BIPV, Energy Performance, Energy Rating, Experimental Methods, Facade
Summary / Abstract:
The international standard IEC 61853-1 contains two procedures for the evaluation of PV module output (Pmp) over a range of irradiances (GPOA) and module temperatures (Tmod): a procedure for indoor labs and a procedure for outdoor measurements (we neglect the option of using a tracker, which is quite challenging for BIPV-systems). The data from the IEA PVPS Task 15 (Enabling Framework for the Acceleration of Building Integrated Photovoltaics, BIPV) roundrobin has been used for an in-depth analysis of the differences between the indoor and outdoor determined Pmp-matrix. Moreover, the variety in the matrices of the eight individual test sites in various parts of the world is investigated. The approach is based on specific filtering of the outdoor data and color plot the relevant parameters in 2D matrices (of GPOA and Tmod) including the statistics of all data points that are present in each bin of that matrix. Filtering on Angle Of Incidence (AOI) and distance to center of the bin has been applied to make the comparison as precise as possible. Even after this filtering it was found impossible to decrease the standard deviation (stdev) of all points within a bin to a value lower than 5% as requested from the standard. A more realistic criterium of 10% stdev is proposed to use. The systematic fluctuations within each bin are caused by environmental factors that were not controlled or measured in our round-robin. These factors are, in random order: non-uniformity of (i) GPOA and (ii) Tmod within the module area, (iii) thermal dynamics between the Tmod sensor on the back of the PV-module and the actual Tcell that determines Pmp, (iv) soiling, (v) spectral effects. In conclusion, following the indoor and outdoor procedure of the IEC 61853-1 does not give the same Pmp-matrix for a given (BI)PV-module type. Significant differences are observed and analyzed. These results show that it might be very challenging to use the outdoor procedure without tracker for the purpose of energy rating. Leading to the recommendation to use the indoor procedure for energy rating of PV-modules and use the outdoor procedure for a well-defined quantification of energy losses caused by the aforementioned fluctuating environmental factors always present in realistic (BI)PV-systems.