AC coupled battery

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

An AC coupled battery connects to the home’s AC wiring through its own battery inverter. The solar system keeps its inverter and carries on as before. The battery sits beside it and charges from whichever AC source is available: solar, or the grid if the settings allow.

The energy path explains the trade-off. Solar DC becomes AC at the solar inverter. To charge the battery it becomes DC again, then returns to AC on discharge. That is three conversions where DC coupled uses fewer, which is why whole-system round-trip efficiency is usually a bit lower.

In practice

AC coupling is the common answer for retrofits. The customer already has panels and a working inverter, perhaps a few years old, and wants a battery. Adding a self-contained battery with its own inverter avoids replacing equipment that still works. It also gives flexibility on location, since the battery can sit away from the solar inverter.

Under the Cheaper Home Batteries Program, a battery can be added to existing solar. The battery needs to be CEC-approved, VPP-capable and installed by an accredited installer, and the STC count comes from usable capacity, whichever way the system is coupled. See usable capacity.

For blackout protection, AC coupled systems need a backup power gateway and careful design so the solar inverter can run during an outage without overloading the battery.

Common confusion

AC coupled does not mean slower or worse. For many homes, the extra conversion loss is small compared with the saving of keeping the existing inverter.

It also does not change eligibility. The type of coupling is not a factor in the STC calculation, and the tier percentages apply in the same way. See battery tier factor.

Process detail is in battery STCs and the battery submission guide. The glossary has more terms.