In-depth Analysis: Grid-connected inverters – anti-backflow devices ≠ hybrid grid systems: Clarifying key misconceptions in the industry

First, let us clarify the basic definitions of these two core pieces of equipment to establish a professional framework of understanding. The core design logic of a conventional grid-connected inverter is ‘grid-connected power generation, with surplus electricity fed into the grid’. The equipment has no independent energy storage or operational priority and is primarily suited to distributed grid-connected photovoltaic systems. Its core function is to convert DC power from the photovoltaic system into AC power, prioritising supply to local loads, whilst any surplus electricity is fed directly into the public national grid. The grid serves as the system’s core foundation; should the grid power be cut off, the grid-connected inverter will simultaneously disconnect from the grid and shut down, and is unable to operate independently.

An anti-reverse-flow device, on the other hand, is a complementary monitoring and protection peripheral. Its core function is to monitor the direction of current flow and power data at the grid connection point in real time. Through data sampling and signal feedback, it prevents the photovoltaic system from feeding electricity back into the public grid. Put simply, its sole function is to prevent surplus electricity from being fed into the grid, enabling the grid-connected photovoltaic system to achieve ‘self-generation for self-consumption with zero surplus electricity fed into the grid’. It retains only the backup power supply function from the mains, thereby eliminating reverse power flow, metering disputes and grid safety hazards.

Diagram illustrating the differences between the two core types of grid-connected inverters: standard grid-connected inverters and anti-reverse-flow grid-connected inverters

Many users mistakenly believe that ‘a grid-connected inverter plus anti-backfeed protection equals a hybrid system’. The core misconception lies in the fact that this combination achieves the apparent functionality of ‘self-consumption of solar power, battery storage and grid supplementation’, which appears to combine both grid-connected and off-grid characteristics, leading to its subjective definition as a hybrid system.

However, the overlap in apparent functions does not equate to an identical technical architecture. A genuine hybrid PV system (the full technical term being ‘hybrid PV-storage system’) possesses a dedicated hardware architecture, dual-mode independent operation algorithms and bidirectional power dispatch logic; it is a distinct system category entirely separate from the ‘grid-connected + anti-backfeed’ configuration.

We have conducted an in-depth analysis of the fundamental differences between the two, examining four core dimensions: operational logic, power supply architecture, equipment characteristics and fault mechanisms.

▶ Firstly, the operational priorities and power dispatch logic are entirely different.

A grid-connected inverter system fitted with a back-feed prevention device still relies primarily on the public grid; its operational benchmarks and voltage/frequency parameters are entirely synchronised with the utility grid. Its operational mode is straightforward: surplus solar power is prioritised for self-consumption, whilst the utility grid supplements any shortfall; throughout, there is no autonomous dispatch via energy storage, nor any capability for off-grid independent operation. The anti-backfeed device merely cuts off the reverse power feed circuit; it does not alter the underlying logic of the grid-connected inverter’s operation. The equipment still does not support off-grid independent operation and lacks the ability to switch freely between modes characteristic of a hybrid system.

In contrast, a true hybrid system is an adaptive, intelligent system capable of both grid-connected and off-grid modes, with bidirectional autonomous dispatch capabilities. The system can intelligently switch between grid-connected operation and off-grid independent operation based on grid status, sunlight conditions and battery charge levels. When the grid is functioning normally, it can operate in grid-connected mode for self-consumption and feed electricity into the grid as required; in the event of a grid power cut or voltage abnormalities, it can automatically disconnect from the grid and switch to a pure off-grid energy storage power supply mode, operating independently to support the load and forming a self-sufficient power supply loop—a core function that the ‘grid-connected + anti-reverse flow’ solution completely lacks.

▶Secondly, there are fundamental differences in energy storage compatibility and power supply mechanisms.

Grid-connected systems fitted with anti-reverse-flow protection have extremely poor energy storage compatibility and lack active battery dispatch logic. This solution is unable to manage battery charging and discharging in depth; the batteries can only serve as auxiliary backup and cannot participate in system power regulation or load voltage stabilisation. Once the battery charge is depleted, the system must rely entirely on the mains supply, making it no different in essence from a standard grid-connected system. Furthermore, this system cannot prioritise power supply from the batteries, meaning it fails to maximise the utilisation of stored energy, resulting in an extremely low utilisation rate for the photovoltaic-storage system.

The core advantage of a standard hybrid grid system lies in the three-dimensional coordination of solar, storage and the grid. It incorporates a specialised BMS (Battery Management System) with coordinated algorithms and a PCS (Power Conversion System), enabling precise dispatch of power from the solar panels, batteries and the mains supply. During the day, electricity generated by the solar panels is prioritised to power loads and charge the batteries; at night, the batteries are prioritised for discharge to provide a safety net; when the battery is depleted, the mains grid provides top-up power; in the event of a grid fault, the system disconnects from the grid to protect itself. Power is intelligently allocated throughout the process, maximising the utilisation of renewable energy and reducing mains power losses—something that pseudo-hybrid grid solutions cannot achieve.

