What Type Of Solar Battery Backup Do You Need?

In this video, Finn discusses the different types of home solar battery backup and what happens with each in a mains grid blackout scenario.


In the last video I went through the economics of batteries versus solar power. Batteries do not pay for themselves before the warranty is up at the moment – they’re not an economically rational purchase in Australia.

But what if you want the other benefits of batteries – and one of the big benefits is backup. What is that worth to you? Well, everyone’s different and you have to put your own price on it.

I’ve got a battery in my house and a few months ago the street was totally blacked out. I was cycling home and this is what I saw.

Blackout protection

Mine was the only house in the street that had its lights on and life carried on as normal for us for about two or three hours. It was awesome.

4 Levels Of Solar Battery Backup

So what’s that worth to you? Only you can decide, but if you do choose to buy a battery for the backup capability, it’s really important that you get the right kind of backup. There are four levels of backup – the following is terminology we’ve invented at SolarQuotes to show you how different the levels of backup power are in the batteries on the market in Australia today.

Level 0 Battery Backup

Let’s start with level zero. Level zero means you don’t actually get any backup. If the grid goes down, your battery stops working. There are plenty of batteries available that do that, believe it or not – avoid those batteries.

Level 1 Backup

Then there’s level one backup. These batteries will back up your home when the grid goes down, but they will reduce their output power. You might have a five kilowatt battery, so that is a battery that stores energy but its power rating is five kilowatts. When the grid goes down, it reduces its power to say 1.82 kilowatts. That’s not a lot for powering your home, so it’s a degraded performance when the grid goes down. Avoid those batteries.

Level 2 Backup

Then you’ve got level two backup. The grid goes down and your battery can pump out electricity at five kilowatts. It is the same power whether it’s in backup mode or it’s in grid-connected mode. I think you should avoid Level 2 as well and there’s a reason for that – they will not charge your batteries from the solar panels when the grid’s down.

Why won’t they do that? Because it takes extra electronics to do so. Say your solar power system is generating four kilowatts and the grid is not connected. Your house is using two kilowatts. Your battery is full, you’ve got an extra two kilowatts of solar power. It’s got nowhere to go because the grid is not connected. That means something’s going to catch fire or go bang unless you throttle back the solar panels.

Level 3 Backup

So you need extra electronics to throttle back the solar panels. If you want to charge your batteries from solar without the grid, that’s what we call level three backup. I call it apocalypse-proof backup, because in theory, if you’re careful with your electricity usage, you can go almost indefinitely on battery backup because the batteries will charge up from the solar panels as soon as the sun comes up.

If you haven’t got level three backup, once your battery’s flat and you’re not connected to the grid you’re out of power. So, if you’re going to spend thousands of dollars on a solar battery, get level three backup. To make sure you’ve got level three backup, here is what you say to the person selling you the solar.

“I want the solar panels to charge my battery when the grid’s down.”

… and you get them to write that on the quote.

If  you’re considering buying solar power and/or energy storage, check out Finn’s book – The Good Solar Guide – which is free to read online.

About Michael Bloch

Michael caught the solar power bug after purchasing components to cobble together a small off-grid PV system in 2008. He's been reporting on Australian and international solar energy news ever since.


  1. Rod Cunningham says

    Hmmm, I suspect Finn’s video does leave us in the dark! The inference is the backup smarts are in the battery. In most systems, the ability of the battery to provide back-up power and to be charged by solar panels when the grid is unavailable is generally dependent on the technology in the inverter. The suggestion that batteries will catch fire or explode is a little exaggerated!
    Several types of hybrid inverters in DC coupled systems actually provide a combination of Levels 1 and 3. (I cannot speak about the AC coupled systems)
    Goodwe and Growatt and other hybrid inverters will provide limited AC back-up power (2.3 – 3.6kw) during the absence of the grid and will continue to charge the battery from solar panels.
    We have a 5kw Goodwe GW5048-EM inverter with a 10kwh LG battery. Its 10A back-up output wont run the whole house but is adequate for lighting, to run the router and provide communications (bushfire warnings) and operate a fridge and sleep apnoea machine. So Finn, if we add Level 1 and Level 3 together, maybe there should be a Level 4.

  2. When I use the word ‘battery’ I actually mean ‘battery system’, which is the battery and battery inverter together.

    Good point – I should have said that explicitly.

    To see which hybrid inverters provide which level of backup you can use this table:


  3. Bret Busby in Western Australia says

    It is unfortunate that my comments about these issues, got censored out.

