With the rapid development of solar energy storage systems, inverters, as core components connecting photovoltaic (PV) panels, energy storage batteries, and the power grid/loads, have evolved into multiple types to adapt to different application scenarios. Among them, AC couple inverters, battery inverters, and hybrid inverters are widely used but often confused due to overlapping functions in energy conversion. Essentially, these three types of inverters differ significantly in energy coupling paths, functional integration, system architecture, and applicable scenarios. This article will systematically elaborate on their core differences to help readers better understand and select the appropriate inverter type.
Before delving into the differences, it is crucial to clarify the basic definitions and core functional orientations of each inverter, which lay the foundation for understanding their operational mechanisms.
An AC couple inverter, also known as an AC-coupled energy storage inverter, is a bidirectional power conversion device that realizes energy interaction between the AC power grid (or AC loads) and energy storage batteries. Its core feature is that energy coupling occurs on the AC side—both charging the battery and discharging from the battery need to go through AC/DC conversion. Notably, it does not have a Maximum Power Point Tracking (MPPT) module and cannot directly connect to PV panels; instead, it relies on an external PV inverter to convert PV energy into AC power before utilizing it for battery charging or direct load supply.
A battery inverter, narrowly defined, refers to a bidirectional converter specifically responsible for the charging and discharging management of energy storage batteries. Its main function is to convert the DC power stored in the battery into AC power that can be used by the grid or loads (discharging process), and convert the AC power from the grid or PV system into DC power to charge the battery (charging process). In most cases, the battery inverter mentioned in practical applications is an AC-coupled type, which is similar to the AC couple inverter in terms of coupling path but has a more focused positioning on battery management. It also lacks an MPPT module and needs to be matched with an external PV inverter to form a complete PV-storage system.
A hybrid inverter is an integrated power conversion device that combines the functions of a PV inverter, a battery inverter, and a battery management system (BMS). Its core advantage lies in integrated functional integration—equipped with an MPPT module that can directly connect to PV panels to maximize PV power generation, and also has a battery interface to realize direct DC-coupled energy interaction with energy storage batteries. In addition, it can flexibly switch between grid-connected and off-grid modes, and independently complete the conversion, distribution, and management of PV energy, battery energy, and grid energy, forming an integrated PV-storage system with a high degree of integration.
The differences between the three types of inverters are concentrated in energy coupling paths, functional integration, system architecture, conversion efficiency, and applicable scenarios. The following table systematically sorts out their differences from multiple dimensions:
| Comparison Dimension | AC Couple Inverter | Battery Inverter (Narrowly Defined) | Hybrid Inverter |
|---|---|---|---|
| Energy Coupling Path | AC-side coupling: PV→DC→AC (by external PV inverter) →AC→DC (charging) →DC→AC (discharging) | AC-side coupling: Grid/PV AC power→DC (charging) →DC→AC (discharging); same as AC couple inverter | DC-side coupling: PV→DC→DC (MPPT & charging) →Battery→DC→AC (discharging); no redundant AC/DC conversion |
| Core Functional Integration | Bidirectional AC/DC conversion; no MPPT, no BMS; relies on external devices | Bidirectional AC/DC conversion; basic battery charging/discharging management; no MPPT; needs external PV inverter | Integrates MPPT, bidirectional DC/AC conversion, BMS, and grid/off-grid switching; all-in-one control |
| System Architecture | Parallel with external PV inverter on AC bus; modular design; independent control | Parallel with PV inverter/grid on AC bus; simple structure; independent battery management | PV panels and batteries share DC bus; high integration; centralized control; fewer peripheral devices |
| Energy Conversion Efficiency | Low (90%-92%); redundant AC/DC conversion leads to energy loss | Low (90%-92%); same as AC couple inverter due to AC-side coupling | High (94%-97%); DC-coupled path reduces conversion links and energy loss |
| Direct PV Connection | No; relies on external PV inverter | No; needs external PV inverter for PV energy utilization | Yes; built-in MPPT supports direct PV panel connection |
| Off-Grid Capability | Weak; relies on grid or external PV inverter to support voltage/frequency; most lack grid-forming capability | Weak; same as AC couple inverter; poor off-grid stability | Strong; built-in grid-forming capability; can independently form a microgrid for off-grid power supply |
| Expansion Flexibility | High; can be mixed with PV inverters of different brands; easy to expand energy storage capacity | High; modular expansion; compatible with most PV systems | Low; expansion is limited by inverter power and battery voltage range; needs matching components |
The selection of the three types of inverters is closely related to the actual application scenario, especially whether there is an existing PV system, efficiency requirements, and off-grid needs. The following are their typical application scenarios:
It is mainly suitable for energy storage retrofitting of existing PV systems. For users who already have a grid-connected PV system and want to add energy storage functions later, the AC couple inverter can be directly connected in parallel to the existing AC bus without modifying the original PV inverter or wiring. This retrofitting method has the advantages of short construction period, good compatibility, and low transformation cost. In addition, it is also suitable for scenarios that require flexible expansion of energy storage capacity, such as industrial and commercial PV plants that need to adjust energy storage scale according to peak-valley electricity price changes.
It is applicable to pure energy storage systems or simple PV-storage retrofitting. For scenarios without PV power generation (such as grid peak shaving and valley filling, off-grid emergency power supply), the battery inverter can realize the interaction between the battery and the grid independently. For existing PV systems with simple structures, the battery inverter can also be used for low-cost energy storage retrofitting, but it should be noted that it needs to be matched with the original PV inverter to ensure stable operation. In addition, it is also widely used in small-scale energy storage projects with low efficiency requirements and limited budgets.
It is the first choice for newly-built integrated PV-storage systems. For users who plan to build a PV-storage system from scratch, the hybrid inverter can reduce the number of equipment (no need for an additional PV inverter), simplify the system structure, and lower installation and operation and maintenance costs. It is especially suitable for scenarios with high off-grid requirements, such as rural areas with unstable grid power supply, remote mountainous areas, and outdoor operation sites that need independent power supply. In addition, it is also applicable to residential PV-storage systems that pursue high energy utilization efficiency, as its high conversion efficiency can maximize the utilization of PV energy and reduce electricity costs.
To sum up, AC couple inverters and battery inverters (narrowly defined) are essentially AC-coupled energy storage conversion devices, with the characteristics of simple structure, good compatibility, and low retrofitting cost, but they have the disadvantages of low efficiency and weak off-grid capability; hybrid inverters are integrated DC-coupled devices, with high efficiency, strong off-grid capability, and high integration, but they have limitations in expansion flexibility and higher initial investment cost.For selection, the following suggestions can be referred to:
With the continuous advancement of inverter technology, the boundaries between some types of inverters are gradually blurred (for example, some high-end battery inverters also integrate partial MPPT functions). When selecting, it is necessary to comprehensively consider the actual needs, product parameters, and application scenarios to ensure the optimal performance of the entire energy storage system.