Rapid Shutdown & Solar Safety

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As cities and states adopt the NEC 2017 (National Electric Code), solar installers are searching for great module-level rapid shutdown solutions. In this live interview with Chris Connell, head of solution management for Fronius USA, we will explore the issues that matter to solar installers/developers, project/facility owners and first responders. Rapid shutdown devices and systems should:

  1. Be safe and reliable in an emergency
  2. Provide accurate arc fault detection and proper shutdown response
  3. Offer fewer connection points for less arc risk
  4. Be cost effective and durable

Since module level shutdown is for firefighter safety, solutions have to be reliable. When rapid shutdown is activated, the rapid shutdown devices must reliably switch and de-energize the array.

Electronic components can create electrical noise. With today’s rapid shutdown devices, the noise levels can increase significantly and interfere with proper arc fault detection. If the electrical noise created by rapid shutdown devices (e.g., from optimizers switching frequencies) creates signals that look like real arcs, the AFCI algorithm has difficulty discerning a real arc. This noise increases the likelihood of nuisance tripping or even worse, of not detecting a real arc.

Studies conducted by Fraunhofer Institute in Germany and BRE National Solar Centre in the UK concluded that DC connectors are a main cause for serial arcs in a PV array. Any rapid shutdown solution that significantly increases the number of connection points can add risk to the system. There are two main causes of DC connector faults: Installation errors and lack of a DC connector standard.