How can the excess electricity be "sold back" to the power grid except for its own use?
The core of the answer lies in the network-line inverter.
It is not just a "converter" that converts direct current into alternating current, but the core equipment responsible for energy coordination, grid synchronization and security protection in the entire grid-connected photovoltaic system.
This article will start from scratch. The system will clearly explain the working principle, key technologies,application scenarios and selection points of the network-onned inverter to help you truly understand:
How does the grid-connected inverter send solar energy back to the power grid safely and stably?
I. Why do we need to know about network-line inverters?
When the solar photovoltaic system is connected to the public power grid, it is not "plugging in and using it".
Solar panels generate direct current (DC), while households and power grids use alternating current (AC);
At the same time, the power grid has extremely strict requirements for voltage, frequency, phase and security protection.
Grid tie inverter is the "bridge" between the photovoltaic system and the power grid. At the same time, it bears the burden of:
- DC → AC power conversion
- Real-time synchronization with the power grid
- Power generation efficiency optimization
- Network security and protection
The summary in one sentence is:
A grid-connected inverter is not an ordinary inverter, but a power generation coordinator that "understands the grid rules".
II. What is a network-lined inverter?
2.1 Basic definition of network-line inverter
Grid-Tie Inverter is essentially a highly intelligent power conversion device, which is responsible for connecting solar modules and public power grids, and is the "hub" of the entire grid-connected photovoltaic system. It mainly undertakes two key tasks.
One is the conversion of electricity. Solar panels generate direct current, while alternating current is used in homes and commercial buildings. Grid-lined inverters will efficiently convert these direct currents into directly usable alternating current, providing stable power for all kinds of electrical equipment.
The second is accurate synchronization with the power grid. The grid-onned inverter can monitor the status of the power grid in real time and automatically adjust the voltage, frequency and phase of its own output to keep it consistent with the public power grid. Because of this synchronization ability, the system can not only give priority to solar power supply, but also take electricity from the power grid when the light is insufficient, and even safely return the excess power to the power grid.
Compared with off-grid systems that require a large number of energy storage batteries, grid-connected solar systems directly rely on the public power grid as "virtual batteries", with a simpler structure and lower initial cost, so they have become one of the most common and more cost-effective solar solutions for urban and suburban residences.
The basic energy path is as follows:
- Solar panels → grid-connected inverters → household electricity / public power grid
2.2 The difference between network-on, off-network and hybrid inverter
| Type | Grid-tied | Battery required | Typical applications |
|---|---|---|---|
| Grid-tie inverter | Yes | No (optional) | Residential / C&I grid-connected PV |
| Off-grid inverter | No | Yes | Areas without utility grid |
| Hybrid inverter | Yes | Yes | Grid-connected systems with storage |
What needs special attention is:
The pure net-line inverter will automatically shut down when the power goes out.
This is a regulatory requirement, not an equipment failure (detailed later)
III. How does the network-line inverter work?
3.1 From DC to AC: Electrical Energy Conversion Process
Solar panels generate direct current under light, but this kind of electricity:
- The voltage is unstable
- The current changes with the light.
- It cannot be directly used by the power grid or household appliances.
The grid-lined inverter converts unstable direct current to standard alternating current through the internal power electronic module, and accurately controls the output waveform to meet the requirements of the power grid.
3.2 Maximum Power Point Tracking (MPPT)
Almost all network-onverters have built-in MPPT (Maximum Power Point Tracking) technology.
Its function is:
- Real-time monitoring of voltage and current changes
- Automatically find the "best power generation point" for solar panels
- Continuously optimize the output under light changes, shadows and temperature changes
The simple understanding is:
MPPT allows solar panels to "generate more electricity and not waste" as much as possible in any environment.
Previous articles：
What is an MPPT Inverter ?
IV. How to send solar power back to the power grid safely and stably?
This is the essential difference between network-line inverters and ordinary inverters.
4.1 Synchronization mechanism with the power grid
Before the network inverter is networked, it must do the following:
- The voltage is the same
- Consistent frequency (50Hz / 60Hz)
- Phase synchronization
As long as there is any deviation, the inverter will not allow the network.
4.2 Protection against isolated islands
This is one of the most important security mechanisms in the network-connected system.
When there is a power outage in the public power grid:
- The network-line inverter will detect anomalies at the millisecond level.
- Stop sending electricity to the power grid immediately.
There is only one purpose:
Prevent reverse power transmission and ensure the safety of maintenance personnel and equipment.
Therefore:
The grid-lined inverter will not continue to supply power when the power is out. This is a "safety feature", not a shortcoming.
4.3 Electricity quality and networking standards
Compliant grid-tied PV inverter usually needs to meet:
- IEC / IEEE Grid-tined Standard
- Power quality control (harmonics, power factors)
- National or regional power grid specifications
This is also the reason why it is difficult for low-quality inverters to pass the network audit.
V. Analysis of key functions and parameters of network-lined inverters
| Parameter | Meaning | Practical Impact |
|---|---|---|
| Rated Power | Maximum output capability | Determines system size |
| MPPT Channels | Number of maximum power points | Better for multi-oriented roofs |
| Peak Efficiency | Conversion efficiency | Directly affects energy yield |
| IP Rating | Dust & water protection | Essential for outdoor installation |
| Grid-connection Certification | Regulatory compliance | Required for legal grid connection |
VI. Practical application scenarios of network-lined inverters
6.1 Home roof photovoltaic system
- Spontane and self-use to reduce electricity bills
- Extra power is connected to the network
- Simple structure and relatively low cost
- It is the most common form of application at present.
6.2 Commercial / Industrial and Commercial Network System
- The system has a larger capacity.
- Multi-way MPPT is almost just a need.
- Stricter network-online standards and stability requirements
6.3 Public Buildings / Community System
- Centralized networking
- Unified monitoring
- Extremely high requirements for the reliability of equipment
VII. Grid-connected inverters are the "brains" of modern photovoltaic systems.
The Grid-Connerted Inverter Not Only Completes The Electrical Energy Conversion, But Also Undertakes The Undertaking Of:
- Power generation efficiency optimization
- Power grid coordination
- System security protection
In the grid-connected photovoltaic system, it is the real "hub equipment".
Only by choosing the right grid-connected inverter + scientific system design can every degree of solar energy truly create value.
If you are planning a home or industrial and commercial grid-connected photovoltaic system, understanding the working principle of grid-connected inverters will be the first step in making the right decision. Welcome to consult us, and the professional technical team will escort you!