    Bad faith and bad form.

  4. Denis Redfern says

    I am retired and spend quite a bit of time at home, so it’s a different usage model to someone who goes out to work all day. I have a 9.3kW Solaredge system that will power the entire house including airconditioning when the sun is shining. I’d like to understand what’s involved in having a three phase system with a battery. I don’t necessarily want to run the airconditioning, but pretty much everything else to avoid having to rewire the house for a single phase of essential loads, which means it needs to be able to do 5kW peak to cope with having the kettle and the toaster on at the same time. I’d also like the system to fill in the peaks and troughs that happen when a cloud goes over, or for limited use in the evening

    • Because you already have existing solar edge system, unless you are planning of replacing that inverter, or have spare roof for extra panels, you will be limited to AC coupling for your battery. Unfortunately if you want “Level 3 Apocalypse” battery backup, 3 phase is going to be problematic with any existing 3 phase solar inverter.

      True 3 phase ongrid battery products that provide real 3 phase power are rare and complicated. I have seen products from Victron that technically would appear to be able to do this, but a while ago when I checked, those products were not approved for Australian grid connection, and they were expensive (they might now have approvel). From solarquotes table, it does look like the Fronius Symo Hybrid seems to claim to be able to do that if you read here https://www.solarquotes.com.au/blog/wp-content/uploads/2017/09/fronius_symo_hybrid_and_storage_solutions.pdf . But the devil might be in the detail here, because to do that I assume it would need to work around some of the existing AS4777 rules (or ignore them). But maybe it does in fact work. And if so this might be your way forward if you are happy to go for DC coupling your solar (ie ditch solaredge).

      However, just because you have 3 phase, does not mean you can’t go for backup on only a single phase with your battery. AC coupling will potentially allow it to work with your solar in a blackout, as long as you solaredge is only single phase and NOT 3 phase. But if your solar is single phase, then something like 1 or more Tesla powerwall 2 will do exactly what you outline as long as you only need to backup 1 phase (including offsetting all your power on the other phases to net your usage to zero when the grid is up and you have battery capacity). Yes, you will need to rewire everything you want backed up in blackout to the phase you are going to keep up with the battery. But this is usually a very simple and not expensive process of change the phases that the circuits terminate in the meter box. It is not rewiring the whole house. It is pretty standard to wire big and/or non critical loads so they are not backed up in a blackout. But even with this, under normal grid conditions, the battery can still supply these loads to reduce your grid usage.

      Put for me, if you are doing it for blackout protection, any product that does not support generator input is also limited as there are often periods when battery capacity + solar is not enough, and this is where generator input is required. Still with batteries like the Tesla PW2, generator input is still not available. So keep that in mind.

    • “Toaster and the kettle on at the same time……..”
      …..and while that’s going on I suppose you drive your 40-kilo kid to school in a 40-ton pantech?
      Why on earth would anyone set up a large, expensive solar system (including a massive battery-bank) in order to avoid making their coffee and toast one after the other?
      (or make their coffee on a small gas-ring?)
      (and/or, for that matter, reduce the solar-system by 75% and install a remote-start gas-powered generator, running for a few minutes, to run the jug and toaster?)
      I’ve been around for a long time, and can’t get past the idea that ‘alternative energy’ is all about not wastingf resources. (Based on the KISS principles.)

  5. Wayne Robinson says

    A few weeks ago, we had stormy weather in Perth, and the power went out for a few hours in a very limited area of my suburb (including my house).

    It was inconvenient, with not having lights until 8:30 pm. I had to use a torch. I wondered about whether it was worth the expense of having a backup battery.

    After the power went back on, my answer was ‘no.’ It wasn’t all that inconvenient.

    I don’t use all that power. The microwave is 700 Watts. The kettle uses 2 kW. The fridge when it’s running 300 Watts. Lights hardly anything. So level 1 seems almost good enough for me.

    I wonder what the difference in price would be between the various levels, in the unlikely event i decided to get a battery system.

  6. Tony Tucker says

    Have been wondering about potential for increased viability of batteries since I read Richard Chirgwin’s article (Dynamic Solar Export Limits: SA’s Smart Way To Integrate More Solar, 3 October). If I read that correctly, & if it actually goes ahead, the grid may lower your solar system’s input to the grid at times of grid surplus, with a consequent loss of FiT. Obviously the reduction would usually occur at times of peak household solar production. again subject to my understanding wouldn’t that increase viability of batteries and increase payback periods for solar systems generally?

