with this feature cost so much it was up in the islanding inverter price range. But they may not always carry such a hefty premium and so are an option that could be considered. They will of course utterly fail to produce electricity at night unless your neighbour has excessively bright outside lights.

Dollars And Cents. Or Probably Just Dollars.


The USB investment bank thinks $1,025 is sufficient to pay for an anti-islanding inverter that is compatible with the 7 kilowatt-hour Tesla Powerwall (or perhaps you can use your existing solar inverter for free ). And an Australian expert says that, as a wild ass guess, a suitable islanding inverter might cost $4,000. While I have no idea what feral donkeys have to do with his estimate, that sounds about right to me. Of course, it is possible to go cheaper than this. For example, last night in one of the dark, clammy, recesses of the internet; I discovered I could mail order an off-grid inverter for under $1,000. I assume it was made in international waters, as no country of manufacture was given. The company name looked like the output of a random password generator. And its warranty was for a single year. Sometimes choosing the cheapest product makes economic sense. This is not one of those times. I recommend it about as highly as I do licking a male platypus’s venom spur.

I am confident that islanding inverters will come down in price. This includes ones that are compatible with the Powerwall, as Tesla’s strategy is not to make money by charging licensing fees, but to make its patents available for free and allow competition bring down inverter costs and so enable Tesla to sell more energy storage. By the time Powerwalls or similar products are available in Australia, without significant delay I hope that suitable islanding inverters will be available for $2,500 or less. But hope is not a game plan. It is instead an emotional state characterised by optimism about either current or future events.

My Recommendation


Grid electricity works in Australia 99.9% of the time. That’s an average of about one day of power failure every three years. So I suggest that, unless islanding inverters really come down in price, the average Australian installing on-grid energy storage will better off with a lower cost anti-islanding inverter than paying extra for an islanding inverter and the ability to use energy storage independently of what’s going on with the grid. It may seem weird, or even just plain stupid, that during a blackout energy you can’t use storage sitting in your own home, and some old-school off-grid solar installers seem to think it is heresy. But it does save money and it should make better financial sense for most people to simply buy a small generator.

And if you don’t own a generator, that’s a good indicator that you don’t find power failures annoying enough to make the cost of an islanding inverter worthwhile. I would say that it is like Catch-22 because if an islanding inverter is worth it you’ll already have a generator and so won’t need an islanding inverter.


* If you do crumble into dust, I accept no responsibility.

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. Blackandwhite says

    spelling correction: UBS Wealth management no USB

    I disagree. Creating more pollution by throwing out a perfectly working inverter in a couple of years is crazy.

    • Ronald Brak says

      What? You’re saying I can’t borrow money from my computer plug?

    • Once again:- Could some clever engineer/computer-whiz (or any 5 yo!) find some way of the ‘anti-islanding’ gizmo on a basic grid-connect system so that they can be used in a stand-alone role???
      That way one not only doesn’t need to throw out a perfectly good unit (and save the horrendous price of a ‘purpose-built’ stand-alone inverter) but would get a unit that ~ according to the published figures ~ is a whole ball-park better in terms of efficiency and functionality.(Y’don’t need an automatic switch between 240v inverter/to battery-charger. Y’just leave your battery-bank permanently plugged into the household supply via a quality battery-charger.
      There are endless variations on such a theme.

      Meanwhile……anti-anti-islanding coversions???
      I for one can see such a big demand for such a thing I’d be prepared to put a substantial amount of cash on the line.

  2. ramjetski says

    Origin energy’s 6c/KwH is less than tempting. However in my last bill I have noticed that the tariff 11 charge as gone down to about 23.5c/KwH but that their ‘service charge’ as gone up 39.5% to about $1.16 per day! Talk about robbery and padding their shareholder’s profits! Origin can’t seriously make that case that their maintenance costs have gone up 39.5%!

    • Ronald Brak says

      Yep, they are really hiking up the “service charge”. And I have to say I really do feel serviced. They could have at least bought me flowers first. The service charge has nothing to do with maintenance costs. It’s all about profit maximisation. And the latest increase is about discouraging the installation of rooftop solar.