▶ Thirdly, the ability to operate off-grid is the key distinguishing factor and the most crucial difference.

A grid-connected inverter combined with an anti-backfeed device lacks the capability for off-grid operation; this is the key criterion for determining that it is not a hybrid grid system. According to State Grid’s safety regulations for grid-connected equipment, pure grid-connected inverters (regardless of whether they are fitted with anti-backfeed devices) are equipped with a grid undervoltage disconnection protection mechanism. Should the public grid experience a power cut, outage or voltage instability, the equipment will immediately lock and shut down, ceasing output entirely; it is unable to provide independent power to the load, resulting in complete system failure.

In contrast, genuine hybrid grid-connected inverters (integrated PV-storage units) are equipped with independent line-frequency voltage stabilisation modules and islanding protection bypass systems, providing full off-grid load-carrying capability. They operate in grid-connected mode when the grid is functioning normally, and automatically switch to islanding mode in the event of grid abnormalities or power cuts, operating independently of the grid by relying on power from the PV system and batteries. This enables efficiency gains through grid connection when power is available and ensures a continuous power supply via off-grid operation when it is not—which is the core value of hybrid grid-connected systems.

Video: A Comparison of the Operating Principles of Hybrid Grid-Connected Inverters and Anti-Reverse-Flow Grid-Connected Inverters

▶Fourthly, the official industry definition differs entirely from equipment certification standards.

In the national standards for the photovoltaic energy storage industry, equipment manufacturers’ parameter definitions, and project tendering standards, ‘grid-connected with anti-backflow’ has never been defined as a hybrid grid system. The industry clearly distinguishes between three types of systems: pure grid-connected systems, pure off-grid systems, and photovoltaic-storage hybrid grid systems; the hardware architecture, control programmes and certification requirements for these three are entirely independent of one another.

Hybrid grid-connected inverters are specialised, integrated devices that come factory-fitted with a full suite of functions, including grid-connected/off-grid dual-mode switching, bidirectional power dispatch, islanded operation and intelligent energy storage management; they constitute a distinct category of equipment. By contrast, anti-reverse-flow devices are merely external auxiliary protective components that merely alter the direction of power flow in a grid-connected system; they cannot change the underlying characteristics of the equipment and therefore constitute a functional modification rather than a system-level upgrade. Modified grid-connected equipment remains classified as a grid-connected system and does not constitute a hybrid grid system; this modification is commonly referred to by users as a ‘pseudo-hybrid grid’.

From the perspectives of practical performance and engineering implementation, this pseudo-hybrid grid solution still has significant shortcomings. Firstly, it is functionally limited and lacks the ability to maintain power supply during outages; the system shuts down immediately upon a mains power cut, failing to address emergency power requirements. Secondly, energy storage utilisation is low; it cannot prioritise battery power supply, thus failing to reduce electricity bills for mains power. Finally, it suffers from high failure rates and poor compatibility; retrofitted anti-reverse-flow devices often experience software incompatibility and signal delays with the original grid-connected inverters, which can easily lead to faults such as voltage fluctuations, erroneous protection shutdowns and equipment error messages.

Conversely, the reason many users endorse this solution lies solely in the fact that it resolves the issues associated with standard grid-connected systems—namely, ‘excess electricity being fed into the grid haphazardly, leading to disputes over electricity charges’—by enabling self-consumption of solar-generated electricity with zero reverse power flow, whilst providing a mains power backup that eliminates the need for frequent manual switching. However, the fact that certain functional aspects overlap does not equate to the systems belonging to the same product category; this is the industry’s greatest misconception.

Summary

The core characteristics of a hybrid grid system are dual-mode adaptive operation, the integration of photovoltaic, storage and the grid, the ability to operate both on-grid and off-grid, and bidirectional power dispatch; none of these can be omitted. In contrast, a grid-connected inverter fitted with an anti-backfeed device merely fulfils a single function: ‘grid connection without self-supply, mains backup, and self-consumption of solar power’. It lacks off-grid independent operation, intelligent energy storage dispatch, and dual-mode switching; consequently, it does not possess the core underlying attributes of a hybrid grid system and therefore absolutely cannot be termed a hybrid grid system, but is merely an improved version of an anti-backfeed grid-connected system.

When selecting a system, users must strictly distinguish between these concepts and avoid being misled by colloquial terms. They should carefully choose between a pure off-grid, true hybrid or anti-backfeed grid-connected solution based on their specific core requirements, such as power supply continuity during outages, energy storage management and independent power supply.