Inverters & Charge Controllers

AC Coupling

AC coupling is a system architecture where the solar panels and battery storage each have their own separate inverter, and they interact through the AC (alternating current) side of the system rather than sharing a DC bus. The solar inverter converts panel DC to AC, while a battery inverter converts battery DC to AC and vice versa.

In an AC-coupled setup, the solar inverter feeds AC power into the home's electrical panel. The battery inverter also connects to the same panel, charging the battery from excess AC solar production and discharging AC power when needed. The solar and battery systems are independent — they do not share DC wiring, charge controllers, or DC-to-DC converters.

AC coupling's primary advantage is flexibility. It allows you to add battery storage to an existing grid-tie solar system without replacing the original inverter. Install a separate battery inverter (like an Enphase IQ Battery, Tesla Powerwall, or Victron MultiPlus), connect it to the electrical panel, and the two systems coordinate through frequency and voltage signaling on the AC bus.

The trade-off is efficiency. When solar charges the battery in an AC-coupled system, the energy undergoes two conversions: DC→AC (solar inverter) then AC→DC (battery charger). Each conversion incurs 3-5% losses. In a DC-coupled system with a hybrid inverter, solar goes directly to the battery as DC with only one conversion step, making DC coupling roughly 5-10% more efficient for battery charging.

AC coupling is the preferred approach for retrofitting batteries onto existing solar installations, for systems using microinverters (which inherently produce AC at the panel level), and for commercial projects where solar and storage procurement happens at different times. New installations without legacy equipment generally benefit more from DC coupling through a hybrid inverter.

Frequently Asked Questions

Is AC coupling or DC coupling better?

DC coupling through a hybrid inverter is 5-10% more efficient for battery charging because it eliminates one conversion step. AC coupling is better for retrofitting batteries onto existing systems and for microinverter setups. For new installations with battery storage planned from the start, DC coupling is typically the better engineering choice.

Can I AC-couple a battery with my existing microinverter system?

Yes. This is one of AC coupling's biggest strengths. Add a battery inverter (Enphase IQ Battery is designed for this) to your electrical panel, and it charges from your microinverters' AC output. You keep your existing solar equipment intact while gaining battery backup capability.