When a solar panel produces electricity, it’s direct current (DC). Your home runs on alternating current (AC). An inverter converts between the two. Where a battery sits in that chain determines whether a system is AC-coupled or DC-coupled.
In a DC-coupled system, panels feed directly into a hybrid inverter that handles both the solar conversion and battery charging in one unit. Power only converts from DC to AC once, on the way out to your home. It’s efficient and clean, but requires that everything — panels, battery, inverter — be designed to work together. Most new solar-plus-storage installations use DC-coupled architecture when starting fresh.
In an AC-coupled system, the solar panels have their own inverter (converting DC to AC), and the battery has a separate inverter that converts that AC back to DC for storage, then back to AC when discharging. The extra conversion step loses a small amount of energy, typically 3–5%. The trade-off is flexibility: you can add an AC-coupled battery to any existing solar system regardless of what inverter is already installed.
When you’re getting quotes
If you’re buying solar and storage together as a new system, ask whether the proposal is DC-coupled and why. If you already have solar and are adding a battery, expect AC-coupling and confirm the battery inverter is compatible with your home’s electrical setup. Also ask about backup behavior during a grid outage — AC-coupled systems behave differently from DC-coupled ones when the grid goes down, particularly in how quickly they can switch to island mode.
Common questions
- What is the difference between AC-coupled and DC-coupled battery storage?
- In a DC-coupled system, solar panels, battery, and inverter are connected on the DC side — power flows from panels to battery to inverter in one path. In an AC-coupled system, the solar has its own inverter, and the battery has a separate inverter. They're connected on the AC side of the circuit. DC-coupled is slightly more efficient (fewer conversion steps). AC-coupled is more flexible and works with any existing solar installation.
- Which is better for adding a battery to an existing solar system in NC?
- AC-coupled is almost always the answer when you're adding storage to an existing system. Your solar inverter stays in place; the battery system adds its own inverter alongside it. Enphase IQ batteries are the most common example in NC — they pair with any brand of existing solar, not just Enphase panels. Replacing a functioning solar inverter just to switch to DC-coupled storage rarely makes financial sense.
- Does Duke Energy's PowerPair program specify AC or DC coupling?
- No. The PowerPair program cares about equipment eligibility and Trade Ally installation, not how the battery is coupled internally. Both AC-coupled and DC-coupled systems can qualify. What matters for PowerPair is that the solar and battery are installed together as a new system by a Duke Energy Trade Ally, and that the equipment meets program specifications.