  7. Malcolm Colless says

    We have a SolarEdge HD-Wave Inverter, a Sunny Boy (SMA) Storage Controller and an LG Chem Resu 10H battery with 8kw of panels. Our first blackout occurred at 8am in the morning during a rainy period. The battery was fully depleted so it gave us nothing and it did not charge from the panels because of the weather. Previously we had a separate backup battery (lead-acid) which we manually switched over to when required and supplied us for a day or two. We got rid of this system when the batteries wore out, but now we believe we should have rejuvenated it for situations like the above.

    We run our house on tank water, which means when there is blackout the tank pump draws about 7kw for a mini second as it starts up when we turn a tap on. This causes the battery to shut down because it only allows 5kw output. We need to transfer to town water to prevent a shut down happening. There is room for considerable improvement in such systems still.

    • …..or you could ~ for next to nothing ~ use gravity as your power-source by sticking your tank on a tankstand. Run the (12-volt) pump to fill it when the sun shines, and NEVER need to use the pricey/pricey-to-run pressure-pump again.
      I imagine the olde-timey rules still apply: a 12-foot high tank-stand will provide ‘mains’ pressure. (Or depending on your situation shift your tank up the hill a bit.)

      • ps: a handy and cheap LARGE water reserve on standby is a good idea. Until I was able to access the creek about 300 yards distant I collected roof-water in a 2nd-hand 20-foot above-ground swimming-pool ($35 from ebay) erected on an old roll of carpet and covered with a colourbond lid ~ also recycled.
        Among other things it meant I could get away with a small (500-gallon) header-tank and a much less complicated tankstand.

  8. Dave Wilson says

    I have the Tesla2 PW. It has been installed so the backup feature provides the whole house. I have had one grid fail and the transfer to battery was seamless.

    How do I know this has happened so I can limit my usage? Is there something I can have installed to let me know?


    • This was a question I asked myself. I believe the App is supposed to notify you, but believe this has in the past been hit and miss.

      My ideas :-
      1. get you light circuit (or any other circuit that you would notice not being on, but not critical if it goes out for a short period of time) wired so it is on a manual transfer switch that gives you the option of changing between backed up and no backed up circuit. Generally leave the lights in the non backed up position. Then when the power goes out, your lights will go out, and give you a very visible indication that the power has gone out. You can then go out and manually flick the switch over to backed up so you can have lighting till the power comes back. Now you might point out that that during the day, you might not notice the power out because you are not using the lights?? But in truth when this happens, your solar should be producing and thus limiting the dangers of battery depletion if your solar is big enough.

      2. A while ago I brought a rechargeable LED “Auto work light” from Aldi (I am sure you could buy similar elsewhere). Similar to this http://offers.kd2.org/en/au/aldi/pSEL/. This has a feature called “Emergency light function”. ie when the light is in the charger, and there is power to the charger, the light is charging and the light is off. When the power goes out, the light automatically comes on. If this was plugged into a non backed up circuit, this would come on and give you an obvious indication that the power has done off. This would probably work well day or night as long as someone was around in the room where the light was located. Quick search to see if I can find similar for sale now on ebay turned up this. https://www.ebay.com.au/itm/RECHARGEABLE-60-LED-720L-LIGHT-TOWER-STRIP-LAMP-W-EMERGENCY-POWER-OUTAGE-AUTO-ON/323797454550?hash=item4b63d50ed6:g:1REAAOSwwjhczbLx

  9. “That means something’s going to catch fire or go bang unless you throttle back the solar panels.”
    This doesn’t sound correct.
    Since most residential PV systems have a higher rating on the panels than on the inverter, the inverter will already be performing the ‘throttle’ function. This is a function of the inverter, not of the battery.

    • Michael’s point about the issues with Level 2 batteries and needing extra functionality to be level 3 batteries is 100% correct. Though you could argue about if something is going “to catch fire or go bang”.

      Bigger solar panels than the invert is absolutely no problem, in just the same way as there is absolutely no problem putting a bigger battery in a device than it needs. The inverter can only use as much as it really needs.

      Grid connected solar inverters work on the assumption that that they are ALWAYS grid connect or shutdown because the grid is down. They are also designed to export export as much power as they can generate. The only way they can export power is to keep raising voltages until their voltage is high enough above the grid voltage to export max power.When you isolate from the grid, and if you want to keep solar PV running that can only assume it is grid connected, you need to take responsibility for managing all supplies and loads to make sure everything is balanced. If you don’t do this, and there is too much supply, what you will see if voltage rise and voltage spikes. Best case scenario is that the inverter shuts down due to over voltage before anything else in your house goes bang. But you can’t count on this at all, because while all grid tied inverters must shutdown in various over voltage events, for stability of the grid and other reasons, this will not happen quick enough to avoid potentially damaging voltage rises and spikes. So this should not be counted on.

