AC and DC augmentation in BESS: the differences between the two approaches

AC augmentation

AC augmentation connects new batteries up to the AC bus of the BESS system, i.e. after the inverter. This means that any new batteries added to the BESS need to be installed alongside new inverters and control systems and leaves the rest of the system unchanged. AC augmentation is essentially the process of adding an independent battery system to the existing BESS. This approach enables incremental sizing and carries a low risk of technical complications.

AC augmentation is a simpler approach from a technical standpoint that doesn’t require extensive modifications to the existing BESS and is a lot less disruptive to the everyday operation of the BESS compared to DC augmentation. Even though it is simpler installation from a technical standpoint, it requires a lot of extra permitting and regulatory approval that can make the installation process slow and complicated from a regulatory standpoint.

It should be noted that these challenges are for grid-tied BESS only. BESS that are independent from the grid don’t need to undergo such lengthy regulatory processes, which makes off-grid BESS and islanded microgrids well-suited for AC augmentation. For grid-tied BESS, AC augmentation is used more for utility scale expansion and for long-term projects that have plans to be scalable over time.