AS4777 and battery rebates for older solar
Adding a battery puts an older solar system back under review. The federal discount asks that the existing system complies with state electrical safety regulations. A hybrid inverter faces one extra test. The WA rebate applies today's standards to the whole site, including AS4777, the standard for connecting inverters to the grid. An older system can still qualify for both, though it may need parts replaced before the battery goes in, most often under the WA scheme.
What AS4777 covers
Part 1 of AS4777 (formally AS/NZS 4777) governs how an inverter system is installed. Part 2 governs the inverter itself: how it reacts to voltage swings, when it disconnects, and which grid settings it carries. Western Power requires the "Australia Region B" setting at commissioning, so an installer connecting new work confirms it.
Part 2 is the part that reaches the rebates. The Clean Energy Council (CEC) keeps a list of approved inverters that follows the current edition of the standard, and any inverter installed with the battery has to be on it. An inverter can be compliant on the day it goes on your wall and drop off the list years later, which matters when the new battery will plug into it.
What do the rebates require of an existing system?
The federal rule is narrow and the WA rule is wide. Federally, an existing solar system must comply with state electrical safety regulations, and its panels and solar inverter do not need to be on the CEC list today. Nothing in the federal rule calls for a whole-site upgrade.
A hybrid inverter you already own (one unit that runs both panels and battery) faces a stricter test if the new battery plugs into it. That inverter has to be able to join a virtual power plant (VPP), a scheme where batteries are remotely coordinated to support the grid. It must also be on the CEC list now, or have been when your solar was commissioned. Fail either and the inverter is replaced with a listed one.
The WA Residential Battery Scheme calls its test whole of site compliance. Your existing system has to work with the remote management a virtual power plant needs and meet current electrical standards. The state government's guidance is that parts of the system or its wiring may need upgrading, that some applicants will need a full replacement, and that the older the system, the more likely either becomes.
Where an older system falls short of today's standards
Inverters installed before 18 December 2021 did not have to meet the 2020 edition of AS/NZS 4777.2. One from that period may lack the Australia Region B profile that edition added, whose settings ease the inverter's output as grid voltage climbs. It may be off the CEC list too. On 23 August 2025 the list dropped every inverter whose manufacturer had not declared it compliant with Amendment 2 of the 2020 edition. Remote management is the other gap.
| Part | What an older system may have | What the rules now require |
|---|---|---|
| Rooftop DC isolator (the switch beside the panels) | A switch certified to the lower level allowed before mid-2018, or one of the recalled brands. WA's electrical safety regulator names these isolators as the main cause of solar system failures and the source of many fires | Level 3 safety certification, required in WA from 30 June 2018 |
| Switchboard | Circuits with no safety switch (RCD), and no labelling | The 2018 Wiring Rules, published 26 June 2018 and compulsory for WA installations built after 1 January 2019, require safety switches on final circuits in new and altered homes, and a labelled board |
| Earthing | Metal building framework that was never connected to earth | The same Wiring Rules extended earthing to all conductive building framework |
Left alone, an existing system does not have to meet the newer rules, but adding a battery counts as an upgrade under the Western Power rules that began on 1 May 2026, with or without a rebate.
What an installer checks on an older system
Under the WA scheme the battery must connect through equipment on Synergy's Supported Solutions List. A non-hybrid solar inverter cannot take a battery directly, but it can stay. An AC-coupled battery brings its own inverter and a gateway device and sits beside the old one, provided both new devices are on Synergy's list and the gateway supports your existing inverter as well as the new battery. Our retrofit guide sets that route beside a hybrid inverter swap.
Battery position is set by AS/NZS 5139, one of the battery installation standards in force this year. A garage wall that backs onto a bedroom can need a non-combustible barrier behind the battery.
The installer signs off on the whole site
Compliance sits with the installer. A Solar Accreditation Australia accredited installer has to install or supervise the battery, and the new battery and any new inverter must be on the CEC approved lists on the day they go in. Non-compliant work earns no federal discount. WA pays its rebate directly to the approved vendor and audits installations after payment.
A vendor wants the whole site up to standard before claiming, which is why one quote for a house includes a new switchboard and inverter and the next does not.
If a quote says your system must be replaced
Sometimes that is correct. The WA government tells applicants to shop around when a quote includes expensive replacements, or says the existing system makes them ineligible, and to check they are not being sold equipment they do not need.
Ask each installer to list what fails and which rule it fails against. "Your inverter is too old" is not an answer. "Your inverter is not VPP-capable and not on the Supported Solutions List, so the battery needs its own" is. Get the list in writing and hold it against two or three quotes. Scheme rules beyond the existing system are in the eligibility checklist, and the rebate amounts are in the post on how the federal and WA rebates stack.
This is general guidance, not electrical advice. Only a licensed electrician who has inspected your system can confirm what it needs.
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