The following are the core differences between grid-tied inverters, off-grid inverters, and hybrid inverters, compared through functionality, application scenarios, and technical characteristics:
Application Scenarios:
Areas with stable grids that allow "net metering" (selling electricity back to the grid). Residential or commercial photovoltaic systems aimed at reducing electricity bills or earning revenue from electricity sales.
Advantages:
Simple structure and low cost. Efficient utilization of photovoltaic power generation, reducing reliance on the grid.
Limitations:
Cannot supply power during grid outages (no backup power function). Cannot store excess electricity and relies on the grid to balance supply and demand.
Application Scenarios:
Remote areas without grid coverage, such as mountains and islands. Scenarios requiring complete energy independence, such as emergency power supplies or mobile devices.
Advantages:
Operates completely off-grid, making it suitable for areas with unstable or no grid power. Provides continuous power supply capability (dependent on battery capacity).
Limitations:
High system cost due to the need for battery configuration. Limited battery capacity, requiring careful design to avoid power shortages.
Application Scenarios:
Homes or businesses that need backup power, such as areas with frequent power outages. Those looking to optimize electricity bills by utilizing peak and off-peak electricity price differences for charging and discharging. Microgrid systems or scenarios gradually transitioning to renewable energy.
Advantages:
High flexibility, as it is compatible with both grid-tied and off-grid needs. Economical: reduces electricity bills through energy storage and increases energy self-sufficiency. Reliability: seamlessly switches to battery power during grid outages.
Limitations:
Higher initial cost due to the need for battery and intelligent management system configuration. High technical complexity, requiring professional installation and maintenance.
In distributed photovoltaic power generation systems, terms such as grid-connected, off-grid, grid-connected with energy storage, and microgrid are frequently encountered. What do they each signify? Essentially, they represent several types of power generation systems related to distributed photovoltaic power. This article introduces the main characteristics of grid-connected power generation systems, off-grid power generation systems, and microgrids. It also provides a comparative table in terms of their connection to the grid, the need for energy storage devices, application scenarios, etc., to give you a clear picture.
A grid-connected photovoltaic system is directly connected to the public grid. The core components of this system include photovoltaic modules, grid-connected inverters, bidirectional meters, and the grid itself. The grid-connected inverter converts the direct current generated by the photovoltaic modules into alternating current, which is then used to power local loads. Any excess electricity is sold back to the grid through the bidirectional meter. 
Grid-connected power generation systems rely on the external grid and operate under the "self-consumption with surplus fed into the grid" or "full feed-in" modes. In the event of a power outage, the system does not operate to prevent the risk of electricity being fed back into the grid.
An off-grid power generation system operates independently of the grid and is not connected to it. It consists of photovoltaic modules, off-grid inverters, batteries, and loads. This system is entirely independent and does not rely on grid power, making it suitable for remote areas without grid coverage or regions with frequent power outages. Off-grid systems must be equipped with energy storage devices, typically batteries, to provide power during the night or when there is no sunlight. 
Off-grid power generation systems do not depend on the grid and operate under the "use while storing" or "store first, then use" modes, not affected by power outages. This system offers superior flexibility and mobility, requiring energy storage devices like batteries to store electricity generated during the day for use at night or during periods without sunlight.
Grid tie and off grid power generation systems are widely used in places with frequent power outages, where self-consumption of photovoltaic power cannot feed surplus into the grid, where the self-consumption electricity price is much higher than the feed-in tariff, or where peak electricity prices are much higher than off-peak prices.
The grid tie and off grid power generation system consists of photovoltaic modules, a solar inverter with grid and off-grid capabilities, batteries, and loads. The photovoltaic array converts solar energy into electricity when there is sunlight, supplying power to the loads through the solar inverter while charging the batteries. When there is no sunlight, the batteries supply power to the solar inverter, which then powers the AC loads.
Compared to grid-connected power generation systems, this system adds a charge-discharge controller and batteries, allowing the photovoltaic system to continue operating during grid outages, with the inverter switching to off-grid mode to power the loads.
A microgrid is a distribution network composed of distributed power sources (such as photovoltaic and wind power), loads, energy storage systems, and control devices. Compared to the integrated generation, transmission, distribution, and consumption over a wide area of the main grid, the microgrid primarily achieves local consumption of distributed renewable energy and energy exchange with the main grid. A microgrid can operate as an independent grid or be connected to the main grid for power exchange. Microgrid systems are known for their flexibility and efficiency, enabling the large-scale integration of distributed power sources and renewable energy. In a microgrid, the energy management system (EMS) enables coordinated control between the main grid, distributed power sources, and energy storage systems, thereby smoothing the fluctuations of distributed energy.
