AXIS Explores
PV modules
Overview
PV modules may be monofacial (PV cells on one side) or bifacial (PV cells on both sides). Monofacial modules dominate the market currently but bifacial offer higher energy yield per panel and are becoming more popular. Monofacial modules could be of crystalline silicone type or thin-film type.
'Thin-film' modules are flexible and appear not to experience microcracking, however they require more surface area per watt generated.
The fasteners used to attach the PV modules to the support structures play an important role in the structural cohesion of the units. Poor fastening or low quality materials can have outsized consequences.
It’s critical that the junction boxes on the reverse side of the modules and associated wiring connections are of good quality. Poor quality can lead to increased downtime.
Types of failure
Microcraking
Whether glass/foil or glass/glass, crystalline silicone (c-Si) modules can experience microcracking. Microcracks are microscopic cracks in the solar cells which are typically invisible to the naked eye.
Microcracking causes a reduction in the power output of the module. This may be caused by:
- Thermal cycling (large temperature differences that push the working capacity of the solar cells)
- Heavy snowfall
- Winds and hailstones (NATCAT perils)
- Incorrect or loose fasteners
- Mishandling during transport, storage and installation can also result in microcracks.
Microcracks can be detected via Electroluminescence (EL) testing, which makes it possible to detect any internal damage to the PV module.
Types of failure
Junction boxes
Junction boxes connect the module strings together and are located on the underside of the modules.
Most junction box failures are caused by either bypass diodes failures or faulty connections inside the junction box (poor solder joints which can lead to hot spots or electrical arcing).
Bypass diodes prevent back current which occurs when some cells are in the shade or dirty and often fail over time due to overheating or defects.
When one diode or circuit connection fails, one of the three substrings of the module stops generating. The failed substring has a higher temperature which can be identified with a thermographic scan.
Modern modules now use more advanced long lasting diodes and potted (i.e. sealed) junction boxes. This improves water-tightness but makes repairs more difficult.
