Hybrid inverter or AC-coupled retrofit: how to add a battery to solar you already have

The two ways to add a battery to solar you already own

A battery is direct current. Your panels make direct current. Your house runs on alternating current. Somewhere in the system a box has to convert between the two, and where that box sits is the whole difference between the two designs.

In the hybrid design, also called DC-coupled, one new inverter does everything: it takes the panels on one side, the battery on another, and the house and grid on the third. Your existing solar inverter is removed. In the AC-coupled design, your existing solar inverter keeps converting the panels' output to AC exactly as it does today, and a second unit, a battery inverter or an all-in-one AC battery, sits on the house wiring and charges from that AC, converting it back to DC to store and to AC again to use.

Both are legitimate, both are eligible for the federal battery discount, both are installed on the Coast every week. They are not interchangeable, and which one suits your house depends on things a phone quote cannot see.

How each one actually works, and where the energy is lost

The difference is easiest to follow by counting conversions.

When AC-coupled is the right answer, including when it is the cheaper job for you

I will say this plainly because a lot of installers will not: sometimes the right answer is to leave your inverter alone, and that is the less profitable job for me.

Your inverter is young and good. If it is under about five years old, from a manufacturer with real Australian support and still under warranty, replacing it with a hybrid means throwing away a working asset you paid for. An AC-coupled battery keeps it, and the small efficiency penalty is the price of not buying an inverter twice.

You are on the 44 cent Solar Bonus Scheme. The scheme's conditions are specific: you keep the tariff if the inverter is replaced with one of the same or smaller capacity, you lose it if inverter capacity is increased, and a battery is allowed provided it is only used when the solar system is not operating, or it has its own separate connection. A hybrid replacement is almost always a bigger inverter than the 2011 original, and it ends the tariff. How a particular battery configuration is treated under those conditions is a question to settle with Energex and your retailer in writing before you sign, not after. On a house that exports a lot, the tariff is worth real money until it expires on 1 July 2028, and the honest design conversation is about how to add storage without breaching the conditions, or about timing.

The house does not want the disruption. A hybrid swap touches the roof wiring, the inverter position and the switchboard in one visit. On some houses, a heritage roof, a difficult inverter location, a job that has to be done live around a home business, the AC-coupled path is simply the smaller intervention.

SolaX build AC-coupled retrofit units for exactly this case, which is one reason they are in our range; the details are on the SolaX page and in the SolaX battery review.

When the hybrid swap is right

Your inverter is old or unsupported. Eight years or more, out of warranty, a brand that has left the Australian market, or already showing the afternoon shutdowns and morning faults I describe in what fails on a solar system after ten years. Replacing it with a hybrid turns a repair bill into the foundation of a modern system, and it is the most common battery job I do.

You want backup that actually works. A hybrid with a proper emergency supply output, or a system with a built-in bypass, keeps the panels charging the battery during an outage because one box controls both. That is the backup most people picture when they say the word. What it can run, and for how long, is a load and switchboard question, and I cover it in whole home versus essential circuit backup.

You want more panels. A 2014 system was sized for the tariff and the budget of 2014. If you are adding a battery, you almost always want more generation to fill it, and a hybrid swap is the natural moment to add panels, which also earns the rooftop solar certificates on the new panels. An AC-coupled battery adds no panels and earns no solar certificates; the federal battery discount applies either way.

Inverter capacity on your connection. Energex counts every inverter on the property against the same limit, 10 kilowatts on a single phase supply and 30 kilowatts across three phase. An existing 5 kilowatt solar inverter plus a 5 kilowatt battery inverter uses the whole single phase allowance, and a bigger existing inverter can leave no room for a separate battery inverter at all. A hybrid is one box, so on a lot of single phase houses it is the only design that fits inside the limit with any room to grow.

Three phase houses. If you have three phase supply and a single phase solar inverter on one leg, the hybrid swap is the moment to move to a three phase inverter that balances the house properly. Our three phase systems are built around that case.

What both paths have in common: Energex, the rebate, the switchboard

Energex. Any change to the inverter on your connection, and any change to battery capacity, is a connection application lodged by your electrician through the Energex Electrical Partners Portal before the work is done. That is true for a hybrid swap and for an AC-coupled battery inverter alike. A quote that does not mention the application is missing a step.

The federal battery discount. The Cheaper Home Batteries Program applies to a battery installed with a new or an existing solar system, so both designs qualify, and the discount is calculated on the battery's usable capacity, not the number on the box. I explain the structure, without quoting a figure that will go stale, in the federal battery rebate explained. What you should know for this decision: it steps down on 1 January 2027, and it does not care which coupling you choose.

The switchboard. Both designs need space on the board, protection for the new circuits, and, if backup is included, the changeover arrangement and the circuit protection that goes with it. On a 1990s board that is the hidden cost that makes two battery quotes differ by thousands, and it is the same cost whichever coupling you pick. What a switchboard upgrade costs on the Sunshine Coast has the general ranges.

Warranty registration and usable capacity. Whichever path you take, the battery warranty is generally conditional on registration within a set window after installation, and the capacity you should be comparing is usable, not nominal, because that is what runs your house and what the discount is paid on. What size home battery you actually need is the sizing guide.

Getting it quoted both ways: the questions to ask

Ask any battery installer these six things and you will learn more from the answers than from the price.

Which coupling is this quote, and why that one for my house? What is the total inverter capacity on my connection after the job, and does it fit the Energex limit? If the power goes out, will the panels keep charging the battery, and what exactly will it run? What happens to my existing inverter and its warranty? What is the usable capacity of the battery, not the nominal? And has the Energex application been included?

An installer who can only answer for one design has only priced one design. On the right house that is fine; on the wrong one it is an expensive way to find out there was a choice. I would rather price both and show you the difference. That is what the $399 solar and battery design visit is: your existing system tested, the roof, the board and the connection assessed, and a written design with the options priced against each other, credited in full off the install if you go ahead. If you just want an honest look first, the $99 site inspection gets you a same day written quote with the $99 credited back on the job.

Common questions