Understanding AC-Coupled Batteries

Understanding AC-Coupled Batteries


AC vs DC Coupled Battery Systems

DC-Coupled System

In a DC-coupled setup:

Solar panels generate DC electricity → this DC power directly charges the battery → then it is converted to AC by a hybrid inverter for use in the home or export to the grid.


AC-Coupled System

In an AC-coupled setup:

Solar panels generate DC electricity → a solar inverter converts this to AC → the AC electricity is used by the household and/or sent to a battery inverter, which re-converts AC to DC to charge the battery.




How to Know if Your AC-Coupled Battery Is Working

A simple way to check if your AC-coupled battery system is functioning correctly is to observe its behavior throughout the day:

  • In the morning and afternoon: the battery should be charging, as solar production is available.

  • At night: the battery should be discharging, providing power to the home when solar is no longer available.

If you see this pattern, charging during the day and discharging at night then your battery system is doing its job.



How Power Flow Monitoring Works

Accurate load calculation in a solar-plus-storage system depends on the inverter’s ability to monitor three key data points:

  1. Solar Production – the amount of power generated by the solar panels.

  2. Battery Power – positive when discharging, negative when charging.

  3. Grid Power – positive when importing power from the grid, negative when exporting.

By using these three values, the inverter can determine the actual load (i.e., how much power is being consumed by the home or site):

Load = Solar Power + Battery Power + Grid Power

Example 1:

  • Solar: 3000 W

  • Battery: -2000 W (charging)

  • Grid: 0 W

    → Load = 3000 - 2000 + 0 = 1000 W

Example 2:

  • Solar: 3000 W

  • Battery: 0 W (fully charged)

  • Grid: 2000 W (importing)

    → Load = 3000 + 0 + 2000 = 5000 W

Example 3:

  • Solar: 6000 W

  • Battery: -2000 W (charging)

  • Grid: -1000 W (exporting)

    → Load = 6000 - 2000 - 1000 = 3000 W



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