    • I recently posted (on here somewhere) the 3-monthly price-rises imposed by Origin and extrapolated them to per-annum percentages. They were ALL unjustifiable. (up to over 60% pa.)
      Particularly the ‘service-to-property’ charge.
      On challenging Origin (which by the way apparently has NO person or committee or process responsible for their price-settings ~ ask ’em!) I was told that the ‘service’ charge was set by SPAusnet, and that Origin was merely passing on what SPAusnet charged them.

      Challenged SPAusnet, and have been provided with documentation that Ausnet charges Origin $99 per customer PER YEAR to provide the service. (and Ausnet is among the more expensive distributors.)
      Origin charges ME just on $550 pa, (and rising in a non-subltle way!). As any 8yo kid could figure out that’s a 550% markup ~ and a 450% profit.
      ….and for NO added value.

      I will go off-line as soon as appropriate (ie when they stop sending me money on the FiT), and for others might suggest getting together and threatening Origin with a mass-migration of their business-base to other provider. (eg. Even unsavoury DoDo only charges 95 cents per day.)

      • ramjetski says

        Unfortunately I have just signed a contract with Origin for another twelve months. I like to get a paper bill. Other providers may pay a bit more for feed in tariff, but also want automatic payment deductions from my bank, and I won’t give anyone that ability, especially a power company. I have done some looking about and just about every other retailer has its fair share of critics, especially concerning customer service levels. Folks, we are all getting dudded and it all started with bullshit competition policy. Competition is the Trojan Horse of the commercial world. It promises everything and delivers nothing to the citizenry except higher costs and lower service standards. Yet we still swallow this line of nonsense at regular intervals in various industries. The only winners in my case are the shareholders of Origin Energy, because I am damned sure that their workers didn’t get a 39.5% pay rise. What a crock of crap.

  3. I agree with your recommendations to not worry about blackouts, unless:

    1) You think the network’s “death spiral” will result in poor service levels in the near future.

    2) You think a decline of fossil fuel energy is in the near future (the grid’s upkeep, as well as its fuel, is of course fossil fueled).

    3) You think network use fees will soon get so high that “cutting the cord” (not literally) will make good financial sense.

  4. Hi Ronald,
    I appreciate you writing this article but I think it would be much clearer to read and much easier for people to increase their knowledge if you left the ‘humour’ to the humourists. Your strength lies in your knowledge of electricity, and there appears to be much that you can teach people, but currently you’re diluting what is pretty good material with pretty bad ‘humour’ ( subjective of course).
    Look forward to reading the next article.

  5. Hi Guys, I have a 5KW Rooftop system installed by one of those companies that goes door to know the ones…anyway with 3 years of paying off the system (AGC I think) I thought what a great way to get solar and pay for it while saving on power cost..but ( game show Buzzer sound) No this is not to be.

    Somehow Origin actually charge me more since the 5KW System was installed.
    WTF? what was at the most in a very Hot summer of over 3 weeks of over 40 Deg C, an $800 MAX bill is before Solar, is now an $850 bill with 5KW system.
    Anyway I am fuming, I told them where to go and went to …block your eyes..Dodo, offering 7.2 cents and monthly up front payment of $117 per month. So far I have not received a bill in 5 mths.

    So a bit better, but my story does not stop there..sorry)

    I am in the process right now of adding Batteries, inverter and regulator to the existing system.

    3000w / 9000w LF inverter charger
    80amp Outback mx80 Reg
    440ah @24v AGM battery bank. (and cables)

    Total cost 3;3k approx for the above.
    plus maybe a few circuit breakers and sundry items.

    Right now I have the AGM bank setup with the 24v Inverter / charger going.
    I changer the batteries during the day and use the batteries at night.
    The house runs fine, remembering I am limited to 3000w at one time 🙂

    HWS is a Chromegen heat pump in eco mode,less than 500w, this was free from some Gov scheme.

    Soon I will buy the Outback Mx80 Regulator $980 delivered.
    and guess what…..yep AXE through the Grid power cable (JOKE)

    For me Stand alone makes better sense, for a little over 3k and approx 10 to 12 years out of the $1500 AGM battery bank I think I can beat the power Company.

