Safeguarding solar modules
St. Thomas, US Virgin Islands. Credit: Jocelyn Augustino, FEMA

A solar module is a single photovoltaic (PV) panel that is an assembly of connected solar cells. Each element of the panel, if not handled correctly, is prone to damage, reducing its efficiency and rate of performance.

Having a clear picture of how damage occurs and prevention techniques is invaluable in keeping solar arrays performing optimally.

This article first appeared in ESI Africa Issue 4-2019.
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The solar industry, and specifically solar PV, has experienced exponential growth in the past decade. This is driven mainly by cost reductions of solar modules as well as the increase in the cost of conventional power generation technologies. In response to these market trends, the global PV industry has seen manufacturing volumes increasing exponentially.

Motivated by demand for PV, the industry players invested in a number of technology advances such as the introduction of glass-glass modules, dual/half cells, floating PV, and bi-facial PV. Currently the vast majority of all existing and new module sales consist of crystalline silicon cell based modules, either poly/multi or mono crystalline. The rest of the market is comprised mainly of various thin film PV technologies.

Regardless of the type of module used, there is always the chance of damage as the shipment travels from the manufacturer to your PV plant or rooftop.

Part one of this article presents four case studies outlining module damage scenarios and preventative measures. Part two of the article will be published in ESI Africa Issue 5 2019.

Case study: Humpty Dumpty

Setting the scene: Two pallets of PV modules fell from a three-metre high shelf in a warehouse. The one pallet rolled on its side, but remained on the shelf, while the other pallet tumbled to the ground (Figure 1). 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 (Figures 1 and 2). The remaining modules in the same box had no visible damage.

The insurance company agreed to cover replacement of the four damaged modules. Luckily, the owner of the modules was educated on PV microcracks 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 (Figure 3 and 4).

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: Dead man walking

Setting the scene: The rooftop solar PV market in South Africa is in a growth phase. Similar to any new and fast-growing industry, implementing these two items will secure the market’s sustainability: 1) considerable training and knowledge transfer is required, and 2) new standards and regulations are required.

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 trod on, 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 study: Sunscreen

Setting the scene: Conventional crystalline silicon PV modules consist of the solar cells laminated in an encapsulant material. The laminate is mounted between a glass front side and a back sheet (typically white coloured). The back sheet is a crucial component of the PV module, designed to protect the inner components of the module from external stresses. Made from various materials, some better than others, it also acts as an electrical insulator with the purpose of protection from ultra-violet radiation, and humidity and vapour penetration.

There are several cases in South Africa where large quantities of PV module back-sheets fail. Typical failure includes yellowing or browning of the back sheet, or more severe, cracking of the back sheet. The latter leads to water ingress into the junction box and corrosion of the conductive components.

This can be prevented by informing solar developers of the various back sheet materials available on the market. Armed with this information, developers can procure modules that use high quality back sheets or can specify this when negotiating a large order (Figure 7).

Case study: Head winds

GeoSUN has been involved with several projects in South Africa and other African countries where solar PV plants experience storm damage. 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 (Figure 9). 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.

Modules en route to your door

Impact-free transportation is crucial to ensure PV modules arrive in good condition at their destination. Figure 6 summarises the typical path from the factory to the final point of installation. Here you are given a visual on the numerous times modules are handled and the various transportation modes undertaken before reaching your project site.

Figure 6: The route your solar PV modules are likely to take is long and arduous. Credit: GeoSUN Africa

In the event that pallets containing modules are damaged, the modules can be tested at the location where the damage occurred. This is best done by using a mobile EL test device. When a large number of pallets are tested, one test methodology suggests testing the two outer modules of each box. If no damage is found, it can be assumed that the rest of the modules in the box are fine.

It doesn’t end here – in the next edition of ESI Africa we will look into another four areas in part two of Safeguarding your solar PV modules. ESI

About the author
Riaan Meyer is the managing director of GeoSUN Africa, a Stellenbosch University spin-off company established in 2012 and active throughout the African continent. His work focuses on solar resource assessment and PV module testing and inspection. GeoSUN collaborates with a spin-off company from the Nelson Mandela University in Port Elizabeth, PVinsight, to provide PV test-related services.