What is Coupling?
"Coupling" is a concept widely used in fields such as electronics, power engineering, software engineering, and physics. It refers to the interaction or connection between two or more systems, devices, or components.
In the photovoltaic (PV) energy storage industry, coupling primarily refers to the way solar panels, energy storage batteries, and inverters are connected.
How Does DC Coupling Work?
In a DC-coupled system, solar panels and energy storage batteries are directly connected to a hybrid inverter. The direct current (DC) generated by the solar panels is stored directly in the battery via the Maximum Power Point Tracking (MPPT) controller without conversion.
Additionally, alternating current (AC) from the grid is converted into DC by the hybrid inverter before being stored in the battery. In a DC-coupled system, energy is aggregated at the battery (DC) side.
How Does AC Coupling Work?
In an AC-coupled system, there are two inverters:
· The solar inverter converts DC power generated by the solar panels into AC power to supply household loads (DC-AC).
· Any excess energy is converted back into DC by the storage inverter and stored in the battery (AC-DC).
When the solar panels are not working, the storage inverter converts stored battery power back into AC to supply household loads (DC-AC). In this system, solar panels and energy storage batteries are connected via alternating current (AC).
Key Differences Between DC and AC Coupling
The distinction between DC and AC coupling depends on the type of power used to charge the battery:
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If the battery is charged directly with DC, it is a DC-coupled system.
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If the power is converted from AC to DC before charging the batteries, it is an AC-coupled system.
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DC Coupling |
AC Coupling |
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System Efficiency |
Higher (only one DC-AC conversion, minimizing energy loss) |
Lower (multiple DC-AC conversions result in energy loss) |
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Application Scenarios |
Ideal for new PV + storage systems, optimized for self-consumption |
Best for upgrading existing PV systems with storage, with minimal system modifications; suitable for high daytime energy demand |
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Backup Power During Grid Outages |
Yes (strong off-grid capability) |
Depends on storage inverter configuration (e.g., Hinen AC5S' Grid Forming technology ensures continued system operation during outages, maintaining stable power supply) |
|
System Scalability |
Limited by hybrid inverter capacity, making ultra-high-power applications harder to expand |
Highly scalable: independent solar and storage inverters allow separate expansion of PV or storage capacity |
|
Battery Compatibility |
Different battery technologies require specific DC voltage levels, which may affect system design and compatibility |
More compatible: batteries connect via AC, making it easier to integrate different battery types |
Which One Should You Choose: AC or DC Coupling?
Based on the comparison above, you may now have a better understanding of the advantages and disadvantages of AC and DC coupling.
If you already have a PV system and want to upgrade it with energy storage, AC coupling is the best choice. It simplifies the installation and upgrade process while keeping investment costs low.
If you are building a new PV + storage system from scratch, DC coupling is the optimal solution. Although the initial investment is higher, the system’s higher energy efficiency translates into significant cost savings over its full lifecycle.
Additionally, it is recommended to check with local distributors for available subsidies or incentives, as some regions may favor AC or DC-coupled systems.
Hinen Solutions
Hinen offers a range of high-efficiency and intelligent AC- and DC-coupled solar energy storage solutions for households worldwide.
· Hinen A Series AC5S (5kW Single-phase AC-coupled All-in-one RESS): A dedicated AC-coupled energy storage system designed for upgrading existing PV installations. It features an integrated design, multiple safety protections, and advanced energy management. Its Grid Forming technology enables solar inverters to keep running during power outages, ensuring stable electricity supply. With AC5S, upgrading from a PV system to a PV + storage system becomes effortless, enhancing energy management and reducing electricity costs.
· Hinen A Series H15S (15kW Single-phase All-in-one RESS): With a conversion efficiency of up to 98%, it ensures optimal energy utilization and cost savings. During grid outages, the system switches over in less than 10ms, providing seamless power continuity for homes. Its 230V/63A off-grid output supports a maximum 15kW household load, delivering reliable and stable energy for uninterrupted living.
