Micro Cracks - Know Your Module/2

This article presents three case studies outlining module damage scenarios and preventative measures.

Case 1: Drop Test

Two pallets of PV modules fell from a metre height. The one pallet rolled on its side, but remained on the shelf, while the other pallet tumbled to the ground. The warehouse personnel opened both boxes to assess the damage. The modules of the first pallet had no visual damage. Only four modules in the second pallet showed severe damage, with broken glass and bent aluminium frames. The remaining modules in the same box had no visible damage.

The insurance company agreed to cover the replacement of the four damaged modules. Luckily, the owner of the modules was educated on PV micro-cracks and requested replacement of all the modules, not just the visibly damaged ones. Before complying with the request, the insurance company would need independent test results to prove cell damage.

This would entail sending the modules to a laboratory for testing. The client realised that this could lead to a further dispute – if the test should discover further modules with damage, the insurance company could argue that these were the result of damage occurring during transportation to the laboratory’s facilities and not resultant from the original fall.

The client, therefore, opted for on-site module testing at the warehouse. A test method called electroluminescence (EL) was used, which allows for an image of the PV module to be captured from which cell damage can be assessed. The EL method is comparable with that of taking an X-ray image whereby information not apparent to the naked eye can be obtained.

All the modules underwent EL testing in the warehouse. The modules in the pallet that fell to the floor were all found to be severely cracked and were replaced by the insurance company. The modules in the pallet that rolled on its side were all found to be in good order and without any cell damage.

Case study 2: Walking

During the market’s initial phase of development many inexperienced people, typically from micro and small companies, trade in the industry without any training.

This training extends to basic facts, which include: “Do not walk on the modules.” When PV modules are installed, the cells inside the module typically crack, even though no visual damage is seen on examination. Installers should be educated, walking on modules should be avoided at all costs, and your PV system should be designed with walkways and other access routes to the modules in order to perform maintenance and cleaning.

Once a cell is cracked, its power output degenerates far more rapidly than usual – all solar module output decreases over time. Another challenge is that temperature changes between day and night cause thermal expansions and contractions, which pull apart the materials around the crack, exacerbating the problem.

Case 3: Headwinds

Damage occurs due to high wind speeds, which induce mechanical stress on the modules and cracked cells. Hail is another weather-related culprit that can cause havoc on a solar plant.

Recently a new method has been applied to inspect solar modules. The method entails using a special UV inspection light at night. This method is less time consuming than EL and hence more modules can be inspected. UV is currently not accepted for insurance claims, so a follow-up EL inspection of modules identified using the UV method is performed. The UV inspection method is, however, a very effective screening tool to locate modules for EL testing.

As the testing methods are getting evolved drones are also being used to conduct thermal imaging and this proves to be a very effective tool and time-efficient to identify and qualify the modules that need to be tested for further defects under the EL and UV test.