      This is why Level 2 batteries will NEVER be connected to allow grid connected solar to run at the same time. And exactly why you can’t just hook your generator to your house to bring the solar back up in a blackout without risking damage to the things in your house.

      Level 3 batteries overcome this with extra circuits and programming to overcome these problems. Eg in blackout mode, they will typically do things like :-
      1. They will use a thing called “frequency shifting” to use mechanisms required in all grid connect solar systems to shutdown or throttle down when the frequency rises. This feature in grid tied inverters is nothing to do with batteries, and is mandated in all Australian grid tied inverters to support the stability of the grid. But batteries can use the same feature to their benefit.

      2. Point 1) above would not be enough on its own to manage supply and demand because frequency shifting of output in solar PV would be too slow to prevent problems in the short term. To overcome this, the battery is designed so it can soak up the excess generation for short periods of time by charging the battery, for the time it takes to throttle back solar. This is why any good battery design will limit the size of AC couple solar that can be supported in a blackout. It needs to be less than the short term charging capacity of the battery to ensure it can always handle whatever excess power there might be. It is also when a well designed isolate battery will never allow itself to be charged to 100% during a blackout.

      As to what happens and if things catch fire or go bang, this will depend on a lot of things. ie at what voltage the solar PV runs out of puff and refuses to push dangerous voltages, and how sensitive to spikes and other high voltage events all the equipment in your house really is. But what we do know is the voltage spikes and high voltage is NOT good for product longevity and will reduce the life of lots of electrical appliances and should be avoided.

  10. Have you been reading my mail?? –> (I’ll refrain from the ‘D’OH!’
    “If you want to charge your batteries from solar without the grid, that’s what we call level three backup. I call it apocalypse-proof backup, because in theory, if you’re careful with your electricity usage, you can go almost indefinitely on battery backup because the batteries will charge up from the solar panels as soon as the sun comes up.” (and/or other options.)
    The next step is ‘Level three A’……dumping the grid altogether. Thatr includes the insidious ‘service charge’. I note some of your corresponents are citing a ‘service -charge’ of as much as 90 cents. The last time I was on the grid (2015 ~ and purely for the 66-cent FIT), Origin was charging $1.76 per day, although I was living (literally) within rifle-shot of the major power-plants of the LaTrobe Valley.

  11. ps… the inverter question is another that has a multitude of options availlable.
    Nobody with more than three braincells (in the days when huge inverters cost half the price of a new car and were as efficient as a new car with square wheels) opte for several small inverters running diferent circuits….. and a heavy VDC cable which could be tapped along its length to run stuff that would run on VDC. KISS principles in action.

  12. There’s another aspect of backup, being how quickly the alternate power supply cuts in once the grid goes off-line.

    i. Some systems are nearly UPS level and available within milliseconds such that for all intents and purposes the supply has no interruption and all devices remain on.

    ii. Some take a few seconds and the interruption is long enough that many electronic devices will require re-setting once power is restored (in fact these 1-3 second outages can be more of a PITA as often electronic devices don’t reset properly when there is such a short outage but they do if the power was off for 10+ seconds).

    iii. Other systems may require around half a minute or so before they will cut over to battery power (sort of a similar time frame to auto start generator systems).

    Some provide i, but not always and can revert to ii.

    While i. is pretty nice, ii. or iii. are fine if you combine with small portable UPS device for key electrical devices (e.g. NBN connection/modem).

    Then there is what to do when you have 3-phase.

    Backup options are a bit more of a challenge in that environment, and getting cutover time level (i.) is going to be prohibitively expensive I’d have thought if you need to cover supply on all three phases (even if limiting the circuits to be supplied).

  13. BTW, for back up in our grid outage prone area, I’ll be setting up a generator with cutover switch. Straightforward tech, not all that expensive, reliable and will run for as long as I supply it with fuel. We’ve had 33.6 hours of outages inside the past year, with multiple (~20) occurrences. Previous years I don’t have the stats but my sense is the frequency of outages was about the same. It was very noticeable after moving from the city where outages were rare.

