Should your solar PV system be AC or DC coupled?
In an AC-coupled PV systems, the solar panels and Battery Energy Storage System (BESS) each have their own inverter. The solar panels produce DC power, which is converted to AC via a grid-tie inverter. The BESS stores and delivers DC power, so a separate battery inverter converts AC back to DC for storage, and vice versa when the BESS discharges energy to the load.
DC-coupled systems are generally more efficient due to fewer power conversions, but AC coupled systems are less expensive initially and offer greater flexibility for expanding the system. Also, as AC coupled systems supplement the grid energy that is dispatched to load, sizing the system is less complicated. However, with DC coupled systems, the power generally flows to the load via the Hybrid inverter and so sizing the system correctly is very important. This is also true for the Hybrid Battery Inverter in an AC-couped system where the “essential” or back-up power load must be within the capacity limits of the Hybrid/Battery inverter. Getting this wrong can be very costly.
AC coupled solar PV+BESS system
DC coupled solar PV+BESS system
How it works:
- DC coupled:
Solar panels generate DC power, which is directly fed to the battery storage system without any initial AC conversion.
- AC coupled:
Solar panels generate DC power, which is converted to AC by the grid-tie inverter before being sent to the battery storage system. This energy then needs to be converted to DC for storage and then converted back to AC to be discharged to load.
AC-coupled solar PV system
Advantages
✅ Flexibility — You can add storage to an existing solar PV system without much reconfiguration.
✅ Compatible with retrofits — If you already have grid-tied solar, adding batteries is easier.
✅ Works with various inverter brands — More mix-and-match options.
✅ Easier to split off-grid and on-grid functions (helpful for backup systems).
Disadvantages
❌ Double conversion losses — Power goes through more conversion steps (DC to AC to DC and back to AC).
❌ Slightly lower round-trip efficiency due to extra conversions.
❌ More complex wiring and potential for slightly higher installation costs.
DC-coupled solar PV system
Advantages
✅ Higher efficiency — Fewer power conversion steps, so better round-trip efficiency.
✅ Simplified system — A single inverter handles both solar and battery.
✅ Potentially lower cost for new installs (fewer components).
Disadvantages
❌ Less flexible — Harder to retrofit into an existing AC solar system.
❌ Inverter compatibility — System depends heavily on the hybrid inverter working well with the battery and panels.
❌ May require more detailed system planning upfront (less modular).
Summary Comparison Table
| Feature | AC-Coupled | DC-Coupled |
| Efficiency | Lower (more conversions) | Higher (fewer conversions) |
| Flexibility | Higher (good for retrofits) | Lower (best for new installs) |
| Installation | More wiring and parts | Simpler for new installs |
| Cost for retrofits | Lower (works with existing solar) | Higher (may require full system redo) |
| Inverter dependence | Independent solar + battery inverters | One hybrid inverter does all |
When to choose which one:
- For maximum system efficiency:
Choose a DC coupled system if maximizing energy production is your primary concern.
- For easy integration with existing systems:
Choose an AC coupled system if you want to easily connect your solar system to your existing electrical grid or if you think that you will need to expand the system later.
