Since the advent of photovoltaic power generation systems, fire accidents caused by photovoltaic power stations have occurred from time to time around the world. Against this background, photovoltaic module-level rapid shutdown has been understood and valued by more and more people...
Solar Rapid Shutdown of photovoltaic systems, as the name suggests, is to quickly shut down the connection between each photovoltaic module. This concept was proposed by the National Electrical Code (NEC) of the United States. As early as 2014, the NEC2014 690.12 "Module-level Self-Shutdown Solution" standard was released, which made requirements for the rapid shutdown of photovoltaic systems.
In the 2017 version of NEC690.12, strict requirements were made for this rapid shutdown - with a distance of 305mm to the photovoltaic matrix as the boundary, within 30S after the rapid shutdown device is activated, the voltage outside the boundary range is reduced to below 30V, and the voltage within the boundary range is reduced to below 80V, that is, it is required to achieve "module-level shutdown". In the latest 2020 version of the standard, the term "rapid shutdown" is further modified and expanded, and a "PV hazard control system" is proposed. The new standard requires that the PV system has a "PV hazard control system" to make the PV system a controllable state in critical situations. In other words, the "PV hazard control system" can be used to achieve component-level shutdown, and within 30 seconds after the rapid shutdown is started, the voltage within the boundary range is reduced to below 80V.
Principle of Photovoltaic Module-Level Rapid Shutdown
Working mode of photovoltaic module-level rapid shutdown
The principle of rapid shutdown at the photovoltaic module level mainly includes two aspects: shutdown method and shutdown principle.
There are two main ways to quickly shut down the photovoltaic module level: mechanical shutdown and electrical shutdown.
1. Mechanical shutdown: Mechanical shutdown is to disconnect the photovoltaic module from the circuit through a mechanical device to stop the output power of the solar panel. Common mechanical shutdown methods include switches, knife switches and circuit breakers. The advantages of mechanical shutdown are simple structure and high reliability, but the operation is relatively slow and requires manual intervention.
2. Electrical shutdown: Electrical shutdown is to disconnect the photovoltaic module from the circuit through electrical components to stop the output power of the solar panel. Common electrical shutdown methods include relays, thyristors and power transistors. The advantages of electrical shutdown are fast operation speed and high precision, but external power supply and circuit control are required.Shutdown principleThe principle of rapid shutdown at the photovoltaic module level mainly includes two methods: voltage shutdown and current shutdown.
1. Voltage shutdown: Voltage shutdown is to automatically disconnect the photovoltaic module from the circuit by measuring the output voltage of the photovoltaic module. When the voltage exceeds the set value, the photovoltaic module is automatically disconnected from the circuit. This method can effectively prevent damage to photovoltaic modules due to excessive voltage. The key to voltage shutdown is to monitor the voltage and compare it with the set value. When the voltage exceeds the set value, it is shut down by electrical or mechanical means.
2. Current shutdown: Current shutdown is to measure the output current of the photovoltaic module. When the current exceeds the set value, the photovoltaic module is automatically disconnected from the circuit. This method can effectively prevent thermal damage or reverse flow to the photovoltaic module due to excessive current. The key to current shutdown is to monitor the current and compare it with the set value. When the current exceeds the set value, it is shut down by electrical or mechanical means.
In addition to voltage shutdown and current shutdown, the two can also be combined for linkage shutdown. For example, when the output voltage of the photovoltaic module exceeds the set value or the output current exceeds the set value, the shutdown operation is performed at the same time to more effectively protect the photovoltaic module.
Photovoltaic module-level rapid shutdown is to disconnect the photovoltaic module from the circuit by mechanical or electrical means to stop the output power of the solar panel. The shutdown methods include mechanical shutdown and electrical shutdown, and the shutdown principles include voltage shutdown and current shutdown. The application of these shutdown methods and principles can effectively protect photovoltaic modules, extend their service life, and ensure the safe and stable operation of photovoltaic systems.
Why is the rapid shutdown of photovoltaic modules so important?
There are many reasons for fires in photovoltaic power plants. The equipment with the greatest risk of fire include inverters, junction boxes, cables, and modules. As long as it is an electrical system, there is a risk of fire due to current. In addition, with the advancement of photovoltaic technology, the power level and current voltage of photovoltaic products have been continuously improved. The photovoltaic system has been upgraded from the initial 600V design to 1000V, and recently gradually upgraded to 1500V. Higher voltages are more likely to cause fires. Fires in photovoltaic power plants pose a great challenge to firefighters. After a fire occurs in the system, high voltages of hundreds or even thousands of volts will still be generated. If firefighters rush to rescue, their lives will be threatened. With the module-level rapid shutdown function, firefighters can quickly cut off the connection between modules and rescue the power station.
Conclusion
Although it is still difficult to fully promote the installation of component-level rapid shutdown devices in most parts of the world due to a series of factors such as cost, it must be said that component-level rapid shutdown is a very important function for the safety of photovoltaic power plants. I believe that with the continuous advancement of technology, the popularization and implementation of safety regulations, and the gradual strengthening of safety awareness, this technology will be used more and more to protect more power plants.