  14. I would just like my solar to work as Ausnet supply’s overvoltage my system shuts down at 9:30am till 16:00. If I install battery’s is there any advantage installing battery’s to maybe smooth the voltage considering my supply voltage is around 260 volts

    • Maybe, but probably not. But the real answer is very complicated and depends on the reason for the over voltage and how big it is, what inverters and batteries you have etc etc etc. What is a complicated answer becomes even more complicated if you have 3 phase. So complicated in fact that my advice if you have voltage issues with solar is to get them fixed before you waste even more money on a battery which might have just as many issues.

      If your voltage is persistently at 260v you should be able to get this fixed by your provider (especially if you have record of this persistently happening when your solar is not generating). If this is the case, they really do not have a leg to stand on. To deal with over voltage issue your 1st point of call is to your electricity provider in your area. They have obligation to supply electricity to your place under normal conditions at voltages WELL less than 260v (varies by distributor but it probably should be below 253v under “normal” conditions). If they are not doing that, their obligation is to tap the voltage down which should fix the problem for you. When you raise this, they will probably try and blow you off. But be persistent and knowledgeable and hold them to account. If you do this, they should measure the voltage at your point of interconnect. And if it is above their specification they really need to fix. If however on their long term (be careful, they might try and blow you off with a short term measurement and suggest it is only to do with solar and there is nothing they can do and all sort of other bs excuses) voltage monitoring is within the spec, and the “voltage rise” is coming from the line in to your property, then that is your problem. If so, you might need someone to investigate that wiring. Look for bad connections, or it could be that the wire to your house is too small or too long for the loads in which case you might need to size up to address it. But you can get an idea on where the problem lies by measuring voltages with solar running and full blast and turning it off and measuring the voltage. The difference should be less than 2%.

      As for if the battery will help?? If the battery can reduce the amount of current that you solar pushes up the line, this will reduce the voltage rise due to solar export, and might help your solar keep running a little longer. But I would not expect big gains from this for lots of reasons. eg 1) when the battery is full, it won’t help at all 2) if you have 3 phase, and the battery is helping to offset usage on other phases, it might made the problem worst at times of discharge 3) inverters on solar PV and I assume also on the battery probably should not start if voltage is over 253v 4) I assume the battery inverter also needs to shutdown and throttle on similar voltages to solar PV inverters (though I have not seen these values as commonly specified so maybe the rules makers have given them some dispensation that i am not aware of). Long and short it is that battery is almost certainly not the answer to your problems if you have over voltage issues.

  15. Chris Blair says

    Backup generators are part of the decision matrix when planning for blackout scenarios.

    Would be helpful if Finn and the team could include some basic education on our options.

    Thanks for comments

    • Probably not nearly toffee-nosed enough for this forum, but ->
      Go to the local wrecker and get a 100-amp (give or take) alternator out of the vehicle of your choice. This will have a regulator built in.
      Take it home and bolt it to a plank, and bolt a conveniently-laying-about engine to the other end of the plank. (old lawnmower,chainsaw/compactor/stationary-engine of any sort) Connect them with pulley/fan-belt/whatever (the wife’s panty-hose will work) and away you go.
      My engine-of-choice was the luggy old concrete-mixer engine, which could be left on the mixer and the large (efficiency-producing) fly-wheel used as a pulley to run the alternator. (or olde-timey automotive generator if you know what you’re doing.)
      Once it settles down this will run on about half-a-pint of petrol per hour. Some were diesel, and they could be run on home-prduced (depending on your situation) bio-fuel.
      Wouldn’t run a power-station ( and might struggle with a toaster), but will get you out of trouble on a short-term-basis.
      (If necessary, a variety of devices can be chucked together to mostly muffle the noise.)

  16. Stephen Jenkins says

    Hoping you can tell me how to get a supplier and installer to actually come back to rectify problems with the system they have supplied and installed. Unfortunately for my next door neighbor had a solar and battery installed and I was looking at it one day and noticed it had am alarm on it (BMS failed) and the power out put was only 425 watts while the smaller system on my roof was around 2.5 kw. They have not been able to get the installer to come out and see what the problem is over the last 3 months

    • Ronald Brakels says

      If the solar and battery isn’t working as it should and they haven’t had a response from the installer in three months that is definitely a consumer affairs issue. I suggest they contact consumer affairs in their state. If after getting assistance the installer still doesn’t respond they can be taken to a consumer tribunal or court. While I am not a lawyer I am certain they will be required to either bring the system up to a properly working state or, if they can’t do that, remove the entire system and refund their money.

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