The "PV System Doctor" is an advanced Operation & Maintenance (O&M) service developed and implemented by SERIS that provides a comprehensive "health check" for PV systems. The service aims at providing timely identification of under-performance of PV assets and proactively evaluating solutions to mitigate risks and prevent future financial losses. (Please refer to a technical article) Target customers are typically PV system owners and operators, investors and insurance companies. The three main reasons for calling the PV System Doctor are:
Remote monitoring solutions can provide a quick insight into the quantitative performance aspects of the PV modules or the entire PV system. However, the root cause of losses in a system often remains a question unanswered without an onsite inspection. Therefore, it is essential for the system doctors to carry out certain on-site diagnoses to find the reasons for the under-performance and develop solutions to improve the health status of the PV systems. In addition to I-V curve analysis, visual inspection and thermographic analysis of PV systems, which provide initial hints about the module defects, SERIS provides in-depth diagnosis of various PV module faults such as potential-induced degradation (PID) and micro-cracks, which are often the root causes of power losses. SERIS’ PV System Doctor employs highly specialised mobile daytimeluminescence imaging techniques and UV fluorescence imaging techniques to inspect the quality of PV modules either individually or as a complete string - without removing them from the frames or from the site. The daytime luminescence system is an in-situ non-destructive technique that provides information on material or electrical defects in PV modules or strings. The equipment is capable of performing both daytime electroluminescence (DEL) and daytime photoluminescence (DPL) imaging. The pictures in Figure 1 show a representative comparison between optical, infrared (IR) and DEL images of a silicon PV module with cracked cells, which were captured on-site at the same time under identical irradiance conditions for comparative analysis. It can be clearly seen that the DEL image provides a much greater wealth of information compared to the IR image, which does not show any abnormally high temperatures of the affected areas.
Similarly, Figure 2 shows a representative comparison of DPL and DEL images captured on-site during daytime for PV modules of PV systems installed in the ASEAN region in the last 5-10 years. The DPL images (a, b) show darkened cells, which indicates degraded material quality of the cells, potentialinduced degradation, and/or intrinsically or mechanically induced shunts. The DEL images (c, d) show localised dark cell areas and streaks of dark lines near the busbars and fingers, which is the result of electrical shunts and electrical interconnection faults in the PV modules. DEL allows to detect a multitude of defects such as micro-cracks, electrical shunts, broken contacts and interconnects, and many more. Such defects lead to under-performance of the affected PV modules and eventually cause energy yield losses in the PV system.
In addition, UV fluorescence (UVF) of ethyl vinyl acetate (EVA) enables the detection of snail trails and cell cracks. Due to its ease of use, the UVF imaging technique can be employed to scan large parts of a PV system, with a measurement throughput of more than 100 modules per hour. Figure 3 shows that cell cracks are clearly visible in the UVF image (right), whereas the normal visual inspection image (left) has to be magnified and carefully scrutinised to detect the cracks.
The possible root causes for sub-optimal performance of PV systems include component defects, design-related issues, and issues arising from a poor installation. What is often underestimated is the severe financial impacts arising from underperforming PV assets.
a) Scenario 1: A collective under-performance of one quarter of the installed PV modules (only reaching 50% of the rated power); Using a 1 MWp rooftop example in Singapore, Figure 4 shows the impact of this module under-performance on the financial performance of the system and the energy output over its entire lifetime, as well as the positive impacts of rectification works.
b) Scenario 2: An under-performance triggered due to the premature failure of a component (modules or inverter) causing a drop in performance ratio. If the power plant owner needs to pay for the replacement of the faulty modules/inverter, the output can be restored, however, the internal rate of return (IRR) remains sub-optimal. If the component warranty can be claimed successfully in a timely manner, then the output is restored and the IRR is also restored to the expected level. Such detailed cost-benefit analyses will be performed to decide whether or not potential rectifying measures are worthwhile from a financial point of view.
Case Study for Utility-scale PV System: Click Here
Case Study for Industrial Rooftop PV System: Click Here
Case Study for Commercial Rooftop PV System: Click Here
Case Study for Off-grid PV System: Click Here
We welcome any service requests, research collaborations and technical consultations.
For further information, please contact:
Dr Darryl Wang
Head, Asia PV Quality Assurance Centre