Determining the optimal standard test condition correction procedure for high‐throughput field I–V measurements of photovoltaic modules

Abstract

AbstractThe field‐measured current–voltage (I–V) curves of photovoltaic (PV) modules need to be corrected to Standard Test Conditions (STC) in order to estimate the degradation rates. STC correction procedures have various attributes such as accuracy, requirement of minimum number and types of I–V curves, required irradiance range, and the type of correction (specific points or entire I–V curve) that determine their optimality for specific applications. This paper presents the investigation of accuracy and constraints of six different STC correction procedures for high‐throughput field I–V measurements through experimental and simulation studies. Following STC correction procedures are considered in this paper: IEC 60891‐Procedure 1, IEC 60891‐Procedure 2, Modified IEC 60891‐Procedure 1, Standard Irradiance and Desired Temperature (SIDT) procedure, Anderson procedure, and Voltage‐Dependent Temperature Coefficient (VDTC) Procedure. Eight different simulation models for predicting the performance of PV modules at arbitrary irradiance and temperature are compared, and the simulation model that yields lowest root mean square error and the most accurate estimation of power temperature coefficient is identified. The simulated I–V curves using this model and the experimentally measured I–V curves on a flash tester at different temperatures and irradiances are provided as an input to all of the STC correction procedures. The average percentage errors in correction of maximum power (Pmax), open‐circuit voltage (Voc), short‐circuit current (Isc), and fill factor (FF) were determined as a function of irradiance and temperature during measurement. Systematic biases introduced during correction by certain procedures were also identified. Based on the error estimation, constraints of various procedures, and requirements of high‐throughput field I–V measurements, the most optimal STC correction procedure was identified. Moreover, the analysis of the root cause of superior performance of this procedure is also presented.