AC-coupled battery

Written and checked by the Energy Merchants desk · Reviewed 3 October 2026

An AC-coupled battery has its own inverter and connects to the AC wiring of the property, next to the solar system. The solar panels keep their own inverter and the battery works independently of them.

How the energy flows

Solar produces DC, the solar inverter converts it to AC for the house, and any spare AC is converted back to DC to charge the battery. When the battery discharges, its inverter converts it to AC again. That is three conversions in the worst case, and each costs a little energy. Round-trip efficiency is therefore somewhat lower than for a DC-coupled design.

In practice

AC coupling is the usual choice when adding a battery to an existing solar system. The existing inverter stays in place, which keeps cost and disruption down. The Cheaper Home Batteries Program works with new or existing solar, so a large share of retrofit jobs are AC-coupled. The battery still needs to meet the program’s conditions: CEC-approved, VPP-capable, installed by an accredited installer, one per property. See battery STCs.

The STC quantity depends on usable capacity and the factor, not on the coupling type. See usable capacity and STC factor.

Worked example

A home has a 6.6 kW solar system installed in 2021 with a string inverter. The customer adds a 10 kWh usable AC-coupled battery in 2026. The battery brings its own inverter and wires to the switchboard. It creates 10 x 6.8 = 68 STCs at the time of writing, with no change to the solar system.

Common confusion

AC coupling is not the same as being “AC battery” in the sense of storing AC. All batteries store DC. The coupling describes where the battery connects. It also does not mean the battery cannot back up the home. Backup depends on the model and the wiring, not the coupling.

Compare DC-coupled, read the battery submission guide and browse the glossary.