    And NO bloody Bills..cheers guys 🙂 ..Steve

  6. It’s now March 2017 – with the new Tesla powerwall thingy and dire predictions of future power outages due to naff decisions by the various government peeps, is an islander system now more viable so I can have power while there is an outage?

    • Ronald Brakels says

      Costs have come down, but still not low enough for an islanding inverter (or multimode inverter as they technically should be called now) to beat a small generator for households, unless perhaps the situation is exceptional. We will have to wait until the new Powerwall 2 starts being installed before we will know for sure what sort of back up capability it has and that won’t happen until next month, according to Tesla. They have said it will have backup capability, but haven’t given any details. So fingers crossed its backup capacity will earn it fame and not be lame. However, I am not hopeful.

      • I didn’t realise the new powerwall wasn’t available yet. I don’t want a generator as I don’t know how to start one and am not interested in learning. What I would like is a system that sees me storing excess power that I can use later on AND also still have power if (or when, if current news reports about the electricity market are any guide) the grid goes down.

        I don’t really care about matters like ‘return on investment’ or ‘getting back my initial investment in savings’ – after all I am never going to get anything ‘back’ from the financial investment in a Smeg double-oven or that really fancy tap I like.

        I would just like to be able to say ‘yah boo sucks’ when the grid goes down and still be able to run the evap cooling so when a hot flush comes along I can stand under the vent and feel much better.

        Of course there IS a price point I could not go past.

        My only other concern is that lithium batteries can blow up – so where to put it?

        My new build has started – but perhaps I am six months or more too early to be able to do what I want to do?

        • Ronald Brakels says

          Hi Kim. If there is no hurry you can wait and see how the Powerwall 2 turns out and how other battery systems compare with it on price and function in the future. (If the Powerwall 2 works well there may be a considerable waiting list for it.)

          If you really want to be confident of having power during blackouts you can get a multimode (hybrid) inverter installed along with an auto-start generator. Batteries don’t have to be part of this system and it would be cheaper without them, but having batteries would mean your generator would only run during extended blackouts, which would be quieter, and it would need to be refueled much less often.

          With a sufficiently sized solar system you could go for weeks or longer without grid power.

          The risk of fire from a lithium battery system definitely should be low, but if you are concerned you can check that the battery system uses lithium iron phosphate batteries, which are the type least likely to catch fire. You can also install them in a low risk location such as a separate outdoors enclosure.

          • Ronald – you are such a brick for answering my queries – thank you. As the build is currently in progress I thought I should be able to get what I want as part of the build. I have a fixed price contract that includes a 4.5kw solar array. I was prepared to pay for the upspeck to add battery + blackout-ready capability.

            However I perhaps should just ensure the system installed is capable of such an upspeck in the future? Philosophically I don’t see the point of a generator if I am still making power from a solar array that can be used. So if I want the option to upseck later to what I want, is it enough that I ask the builder to install a system that is ‘battery ready” or do I need to specify more than that?

          • Ronald Brakels says

            My advice to people who are considering getting batteries in the future is not to spend money making their home ready for them now. Battery technology is rapidly changing and so any money spent now may end up being wasted. Batteries can be AC coupled to your home which will allow them to work regardless of what kind of rooftop solar system you have.

            Unfortunately, normal rooftop solar won’t be able to supply power during a blackout. It will shutdown as a safety measure to protect people working on power lines. It is possible to get a multimode inverter that will allow electricity from solar panels to be used during a blackout without using batteries, but this can be difficult, as not much power will be produced when the sun is low in the sky and clouds can greatly reduce solar generation.

  7. Please take out the ridiculous humor and you will have a great, informative write up. Why try to mix humor into something like this? If I want to laugh, I will watch a movie or comedy show, When I want to learn something, I don’t need 30 percent of the write-up trying to be funny. As a matter of fact, it never even made me smile once. It was annoying, so much, that I actually took the time out to write about it.

    • Come now, no need to be kill joy. I for one get a good laugh at Ronald’s humour.
      If you really want to read dry, boring technical articles call up the Elec Eng department at your local Uni and ask for access to their many mainly unreadable and certainly zero humour content PhD theses they have on PVs and batteries.


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