Location: New Jersey, USA
System Size: 50kW
Modules: (360) 175-mono
Inverter: (1) 50kW
On the morning of 11 Feb 2013 as snow was melting off the array, the optimizer on module H5 detected three consecutive over-voltage events. This signature is indicative of a broken trace in a solar module. Without module-level electronics broken traces can go undetected and can create fire hazards in the form of arcing if reverse current conditions are present.
Reverse Current Leads to Arcing
Under normal operating conditions, a broken trace behaves similarly to a shorted bypass diode. However, when there is a harsh mismatch between strings (as in heavy shade or melting snow) the voltage runs in reverse through the weaker string. This is especially problematic when the inverter is not yet pulling current because the high voltage conducts through the cells and traces. If a trace is broken in this scenario it will lead to a high voltage low current arc inside the module.
Tigo Energy’s optimizer system detects safety hazards and implements a specific response for each type of event. In this instance, the MMU responded to repeated over-voltage events. Tigo Energy’s Management Unit (MMU) attempts to restart after one or two high-voltage events to confirm sustained high-voltage. After a third event, the MMU disables the system as part of the embedded safety features.
Once the MMU disables the system, the system owner, installer, and Tigo Support team are alerted to the problem. The system can then be diagnosed and must be manually turned back on once the safety hazard has been addressed. On this array, the MMU utilized this exact protocol to ensure the system was safe.
The Results—Arc Prevention
Using Tigo Energy’s module-level monitoring and alert system, a potentially dangerous situation was detected and diagnosed. The MMU effectively detected the signature of a broken trace and shut down the system. The Tigo Energy system prevented arcing and a potential fire.
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