Retrofitting battery storage to an existing solar PV system: What to consider

Lots of Australian homes are expected to install battery storage in the coming years. Many of these homes will install brand new solar-plus-storage systems, but quite a few will be retrofitting batteries onto a pre-existing system. What do you need to keep in mind for a battery storage system retrofit?

New: Check out our decision-making helper tool for expanding an existing solar system with panels/batteries!

Solar System Expansion Helper

Considerations for retrofitting energy storage to your existing PV system

  • Are you the recipient of one of your state’s generous feed-in tariff rates? If you currently receive a generous rate for the solar electricity you export to the grid under a state-mandated feed-in tariff program (nearly all of which are now closed to new applicants), it may not be worth your while to install batteries.
  • What proportion of your electricity consumption does your existing solar system meet? Depending on when you had your system installed and whether or not you have/had a feed-in tariff, your system may only generate enough power to meet a small portion of your electricity needs – or it may generate more than you actually need. This will dictate the best approach for sizing your battery storage. Speak to your installer about how to retrofit a system to optimise value.
  • What energy storage system size would best suit your needs and budget? Do you want to go off-grid at all costs (possibly to spite your utility), or do you view energy storage as an investment to complement your solar PV? Your answer to this question will help you determine the optimum system size. (If you want to explore your options in further detail, check out our Battery Storage Sizing & Payback Estimator tool.)
  • Do you want a ‘one box’ or ‘two box’ battery storage solution? There are essentially two ways to install batteries on an existing solar system:
    • 1) replace the existing inverter with a hybrid inverter (which does both batteries and PV) – the one box solution, or
    • 2) install an additional inverter (or ‘all-in-one’ battery product that has its own, in-built inverter) to handle the batteries separately – the two box solution.
    • (N.B. Enphase’s AC Battery could fall into a 3rd ‘multiple box’ solution category – it is a modular, retrofit-friendly battery with a built-in inverter).
      • Speak with your installer about which option is the most economically attractive and which will provide the functionality that you’re most interested in.
  • Will the system provide you with back-up power? This is not a given with battery storage systems. Only certain battery storage systems will allow you to access your battery power when the grid is down – make sure you ask.
  • Should you install batteries now, or just get a battery-ready inverter? If your system is over 5 years old and due for an inverter replacement, this might be a good time for you to consider installing energy storage – or perhaps just a battery-ready, hybrid inverter. Even if you don’t install batteries right away, a hybrid inverter will ensure that batteries can easily be installed at a later date.
  • Check out some battery retrofit case studies for Sydney
  • Check out some battery retrofit case studies for Brisbane
  • Need more advice? Give us a call on 1300 78 72 73. Our services are 100% free to our customers.


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Jeff Sykes


  1. I had a 5.13 KW Solar Panel system consisting of 18 x 285 LG LG285S1C-L4 panels with a Fronius Primo 5.0-1 inverter installed in September 2016. I am contemplating adding battery storage.
    Is the Fronius Primo 5.0-1 inverter compatible with a battery install or would I need to purchase an additional inverter? Would I also need to install additional panels? Current consumption is around 16kWh per day & ideally I would like back up power capability as well.What would be the approximate cost in Adelaide?

    1. Hi Terry,

      Fronius’ ‘hybrid’/battery-ready inverters are those of the Symo range, which means you would need an additional inverter to handle the batteries – or a battery solution with an inverter built in (all-in-one).

      As a very rough guide, 8-13kWh of storage capacity would probably do the trick for you. A Tesla Powerwall 2 is an all-in-one 13.2kWh package, while LG Chem offer have batteries that you can mix-and-match for a range of sizes (they work with a range of popular inverter brands). For pricing, feel free to request a battery quote comparison through our system by filling out the form on this page.

  2. Hi, I have a 4kw systemon my roof and ZeverSolar Evershine TL5000 single phase invertor.
    What would it take to retrofit a battery storage system and what would it cost me ??

    1. Hi Stephen,

      Your current inverter is most likely not battery-ready, which means you’d need to either replace it with a hybrid inverter or have a second, separate battery inverter installed as a retrofit.

      As for prices, we’d recommend getting some quotes, which you can do by filling out the Quote Comparison request form to the right of this page (select ‘Battery Only’ as you already have an existing solar system).

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