Differences between DC- and AC-coupled storage systems

Differences Between DC- and AC-Coupled Storage Systems

In recent years, photovoltaic (PV) technology has developed rapidly, and the installed capacity has increased quickly. However, the intermittent and uncontrollable nature of PV remains a challenge. Without an appropriate solution, directly feeding large amounts of PV energy into the grid can cause significant disturbances and affect the stability of power networks.

By integrating energy storage systems, the PV power generation can be smoothed and fed stably into the grid without compromising grid stability. Additionally, combining PV with storage significantly expands the potential applications of such systems.

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Differences Between DC‑ and AC‑Coupled Storage Systems 

 In recent years, photovoltaic (PV) technology has advanced rapidly and installed capacity has surged. Yet the intermittent, uncontrollable nature of PV remains a challenge. Without suitable mitigation, feeding large amounts of PV energy directly into the grid can cause serious disturbances and undermine grid stability. By integrating energy storage, PV output can be smoothed and injected stably—preserving grid reliability—and the combination of PV plus storage greatly broadens system applications.

A typical PV‑storage installation comprises solar modules, charge controllers, inverters, batteries and loads. Many technical approaches exist, but they all collect energy at a single point. The two principal topologies are DC coupling and AC coupling.

DC Coupling

With DC coupling, the direct current produced by the PV modules is routed through a charge controller into the battery. The grid can also charge the batteries via a bidirectional DC‑AC converter. The single point of energy concentration is on the DC (battery) side.

How DC Coupling Works

• The PV generator charges the battery via a Maximum Power Point Tracker (MPPT) controller.

• When loads demand power, the battery discharges, with current determined by the load.

• The system remains grid‑connected; if the battery is full and load is low, the PV generator may feed surplus into the grid.

• If load exceeds PV output, both grid and PV supply the loads, with the battery balancing the difference.

AC Coupling

In AC coupling, PV‑generated DC is first converted to AC by an inverter, then delivered directly to loads or exported to the grid. The grid can likewise replenish the batteries via a bidirectional DC‑AC converter. Here, the point of energy concentration sits on the AC side.

How AC Coupling Works

• The installation comprises two sub‑systems: a PV generation system and a separate battery storage system.

• The PV side consists of the PV array plus a grid‑tie inverter; the storage side consists of the battery plus a bidirectional inverter.

• Both can operate independently or together within a microgrid.

Comparing DC vs. AC Coupling

Cost

• DC coupling requires charge controllers, bidirectional inverters and transfer switches.

• AC coupling requires grid‑tie inverters, bidirectional inverters and distribution panels.

• Because controllers and switches typically cost less than grid‑tie inverters and distribution gear, DC coupling is often more economical.

Applicability

• DC coupling wires controller, battery and inverter in series, which constrains flexibility.

• AC coupling wires grid‑tie inverter, battery and bidirectional inverter in parallel, offering greater flexibility.

• For retrofitting existing PV systems, AC coupling is ideal—just add a battery and bidirectional inverter.

• For greenfield micro‑grids where PV, battery and inverter are sized to the load, DC coupling is preferable. However, very large systems (> 500 kW) are generally easier to manage via AC coupling.

Efficiency

• AC coupling shines under high daytime load: PV modules can directly power loads through the grid‑tie inverter, minimizing conversion steps.

• DC coupling excels under high nighttime load: PV energy is routed directly to the battery, reducing conversion losses.

Outlook – Intersolar Munich 2025

At Intersolar Munich 2025 we’ll see a host of new developments—especially in inverters and battery storage. As industry innovators, we’re proud to help drive these trends forward. Chinese manufacturers in particular are moving fast to showcase the latest technologies. Stay tuned for the exciting announcements this year’s exhibition will bring!