Existing solar
Adding a battery to solar you already have
If you've had solar for a few years, you've probably noticed you export a lot during the day for very little and still buy power every evening. A battery fixes that. How you add one depends on the inverter you've already got.
Option 1: replace the inverter with a hybrid
A hybrid inverter runs your panels and a battery from the one box. For most older systems this is the cleanest upgrade: the old inverter comes off the wall, the hybrid and battery go in, and your existing panels connect to the new inverter.
It's often the right call when the old inverter is getting on. Inverters usually wear out well before panels do, so if yours is 8 or more years old you may be paying to replace it soon anyway.
Your panels need to be checked first. The installer has to confirm the strings suit the new inverter's voltage and current limits, and that the isolators and cabling are in good condition. Older rooftop isolators in particular are worth a close look.
Option 2: keep the inverter and add an AC-coupled battery
An AC-coupled battery has its own inverter built in and connects alongside your existing system. It's the usual choice when your current inverter is fairly new or when you have microinverters.
Under the rules that started on 1 May 2026, every inverter on the property has to be controllable as one system. Energy Policy WA calls this "whole of site compliance". In practice that means either a small gateway device that manages both inverters, or a new inverter that can control the old one (sometimes called parent-child mode, usually only between the same brand).
What happens to your buyback
This is the part most people don't get told.
- If you're on the Renewable Energy Buyback Scheme (REBS), Synergy pays a flat 7.135c per kWh for exports. Synergy's own terms say that if you change your system, you may not be able to stay on REBS.
- The newer scheme, DEBS, pays 10c between 3pm and 9pm and 2c the rest of the day.
With a battery, that switch often doesn't cost much. A battery soaks up the midday surplus you used to export, so you export less in the middle of the day. Anything you do export in the evening earns 10c instead of 7.1c. But it depends on your usage, so we look at your bill and ask Synergy rather than guessing.
Some people still talk about "losing the 40c". The old state feed-in tariff of 40c (later 20c) closed to new applicants in 2011 and paid for ten years, so it has finished for everyone. If your bill shows a buyback of around 7c, that's REBS.
Rebates on an upgrade
- The battery earns the full federal battery discount, the same as on a new system. See our rebates guide.
- Your existing panels already claimed their certificates when they went in, so they don't earn any again.
- New panels you add do earn certificates.
- A replacement inverter on its own earns nothing.
A quick check before you get quotes
- Is your current system working properly? Look at the inverter's screen or app around midday on a sunny day. If it's making far less than its size suggests, or showing fault codes, sort that out first. A battery won't fix a failing array.
- Find the inverter's model and age on the label on its side.
- Count the panels, and note the wattage if you can find it.
- Download your usage data from Synergy's My Account. A year of half-hourly readings is the best way to size a battery.
Want the numbers for your house?
Send us your latest Synergy bill and we'll size a system from your actual usage, show every rebate as its own line, and tell you what we can and can't offer before you sign anything.