Off-grid and grid-tied home photovoltaic (PV) power generation systems mainly differ in the following aspects:
Grid-tied: Grid-tied systems are connected to the public grid. In addition to PV modules, an energy storage system, and an inverter, they also include grid-tied inverters, meters, and other equipment. The DC electricity generated by the PV modules is converted into AC electricity by the inverter, with part of it used for household appliances and the excess fed into the grid through the grid-tied inverter. When the PV system's generation is insufficient, the household can draw power from the grid, enabling bidirectional power flow.
For example, during prolonged periods of overcast or rainy weather, an off-grid system may experience a power outage due to depleted batteries until the weather improves and the PV modules resume generating electricity to recharge the batteries.
Grid-tied: Since it is connected to the grid, when the PV system's generation is insufficient (e.g., at night or during low-light conditions), the household can draw power from the grid, ensuring a stable power supply with little to no risk of interruptions.
For example, even when the home PV system stops generating electricity at night, household appliances can still operate normally as the power is supplied by the grid.
For instance, to meet a household's electricity needs for 3-5 days, a large-capacity battery system may need to be installed, which adds to the overall system cost. Additionally, off-grid systems have higher requirements for inverters and other equipment, as they must independently convert DC to AC and provide stable power, further driving up equipment costs.
Grid-tied: Grid-tied systems can rely on the grid as a supplementary power source, reducing the required capacity of the storage system and thus lowering energy storage costs. However, grid-tied systems require additional equipment such as grid-tied inverters, meters, and protective devices to connect to the grid and measure electricity, which adds some cost. Overall, the total cost is usually lower than that of off-grid systems.
Moreover, to avoid over-discharging or overcharging the batteries, the depth of charge and discharge may need to be limited, which can further reduce actual energy utilization efficiency.
Grid-tied: Grid-tied systems can feed excess electricity into the grid when the PV system generates sufficient power, reducing the waste of PV-generated electricity and improving overall energy utilization efficiency.
Additionally, the grid itself has the ability to regulate and optimize power distribution, enabling better integration and utilization of PV-generated electricity.
Maintenance is also more complex, requiring regular checks on the battery status (e.g., capacity, health) and PV module performance. If the system fails, professional repair is needed, which may result in household power outages during maintenance.
Grid-tied: In addition to the standard installation of PV modules and energy storage systems, grid-tied systems require connection to the grid, adhering to local utility regulations and safety standards for the installation and commissioning of grid-tied equipment.
This table clearly shows the differences between each photovoltaic power generation system in terms of their connection to the grid, the need for energy storage devices, application scenarios, system complexity and cost, and the stability and reliability of power supply. This helps us choose the appropriate system type based on specific application needs and conditions.
| Comparison Item | Grid-Tied Power System | Off-Grid Power System | Hybrid Grid Power System | Microgrid System |
|---|---|---|---|---|
| Connection to the Grid | Directly connected to the grid, can feed excess electricity to the grid or draw power from it. | Completely independent from the grid, does not rely on external power supply. | Can operate with or without grid connection, functions during grid outages. | Operates independently or with external grid connections, providing localized power solutions. |
| Requirement for Energy Storage | Usually does not require energy storage. Excess electricity can be sent to the grid. | Must include energy storage (e.g., batteries) to store electricity for nighttime or sunless periods. | Requires energy storage to operate independently during grid power loss. | May include energy storage for regional power management, improving efficiency. |
| Applications | Suitable for urban and suburban residential areas, commercial buildings, and large-scale solar farms. | Suitable for remote locations without grid coverage, such as mountainous or island areas. | Ideal for areas with frequent power outages or users requiring self-sufficient energy supply. | Suitable for industrial parks, universities, small towns, or regions balancing sustainability and self-sufficiency. |
| System Complexity and Cost | Simple structure, low cost, as energy storage is not required. | Complex structure, high cost due to the need for standalone control systems and energy storage. | Complex structure and high cost since it combines grid-tied and off-grid operating modes with energy storage. | Most complex and highest cost due to the need for diverse equipment and management of multiple energy sources. |
| Power Supply Stability and Reliability | Power supply relies on the grid; stable power output as long as the grid is operational. | Fully independent and does not rely on the grid, but power supply stability is limited by energy storage. | Combines the advantages of grid-tied and off-grid systems, offering high stability and reliability. | Ensures balanced regional power supply and greatly improves power stability and reliability. |
