Adding a battery to your existing solar

Yes, you can usually add a battery

Most people asking about batteries already have panels on the roof. A battery can be added to most existing solar systems. The question is how.

It comes down to one box on your wall: the inverter. That is the unit, usually near your switchboard, that turns the power your panels make (called DC, or direct current) into the power your home runs on (AC, or alternating current). A battery stores DC power too, so it also needs an inverter. You can either give the battery its own, or replace your old inverter with one that handles both.

Option 1: keep your inverter and add a battery inverter

This is called AC coupling, because the solar inverter and the battery inverter meet on the AC side, at your switchboard. The government's Solar Consumer Guide says that when you add a battery to an existing system, you can usually keep your existing solar inverter, and that AC coupling is the usual arrangement. Some batteries have the inverter built into the same cabinet.

What is good about it:

• It does not need to match your old system. The battery runs alongside your solar rather than plugging into it.
• It works with microinverters. If you have a small inverter under each panel rather than one box on the wall, a battery with its own inverter is the option that fits.

The downsides:

• It is a little less efficient. Solar power is converted from DC to AC, then back to DC to charge the battery, then to AC again when you use it. Each step loses a bit.
• Two inverters on the wall. Your old one keeps ageing, and when it fails you replace it separately.

Option 2: swap to a hybrid inverter

A hybrid inverter does the job of a solar inverter and a battery inverter in one unit. The panels and the battery both connect to it on the DC side, which is why this is called DC coupling. To add a battery this way, the old inverter comes off the wall and the hybrid goes in its place.

What is good about it:

• Fewer conversions, so it tends to be more efficient than an AC coupled battery.
• One inverter running the panels and the battery, instead of two.
• A fresh start if your old inverter was near the end of its life anyway.

The downsides:

• More work up front. You are paying for a new inverter as well as the battery.
• It does not suit microinverters. Hybrid inverters cannot connect to a microinverter system.
• Your panels have to suit the new inverter, which your installer checks when they design it.

How to tell which suits your home

On inverter age: the Solar Consumer Guide says string inverters typically last 10 years or more, but are likely to need repair or replacement within the life of your panels. If yours is already showing its age, paying to keep it and add a second inverter can mean paying twice.

Export limits from your network

The company that runs the poles and wires in your area (your network, or distributor) sets limits on how big an inverter can connect and how much power you can send back to the grid. If your system has an export limit, anything your panels make above it is simply wasted. A battery can soak up some of that instead. Either way, the design has to fit inside your network's limits, which your installer checks.

Old premium feed-in tariffs

This is the one that catches people. Some households are still on generous government feed-in schemes from the early 2010s, and changing the system can end them.

• Queensland's 44c Solar Bonus Scheme runs until 1 July 2028. The Queensland Government says you lose it if you increase your inverter capacity, replace your inverter with a larger one, or use a battery while the 44c system is operating, unless the battery has a separate network connection. Using a battery only when the solar is not running, at night or in a blackout, is allowed. It says to check with your distributor before adding batteries.
• South Australia's 44c distributor feed-in tariff is paid until 30 June 2028 for systems installed, or approved to connect, before 1 October 2011. Check with SA Power Networks what changes are allowed before you add anything.

With both schemes ending in 2028, some households are better off waiting and adding the battery when the tariff finishes. It is worth doing the sums on both before you sign.

Does the rebate apply to a battery added to existing solar?

Yes, it can. According to the Clean Energy Regulator, a battery added to existing solar can earn the federal Cheaper Home Batteries discount when:

• The battery is on the Clean Energy Council approved list and is between 5 and 100 kWh of nominal (total) capacity.
• The inverter it connects to is capable of joining a virtual power plant. You do not have to join one, it just has to be able to. If you are connecting to a hybrid inverter you already have, it must be on the approved inverter list now, or have been on it when your solar was switched on. If it is not, it has to be replaced.
• Your existing solar meets your state's electrical safety rules. It does not need to be on the approved list itself.
• It is installed by an installer accredited by Solar Accreditation Australia with a battery endorsement.
• It is the first battery at the address to claim. Only one battery system per premises gets the certificates. You can add capacity to an existing battery only if that battery never claimed them and you add at least 5 kWh.

How much the discount is worth depends on the battery's usable size and the install date. We break that down in The 2026 home battery rebate, explained.

What we need to know before quoting

A good retrofit quote starts with your existing system. Have these ready:

1. Your inverter's brand, model and size. A clear photo of the label on the side is perfect.
2. Your panels: how many kW, roughly how old, and which way they face.
3. Microinverters or one inverter on the wall. If you are unsure, a photo of the inverter area helps.
4. A photo of your switchboard and meter. Some switchboards need upgrading before a battery can go in.
5. Where the battery could go. There are strict rules on placement, including the wall it mounts to and distances from living areas, doors and windows.
6. Your feed-in tariff and retailer, especially if you are on an old premium rate.
7. Your usage data. Half-hourly data from your retailer's app shows what you use after dark, which decides the battery size. See How big a home battery do you need?

When adding panels first is the better step

A battery only helps if your panels make more than your home uses during the day. The Solar Consumer Guide puts it plainly: it does not make sense to install one for a small rooftop system. If you have an older, small system that rarely sends much to the grid, a battery may sit half empty most days.

In that case the better step is often more panels first, or a new, larger system with a hybrid inverter and battery installed together. The guide also warns that for many homes the cost of a battery may outweigh the savings. Under the rebate program, whoever sells you the battery has to give you a written statement of the expected payback and savings, so ask for it and read it.

How Sunnn handles it

Sunnn designs and quotes systems using Fox ESS hybrid inverters and batteries, and arranges installation through accredited installers. For an existing system we start with your inverter, panels, switchboard and feed-in tariff, then tell you which route makes sense. If you want the battery to trade automatically on a wholesale plan with Sunnn+, it needs to be a brand Sunnn+ works with: Fox ESS, SAJ, Sungrow, Deye, Sunsynk or Tesla Powerwall. Check your battery.

Your next step

See what a battery could do for your home with the savings calculator, or check your eligibility and send us a photo of your inverter. We will tell you which option suits your system and show the rebate as a line on the quote. Savings figures are modelled estimates, not guarantees.