This is mostly an installer-level technical decision, but understanding it helps you follow the conversation and ask better questions.
DC-coupled: battery connects before the inverter
In a DC-coupled system, the battery connects directly to the DC side of the system — solar panels charge the battery in DC, and a single inverter (a hybrid inverter) converts to AC only once, whether powering the home or exporting to the grid. This tends to be more efficient (fewer conversion steps) and is common in new installations designed with both solar and battery from the start.
AC-coupled: battery has its own inverter, connects after
In an AC-coupled system, the battery has its own separate inverter and connects to the home's AC circuit alongside the existing solar inverter — power gets converted DC-to-AC by the solar inverter, then AC-to-DC to charge the battery, then DC-to-AC again to use it, more conversion steps than DC-coupled. This is the more common approach for retrofitting a battery onto an existing grid-tied solar system, since it doesn't require replacing the existing solar inverter.
Efficiency difference is real but usually modest
The extra conversion steps in an AC-coupled system introduce some additional loss, similar in principle to the losses discussed in our inverter loss calculator — typically a few percentage points, not enormous, but a real factor in the efficiency comparison.
Which one you get often isn't really your choice
For a retrofit onto existing solar, AC-coupled is usually the practical (and sometimes only reasonable) option unless you're also replacing the existing inverter. For a new combined installation, DC-coupled with a hybrid inverter is increasingly the more common design choice from the outset.
Frequently asked questions
Is DC-coupled always more efficient than AC-coupled?
Generally yes on paper due to fewer conversion steps, though the real-world difference is often modest — a few percentage points — and shouldn't be the sole factor in choosing between a new combined system and a retrofit approach.
Can I retrofit a DC-coupled battery onto my existing solar system?
It's possible in some cases but often requires replacing the existing solar inverter with a hybrid inverter capable of DC coupling, which adds cost — AC-coupled is more commonly the practical retrofit path for existing systems.