Microcracks are small cracks in solar cells that are impossible to see with the naked eye but really impact the performance of your solar energy system and investment.
Photovoltaic cells, in their basic form, are relatively thin and can be fragile to any kind of pressure or stress, leading to damage caused by cracking which in turn results from the inherent weakness of the silicon cell material. The integrity of the cells does change with different manufacturers and as a response to different known location requirements. When they occur, micro-cracks can vary from small sections of the cells to the full length of the cells and are not always visible from the naked eye.
The three main microcrack causes are manufacturing, delivery/installation of the panels and the operational lifecycle of the panel, including environmental factors.1
Manufacturing defects are usually caused by poor quality materials or process controls, which means the cells become exposed to excessive stress or temperatures as well as poor quality manufacturing and production equipment. These should and can be easily mitigated by the introduction of strict quality assurance checks being put in place. Through greater focus on the manufacturing processes over the last decade there is now a clear understanding of Tier 1 and Tier 2 manufacturers when developers are considering procurement versus cost and quality.
In the delivery stage, damage to the cells is normally incurred as a result of incorrect packaging, unsuitable transportation methods and poor handling techniques. All of these can be mitigated to a large degree by designing packaging with enough protection and padding to ensure that the correct protocols are followed while shipping and storing. While in the installation phase, damage can be caused by improper handling of the modules, accidental bumps and/or drops and excessive force, twisting while installing within the frames and installers walking on panels. It’s a common feature with many insurers, who have reported finding that human error (workmanship) resulting from inexperienced construction crews is still often the root cause.
The most common cause of microcracking is following installation of the panels and during their operational lifetime when they are exposed to external environmental factors. This includes fluctuations of temperature between day and night, constant wind fatigue stresses, heavy snowfall creating weight pressures and, of greatest concern, hailstorms. These can all place the cells under extreme duress, which can lead to microcracks occurring2.
However, it must be stressed that the existence of a microcrack does not mean that the PV cells or panels will not function to their designed specification. With operational life expectancy of up to 25 years, it is often difficult to identify the difference between the known or predicted degradation of the panels. However, additional degradation in panel performance (the responsibility of the manufacturer under warranty) or damage that has arisen from sudden external environmental events as identified, would not be the responsibility of the manufacturer. As noted, continual short exposure to external factors, which might normally be considered to be covered by traditional all risks of physical loss or damage policies, may not be identified at the time of occurring; instead, a fatigue stress event is created, which only manifests itself over a longer period. Insurance generally requires a sudden and identifiable event for damage to be considered.
The Solar Photovoltaic (PV) industry has developed new techniques for crack detection, such as the Resonance Ultrasonic Vibration (RUV) to detect in-line non-destructive cracks that may occur during the manufacturing process3. Additionally, there is the Electro Luminescence (EL) or the Electro Luminescence crack detection (ELCD) which is one of the most applied quality testing imaging methods. The EL method scans the surface of the PV modules in a method which is very similar to something like an X-Ray. Using the EL method, the pictures taken allows us to peer directly into the inner structure of the solar cells of a PV module to reveal any inherent defects and micro-cracks within.
According to Sundling4, over the past decade the practice of EL imaging has advanced dramatically and now allows owners or operators of Solar PV systems to identify any modules with cell damage that are likely to underperform against the stated design specification. The evolution of this technology means that it is no longer restricted to highly controlled indoor laboratory environments; it can therefore be used in the field during the daytime without unnecessary cost or effort, making it easier to test these panels on a more regular basis.
When microcracks are present, they cause an electrical separation which in turn causes parts of the cell to remain inactive. Quantifying this to a specific level of power loss is quite challenging, as there are several other factors that play a role. It has been shown that modules that have microcracks can still meet the warranted power over the module’s lifetime, so rejecting every module that contains a microcrack is not necessary5.
Nonetheless, it is almost impossible to avoid microcracks in the long-run; left undetected, it is estimated that the economic impact of microcracks, including repair/reinstatement costs as well as the cost of loss energy productions, is around €6 per kilowatt per year, meaning that overall annual losses would be well into three-digit millions every year6.
