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A new analysis published on 2026-05-26 by Energy Storage News examines the technical and economic trade-offs between AC and DC coupling for co-located solar and battery energy storage system (BESS) projects.
Co-locating solar photovoltaic (PV) installations with BESS technology allows the two assets to share a single grid connection. This configuration can reduce curtailment in renewable energy installations by storing energy generated at peak times for later use, rather than wasting it. For the grid, co-location supports load shifting to reduce strain during peak demand periods. For asset owners, sharing grid infrastructure such as transformers and cabling can lower both capital and operational expenditures, while storing and discharging energy when prices are high can increase revenue.
AC coupling remains the most common approach for co-location projects. In this configuration, the BESS connects to the AC side of the solar power system. Both the solar array and the BESS use their own inverters to convert DC electricity to AC before any power reaches the grid. Solar PV generates DC power, which is converted to AC by the solar inverter. This AC power either goes directly to the grid or passes through the BESS inverter to be converted back to DC for storage. When the stored energy is needed, the BESS inverter, or power conversion system (PCS), converts it back to AC for on-site use or export to the grid.
The dual-inverter setup makes installation simpler and offers greater system flexibility than DC coupling. However, AC coupling tends to cost more because multiple inverters must be purchased and installed. Additionally, because energy designated for storage undergoes multiple conversions (DC-AC to AC-DC back to DC-AC), AC coupling results in a lower round-trip efficiency compared to DC coupling, as each inversion process incurs energy losses.
The analysis notes that AC coupling is best suited for retrofit projects. It is also the preferred option in specific scenarios where the advantages outweigh those of DC coupling.
DC coupling integrates the BESS into the DC side of the system, sharing a common DC bus with the solar array. Because both assets connect on the DC side before the inverter, only one inverter—typically a multi-modal unit—is required. Combined DC power from the BESS and solar panels passes through this inverter, where it is converted to AC for local loads or the grid.
DC coupling is cheaper than AC coupling due to reduced hardware requirements, but metering is more difficult because energy is shared through the inverter rather than separately metered as in an AC-coupled system. Efficiency can reach up to 98% because there is only a single power conversion process; the battery can be charged directly with harvested DC electricity without repeated conversions. Solar energy can be stored directly from the panels, and DC-coupled systems can also charge from the grid during periods of low solar generation. Unlike AC coupling, no export-limiting hardware is needed, as the inverter clips any energy above the grid export capacity, making it physically impossible to exceed that limit.
DC coupling is preferred for new solar-BESS co-location projects on greenfield sites, for projects prioritizing round-trip efficiency and lower costs, and for off-grid and microgrid applications where efficiency is critical. For large-scale energy storage systems, DC coupling reduces energy losses from repeated AC-DC conversions over time, improving return on investment. In commercial and industrial settings such as warehouses, factories, and large office complexes, the higher efficiency helps ensure that more energy harvested by solar panels reaches the loads.
The analysis describes two approaches to DC coupling. In older systems, a bidirectional DC-DC converter with a maximum power point tracking (MPPT) charge controller is installed between the solar array and the BESS to match voltage levels. This method is commonly used in commercial, industrial, and utility-scale installations. In these systems, solar panels connect directly to the shared DC bus, while the BESS connects via the DC-DC converter. A central or string inverter at the end of the bus connects to the AC side.
Newer systems use integrated hybrid inverters with built-in MPPT charge controllers. This is now the most common approach, as the hybrid inverter handles both solar and BESS inputs through separate input ports. Energy from the solar panels enters via MPPT inputs, where the inverter adjusts voltage to match the battery voltage. When energy is needed for loads or the grid, power from the battery, solar panels, or both is transferred to the inverter and converted to AC.
The choice between AC and DC coupling depends entirely on the type of installation, as each approach has distinct advantages and disadvantages. For retrofit projects, AC coupling is the recommended option. For new installations, the benefits of DC coupling may outweigh its drawbacks. The analysis concludes that understanding the pros and cons of each approach helps determine which method best suits a project’s budget, capital expenditure, available space, operational needs, and efficiency requirements.
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