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

by Solar Choice Staff on May 29, 2017

in Installation advice,Solar System Products,Batteries & Energy Storage

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?

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 Retrofit 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 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.
  • Need more advice? Give us a call on 1300 78 72 73. Our services are 100% free to our customers.

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{ 2 comments… read them below or add one }

Stephen Graham May 21, 2016 at 12:25 pm

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 ??
Thanks.

Reply

Solar Choice Staff May 30, 2016 at 10:49 am

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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