AC vs DC coupled batteries: adding a battery to your Melbourne solar

AC vs DC coupling in one diagram

Solar panels and batteries both work in direct current (DC); your home and the grid run on alternating current (AC). “Coupling” is where the battery joins the system: on the DC side, through the same inverter as the panels, or on the AC side, through an inverter of its own.

Battery inverter or hybrid inverter?

Every battery needs an inverter; the question is which one. A battery inverter handles only the battery: it charges it from spare AC power at the switchboard and turns the stored energy back into AC for the home. Adding one beside your solar inverter is AC coupling. A hybrid inverter is, in Solar Victoria’s words, “designed to work with batteries and the grid”: it runs the panels and the battery together, and the guide describes it as an inverter “which includes a charge controller to allow connection of a DC-coupled battery”.

All-in-one batteries have the inverter in the same box and are “connected to your existing house switchboard, separately from the solar panels and solar inverter” (Solar Victoria’s Solar Battery Buyers Guide, section 4). Battery-only modules connect to a compatible inverter from the maker’s list, usually a hybrid.

Compare home batteries

Can you add a battery to the solar you already have?

Usually, yes. When a battery is added to existing solar, Solar Victoria notes that the inverter “often needs upgrading to a ‘hybrid’ inverter”, and that “The existing solar inverter can either be replaced or a second inverter added that is dedicated to the battery.” Which route suits your home depends on the inverter on your wall now:

1. Find the model. It is on the label on the side of the inverter and in its monitoring app. Read it only; don’t open covers or switch isolators.
2. Already a hybrid? If its maker lists a battery it takes, that battery can connect to it (DC coupled). Check that the battery is still sold and on the approved list.
3. A solar-only string inverter? Keep it and add a battery with its own inverter (AC coupled), or replace it with a hybrid and a compatible battery.
4. Microinverters under each panel? Solar Victoria says you will need a battery with its own dedicated inverter (AC coupling).

Microinverters vs string inverters

Why now? Victoria’s premium feed-in tariff scheme ended on 1 November 2024, so homes that had it now earn only their retailer’s feed-in tariff for spare solar, which can’t go below 0 cents per kWh. A battery keeps that solar for the evening instead.

How a battery install works

Why there is no minimum feed-in tariff

What does a ‘battery-ready’ inverter mean?

A battery-ready inverter is a hybrid that can take a battery now or later, but only the batteries its maker names. That list is the test, not the word on the brochure. Solar Victoria also warns that “any ‘hybrid’ inverter you install now could be obsolete by the time you purchase and install the battery”, because battery technology moves quickly, and adds: “Another approach is to initially install a relatively cheap solar inverter, and then replace it with a hybrid inverter later on when you want to add a battery.”

So a solar-only string inverter such as the Fronius Primo is not battery-ready: a battery needs its own inverter beside it. A hybrid is ready only for the batteries on its maker’s list. If your hybrid’s matching battery is no longer sold or approved for the rebate, AC coupling or a new hybrid is the way in. For the rebate, the hybrid itself must also be on the approved inverter list, now or when your solar was commissioned (see the rebate rules below).

Hybrid, string and microinverters

Keep your inverter and add an AC battery, or swap to a hybrid?

Both work. The choice comes down to the age of your inverter, whether you want more panels and how much inverter capacity your connection has left.

What the extra inverter costs

In that index, connecting a battery to existing solar added about $500 to $1,500. It has no figure for replacing a working solar inverter with a hybrid, so compare written quotes for both.

Upgrading an older solar system

Size the battery to your evening use

Efficiency, backup and oversizing differences

Efficiency

Every conversion between DC and AC loses a little energy, and AC coupling adds two for the solar it stores (see the diagram). Solar the home uses straight away is converted once either way.

Charging from the grid

Some homes charge the battery from the grid at off-peak rates when the panels make less, in winter for instance.Solar Victoria’s Solar Battery Buyers Guide says: “Typically, only AC-coupled systems can charge from the grid, although DC-coupled systems can be set-up to charge from the grid.” Whether that pays depends on your tariff.

Backup in a blackout

Solar Victoria says “Grid-connected solar PV systems, with or without a battery, are designed to switch off during a power outage”, and that “the ability to provide energy when the grid is down depends not just on the battery, but also the rest of the system design and which inverter is used.” On an AC coupled system, ask whether your existing solar can keep charging the battery during an outage, and which circuits the battery inverter can back up.

How battery backup works

Oversizing and inverter limits

Without a battery, the SAA Technical Requirements (version 1.9, February 2026) require the inverter to be at least 75% of the panels’ peak power; with a battery system connected, the panels can go further, within the inverter maker’s limit. On a hybrid the battery sits on the same inverter as the panels, so its limit (the “Panels it can run” column in the battery-ready table) decides how many panels you can add. On an AC coupled system the panels stay on the old inverter and its limit.

With the networks’ 10 kW per phase pre-approval, a single phase home with a 5 kW solar inverter has 5 kW left for a battery inverter; a hybrid uses one inverter for both.

Single or three phase: the limits

Rebate rules when adding a battery to existing solar

The federal Cheaper Home Batteries Program applies to a battery added to existing solar, AC or DC coupled. The Clean Energy Regulator works out the certificates from the battery’s usable capacity and install date only, so the same size gets the same rebate either way. The conditions:

• Installed by a Solar Accreditation Australia (SAA) accredited installer with battery endorsement.
• A new battery on the Clean Energy Council approved battery list.
• One battery claim per property.
• The battery system, including its inverter, must be able to join a virtual power plant (VPP); joining one is optional.
• New: made within 12 months of installation, and installed with new or existing solar of no more than 1 MW.

Which inverter has to qualify

On solar you already have, the Clean Energy Regulator says “The inverter the battery is connected to must be capable of participating in a VPP”, and “Other inverters on site, such as existing solar PV inverters, are not required to be VPP-capable.” With AC coupling, that is the battery inverter; the solar inverter you keep doesn’t have to qualify. A hybrid you already have must either “be currently listed on the CEC’s approved inverter list” or “have been listed at the time the solar PV system was commissioned”. “If the inverter doesn’t meet these requirements, it needs to be replaced.”

For example, a 10 kWh battery installed in May–December 2026 creates 68 certificates (STCs), worth up to about $2,600. Dollar figures use $38 per STC, the top of the $33–$38 the Clean Energy Regulator says agents usually pay, so treat them as a ceiling.

Who qualifies for the rebate

Which of our batteries are AC or DC coupled?

We fit Sungrow SBR and Alpha ESS SMILE-G3 batteries. How each one connects, from the makers’ documents:

The rebate needs the battery on the approved list, so check the listing date on your quote.

The batteries we install

AC and DC coupled batteries: your questions