There is now enough evidence to suggest that microcracks, whist inevitable, can be mitigated by good risk management. The Renewable Energy insurance market has experienced several high-profile natural catastrophe losses in recent years; this has firmly placed Solar PV projects under insurers’ scrutiny for microcracking from external environmental factors. This includes direct and indirect microcracking losses from various issues, such as wind damage resulting from hurricanes and, more recently, large unnamed storms, poor installations resulting from contractor workmanship issues and hailstorm damage. When losses occur with increasing frequency and severity, insurers will seek to respond by reducing cover and increasing prices. Coupled with the hardening of the insurance markets globally, insurers are looking to limit their exposure by the application of microcracking endorsements such as the example reproduced in Figure 3 to the left.
Consequently, there is increased reliance on securing proof that the panels remain inherently free of microcracks at the appropriate times. This might be after production, upon delivery or during the panel commissioning/acceptance testing before acceptance by the facility owner. Evidence of the panels being microcrack-free can then be used as a baseline, if it is thought that damage occurs later; or alternatively if the defence is to be that the damage is a pre-existing issue, the evidence can point to which party should take responsibility for rectification.
A key issue is that the damage must have occurred following an insured event - i.e. damage needs to have occurred. There is a need for an agreed methodology to determine the conditions at some point or points in time, through an agreeable test method. Post-event testing costs are still not cheap, even if costs are coming down; as a result, we are seeing the introduction by some insurers of monetary limits for testing costs. We are also seeing the market introduce conditions which stipulate that insurers will only accept that there has been insured damage if there is an identifiable event which results in damage to more than 25% of the exposed panels.
This market response highlights that microcracking is a major concern for the solar industry and its relationship with the insurance market. However, with several Tier 1 manufacturers now investing heavily into research and development, we are seeing cells which are much less vulnerable to cell cracking - a welcome development.
Furthermore, the advancement of the EL imaging ability will assist owners and developers to be able to engage with more active monitoring of their sites, identifying early any signs of trouble (which may not be visible to the naked eye) and allowing them to more clearly identify the causation and relevant party for rectification.
Because of both of these factors, we believe that future relationship between the solar industry and the insurance market remains promising.
John Abraham is an Account Director in the Renewable Energy division at Willis Towers Watson in London. John.Abraham@WillisTowersWatson.com
1 Ed. (2018, October 8). Solar Panel Micro Cracks (Tier-1) Exposed! https://review.solar/solar-panel-micro-cracks/ 2 Niclas. (2012, December 25). Solar panel micro cracks explained: https://sinovoltaics.com/quality-control/solar-panel-quality-an-introduction-to-micro-cracks/ 3 Dhimish, M., Holmes, V., Dales, M., & Mehrdadi, B. (2017, June). The effect of micro cracks on photovoltaic output power: case study based: http://eprints.hud.ac.uk/id/eprint/33463/1/Effect%20of%20micro%20cracks%20on%20photovoltaic%20output%20power%20case%20study%20based%20on%20real%20time%20long%20term%20data%20measurements.pdf 4 Sundling, A. (2019, November 19). PVEL - Independent Test Lab: https://www.pvel.com/field-el-testing-pv-modules-benefits-for-asset-owners/ 5 Köntges, M., Kajari-Schröder, S., Kunze, I., & Jahn, U. (2011, September). Crack statistic of crystalline silicon photovoltaic modules. Retrieved from 26th European Photovoltaic Solar Energy Conference and Exhibition. https://www.researchgate.net/profile/Sarah_Kajari-Schroeder/publication/236152832_Crack_Statistic_of_Crystalline_Silicon_Photovoltaic_Modules/links/00b7d533933214bf10000000/Crack-Statistic-of-Crystalline-Silicon-Photovoltaic-Modules.pdf 6 Hutchins, M. (2018, December 26). Filling in the (micro)cracks. https://www.pv-magazine.com/2018/12/26/filling-in-the-microcracks/
