Solar panels are designed to produce electricity for up to at least 25 years. However, despite the need for reliable solar panels, some manufacturers still cut corners around production costs in order to compete on price. This means the influx into the market of solar panels that are bound to fail before their expected lifetime.
A defective solar panel will reduce the productivity of it array by up to 20%. Keeping in mind that due to poor or in some cases, no efforts by regulatory bodies and authorities, Nigerian markets are susceptible to the influx of substandard products, it is therefore very important to bear in mind that there are as good solar panels in the market as there are defective ones and potentially-defectives ones, and that one can be duped into investing on defective products.
Defects in solar panels may include the following:
1. Hot Spots
Solar cells generate an electric current from incident sunlight. The resistance in the cells converts the electricity generated by the cells into energy losses in the form of heat. Hotspots on panels are mainly caused by badly-soldered connections. Badly-soldered connections cause low resistance in the part of the panel that receives the power generated by the cell. This ultimately leads to a short-circuit which reduces the performance and lifespan of the panel. Generally, other structural defects in the cells such as cracks, and mismatched cells can lead to higher resistance and become 'hot spots' in the long run.
The long term effects of hot spots include burnt marks that degrade solar cells and backsheets. They may eventually lead to fire outbreaks if left unchecked.
Micro-cracks, as suggested by the name, are inconspicuous tears in the solar cells. Micro-cracks can occur during their manufacture, but also during shipping and also when poorly handled during installation.
While micro-cracks may not necessarily result in immediate production loss, they however can grow over time, for example due to thermal tension, or under the influence of seasonal and weather conditions. Larger micro-cracks will damage the solar cells and by so doing reduce the performance of the panel by about 2-3%.
The panel’s performance decreases in direct correlation to the number of broken cells. Multiple busbars are often installed in the more expensive panel brands in order to mitigate this problem.
3. Snail Trail Contamination
Snail trail is a discolouration of the panel which usually only manifests after a couple of years of production.
Snail trails have multiple causes, but a major cause can be attributed to the use of defective front metallization silver paste in the solar cell manufacturing process. Defective silver paste can lead to moisture in the panel, and as a result of this moisture, an oxidation can occur between the silver paste and the EVA film leading to the release of silver oxide, vinegar and hydrogen. The effect of this reaction is fed from the back of the panel to the front of the panel, and causes a chemical breakdown on the front of the panel. This becomes visible as ‘snail trails’, resulting in a reduction in the panel’s performance.
After studying patterns across many solar manufacturing plants, it was broadly concluded that mere existence of snail trails by itself does not necessarily affect power generation. However, they have been assessed to reduce the performance of panels when they arise from or, when with the presence of water vapour, form along micro-cracks. It gets worse when the underlying solar cells are broken. In that case, the cells can continue to generate electric current along the cracks, causing localised heat that breakdown the cell surface and EVA film in which the cells are encapsulated.
Solar cells are encapsulated in a specially designed polymer (ethylene vinyl acetate, EVA for short, in virtually all cases). These cells are placed between two polymer films in a vacuum and under heat and compression with the help of a special type of lamination machine laminated together. Delamination is the detachment of the laminated components. It occurs if the lamination was not done properly, or inferior plastics was used, if the laminating machine is inferior and the laminating process was poorly regulated for pressure and temperature, if the film was too short and if the glass and the plastic were are not compatible.
The goal of the lamination is to protect the cells from adverse weather conditions and to prevent moisture and dirt from entering the solar panel. In addition, they help to soften the impact of shocks and vibrations and therefore protect the solar photovoltaic cells and the busbars and fingers. Delamination can cause moisture to enter the cells or bubbles to occur within the cell. Moisture leads to the corrosion or rusting of the solar cells and/or other components which becomes even more visible as darker spots on the panel.
5. Cracked Backsheet
Another way moisture and dirt can enter a solar panel is through a cracked backsheet. If poor materials are used in making their backsheet, it is most likely that they will degrade after a while exposing the solar cells to intense UV radiation and temperature variations every day.
6. Brown Spots
Brown spots occur when there is a change in colour of the EVA film. This happens when certain additives used to prevent browning and enhance UV resistance start to disappear. A solar panel can also brown if it is stored or handled. It can cause bleaching and blistering at the EVA film and the solar backsheet, resulting in the rusting of the solar cells.
7. PID Effect
PID stands for ‘Potential Induced Degradation’. This problem can arise when a voltage difference occurs between the panel and the grounded frames. (Read all about the considerations for grounding a solar panel-inverter-battery system here.) This can lead to an unwanted migration of the charge carriers. The high voltage difference between the grounded frames and solar cells or between the solar panel and the inverter may be too much for low quality solar cells to handle forcing them to begin to deteriorate.
If for safety reasons, the solar panel is earthed, it can cause a harmful potential difference between the earthing and the voltage generated by the panel. In some cases, this generates a voltage which is partly discharged in the primary power circuit. The consequences of this effect are an on-going reduction in performance and accelerated ageing of the solar panel.
In case of high voltages due to long string connections, the PID effect can also occur even more heavily. High humidity and temperature also accelerate this process. Dust and glass degradation during which Sodium ions are released may also catalyse the PID phenomenon.
PID can lead to performance loss of up to 10%. This makes PID a highly critical concern, because it generally only develops months after the installation of the system. Moreover, unlike other module defects, such as delamination, hotspots, cracking or yellowing of EVA parts, the PID is not detectable with the naked eye.
8. Corrosion/Rusting of the Metal Parts of the Solar Panel
Rusting of the metal conducting parts of the solar panel usually starts at the edge of the panel and can spread across the rest of the panel. This leads to significant reduction in the panel’s production. The panel’s production will decrease in direct correlation to the size of the rusted areas. Frameless/thin-film PV panels and panels manufactured based on glass substrates in particular can also suffer from moisture and corrosion problems.
9. Dust Build-Up
The accumulation of dust on the solar cells panels lowers the efficiency of the solar
cells day by day especially in the regions with high rate of dust, low frequency and intensity of rain. The accumulated dust on the solar cells panel blocks the cells from the sun’s rays and act as a screening effect which decreases the performance of the solar cells over time until the cell panels are cleaned either manually or by rain. The
Also, when solar panels are placed on rooftops at a gradual slope, their frames may collect rainwater into a stagnant pool. After the water has evaporated, a dust residue is left behind which creates unwanted shading and reduces the energy production of the solar cells.
10. Defective Junction Box
The junction box is a small weather-proof enclosure in the form of a black box located on the rear side of the panel. It is needed to securely attach the cables required to interconnect the panels. The junction box is important as it is the central point where all the cells are interconnected and must be protected from moisture and dirt.
The junction box contains bypass diodes that keeps electricity flowing in one direction and prevent it from feeding back to the panels. A burnt bypass diode or connector can leave the panel in open circuit and stop transferring energy outward altogether. If water or dust seeps into the junction box enclosure, the bypass diodes inside can become short-circuited and burn out.
Defects in the junction box have been known to start fires.
11. Unevenness In Colour
Solar panels are designed to be aesthetically-pleasing and to easily integrate into roofing systems. This is a special point in their design mostly in Class A modules, that is, modules that are built for residential installations. It is therefore very important to invest in panels in which the manufacturers used only solar cells that are uniform in colour.
At SolarKobo we help our clients make the best possible choice of solar panels and other alternative energy products like batteries, charge controllers and inverters. We also have university-trained engineers that provide high quality installations services on order.