Temperature coefficient playing key role in PV system performance – IEA report

The latest in a line of reports from the IEA (International Energy Agency) into longer-term analysis of PV systems highlights the role of ambient temperature in the long-term performance of PV systems. 

Although temperature coefficient related performance degradation has been well documented in typically hot and humid climates such as India with First Solar in white papers published in Photovoltaics International, PV Tech’s sister technical journal, the latest IEA study “Report IEA-PVPS T13-05:2014 Analysis of Long-Term Performance of PV Systems,” highlights the performance ratio (PR) impact of higher ambient temperature in countries such as Italy, showing meaningful statistical differences up and down the country. 

The study showed that despite high irradiance levels in the south and middle regions of Italy, southern located PV systems (small and large) typically generated a lower performance ratio than plants in the middle region of the country due to higher ambient temperatures. However, both regions still outperformed northern located PV systems due to higher irradiance, despite cooler northern ambient temperatures. 

The study also noted in more northerly regions such as in the Netherlands for example, the performance ratio of a PV system in the winter months could reach an average PR of 82.1%, compared to 73.2% in the summer months. 

Based on the reports analysis of more than 600 PV plants in key countries around the world, PV system performance and annual yield variability can primarily be explained by irradiation and climate zone differences.

The study showed that a PV system could reach its optimum performance level when the ambient temperature was actually below –5 ºC and would gradually decline to 65%(PR) when the temperature exceeded +25 ºC.

The report also attempted to delve into PV system poor performance and failure analysis, noting that PV inverter issues as well as junction box issues did play a part in system failures but was statistically very small. 

However, PV system performance crucially required adequate monitoring that would also support better forward grid forecasting.