AC Coupling

A battery topology where the battery has its own inverter and connects to the household AC bus, alongside (rather than through) the solar inverter.

AC coupling is the simpler of the two battery integration topologies. The solar PV system stays unchanged with its own inverter, and the battery is a self-contained AC unit (battery + inverter in one box) connected at the consumer unit. Tesla Powerwall, GivEnergy AC, Sonnen and Enphase IQ are common AC-coupled choices.

Advantages: easy retrofit to existing solar (especially valuable for Cornwall's many legacy FiT systems), no impact on solar generation if the battery fails, and the FiT 50% deemed export is preserved. Disadvantage: there is a small efficiency loss (around 5%) on every round-trip through DC→AC→DC→AC.

For new installs without legacy FiT, DC coupling may be more efficient. For retrofit to a working system, AC coupling is almost always the right answer. See our battery storage page for system design.