The safety of photovoltaic (PV) systems is of paramount importance. Rapid shutdown technology is an important measure to ensure the safety of PV systems. Module-level rapid shutdown (MLRSD) and string-level rapid shutdown (SLRSD) are two common rapid shutdown technologies that differ in their scope of action, implementation, and cost. This paper compares the two technologies to help readers choose the appropriate rapid shutdown solution.

rapid shutdown, module-level, string-level

Introduction

PV systems generate high direct current (DC) voltage during power generation, which poses a risk of electric shock. To ensure the safety of PV systems, rapid shutdown technology has been developed. Rapid shutdown technology can quickly cut off the DC voltage of the PV array in case of fire, electric shock, and other accidents, eliminating safety hazards.

Comparison of Two Rapid Shutdown Technologies

AspectModule-Level Rapid ShutdownString-Level Rapid Shutdown
Scope of actionEach moduleEach string of modules
ImplementationInstall rapid shutdown devices on the DC side of each moduleInstall rapid shutdown devices on the DC bus or AC side of the PV array
CostHigherLower
AdvantagesHigher safety, can effectively reduce the risk of electric shockLower cost, simple installation and maintenance
DisadvantagesHigher cost, complex installation and maintenanceLower safety, cannot completely eliminate the risk of electric shock

 Application Scenarios

  • Module-Level Rapid Shutdown is suitable for PV systems with high safety requirements, such as:
    • PV systems installed on roofs and other areas where people are easily accessible
    • Large-scale ground-mounted PV power plants
  • String-Level Rapid Shutdown is suitable for PV systems that are more sensitive to cost control, such as:
    • Small PV systems
    • PV systems with low safety requirements

Conclusion

Module-Level Rapid and String-Level Rapid Shutdown each have their own advantages and disadvantages. Users can choose the appropriate rapid shutdown solution based on their actual needs.

Keywords: PV system, rapid shutdown, module-level, string-level, safety