Results of the 3rd Modelling Round Robin within the European Project „PERFORMANCE”– Comparison of Module Energy Rating Methods

Abstract

During the four years of the PERFORMANCE project enormous contributions to pre-normative research related to photovoltaic modules and systems have been achieved. The contributions ranged from instantaneous device characterisation and system measurements to their life-time performance prediction and assessment. This paper presents the results of the 3rd and final modelling Round Robin (RR3) for PV module energy prediction. It describes the inter-comparison of various energy prediction methods with a direct link to the currently discussed IEC61853 energy rating standard. The previous modelling round robin RR2 showed that further improvements by implementing spectral and angle of incidence effects is very difficult to achieve without increasing the reliability and availability of the main input parameters as well as the implementation of better models for diffuse irradiance. Independent of the type of technology, none of the models were able to significantly improve the energy prediction with respect to the basic approach of using only in-plane irradiance and back of module temperature, which reached ±3% on an annual basis and 6% on a monthly basis. An improvement was only achieved for clear sky days. The translation from horizontal to in-plane irradiance led to the largest errors, this was mainly due to the high uncertainty in diffuse irradiance measurements and/or its translation to the tilted plane. The main objectives of the last round robin RR3 were to improve some of these critical points and to propose a simple device comparator. Eight different energy prediction methods and three module technologies (c-Si, CdTe and a-Si) were investigated. Similar to the procedure in the previous round robins, all models are validated by comparing calculated performance with real performance data for the modules installed at different test sites across Europe. One of the main points which will be discussed in this paper is the accuracy in modelling the energy output starting from a short measurement campaign, where the measurements were either performed outdoors or indoor with a solar simulator. The differences in energy prediction errors due to the use of indoor and/or outdoor data is analysed in more detail along with the accuracy achieved for cloudy days. Furthermore, the proposed improvements in the modelling of energy output for amorphous silicon modules by using new methods are discussed. The study included also the implementation of the IEC 61853 energy rating algorithm with the use of standard literature values for the modelling of reflection losses and simulated solar spectrum for the spectral effect.