Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice

IEA-PVPS Task 13: “Performance and Reliability of Photovoltaic Systems”

The monitoring of single PV modules plays an important role in the demonstration and deeper understanding of technological differences in PV module performance, lifetime and failure mechanisms.

With the growing share and relevance of PV in the market, the number of stakeholders performing outdoor measurements at module level is continuously increasing: test institutes, certification labs, PV module manufacturers, but also non-experts in the field, e.g. distributors, investors or insurance companies are publishing their results in a wide range of media, from scientific to technical journals, from risk assessment reports to purely commercial publications. The comparability of these measurements is, however made difficult by the different testing approaches and missing declarations on measurement uncertainties. This is mainly due to the fact that there is no dedicated standard or recognized guideline published, covering the specific needs of PV module energy yield measurements.

The two main reference documents available today are a best practice guideline for the testing of single modules which was presented by DERLAB (European Distributed Energy Resources Laboratories) in 2012 and the IEC 61724-1 Technical Standard for the monitoring of PV systems, published in 2017. The first one is limited to the definition of some testing requirements, without distinguishing between different testing purposes. It does not consider uncertainty contributions at single measurement level and gives no recommendations of how to reduce them. The second one addresses many of the missing aspects, with details on sensors, equipment accuracy, quality check and performance analysis, but without considering the special requirements of single module monitoring and benchmarking studies.

The current practices for energy yield measurements of individual PV modules applied by major international research institutes and test laboratories are presented in this report. Best practice recommendations and suggestions to improve energy yield measurements are given to the reader.

Performing a survey conducted within the IEA PVPS Task13 consortium, we wanted to assess how module energy yield measurements are performed today and how the uncertainties are calculated and reported to the end-users. Fifteen Task members with experience in PV module monitoring from over 30 test facilities installed all over the world have been interviewed. Many ISO17025 accredited test laboratories, as well as R&D institutes, have been included. The questionnaire covered all aspects, starting from general questions on the scope of testing to the test equipment, procedures, maintenance practice, data analysis and reporting.