Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells

Abstract

5.1 It is the intent of these procedures to provide recognized methods for testing and reporting the electrical performance of photovoltaic modules and arrays. 5.2 The test results may be used for comparison of different modules or arrays among a group of similar items that might be encountered in testing a group of modules or arrays from a single source. They also may be used to compare diverse designs, such as products from different manufacturers. Repeated measurements of the same module or array may be used for the study of changes in device performance. 5.3 Measurements may be made over a range of test conditions. The measurement data are numerically translated from the test conditions to standard RC, to nominal operating conditions, or to optional user-specified reporting conditions. Recommended RC are defined in Table 1. 5.3.1 If the test conditions are such that the device temperature is within ±2 °C of the RC temperature and the total irradiance is within ±5 % of the RC irradiance, the numerical translation consists of a correction to the measured device current based on the total irradiance during the I-V measurement. 5.3.2 If the provision in 5.3.1 is not met, performance at RC is obtained from four separate I-V measurements at temperature and irradiance conditions that bracket the desired RC using a bilinear interpolation method.4 5.3.2.1 There are a variety of methods that may be used to bracket the temperature and irradiance. One method involves cooling the module under test below the reference temperature and making repeated measurements of the I-V characteristics as the module warms up. The irradiance of pulsed light sources may be adjusted by using neutral density mesh filters of varying transmittance. If the distance between the simulator and the test plane can be varied, then this adjustment can be used to change the irradiance. In natural sunlight, the irradiance will change with the time of day or if the solar incidence angle is adjusted. 5.4 These test methods are based on two requirements: 5.4.1 First, the reference cell (or module, see 1.1.1 and 4.3.4) is selected so that its spectral response is considered to be close to the module or array to be tested. 5.4.2 Second, the spectral response of a representative cell and the spectral distribution of the irradiance source must be known. The calibration constant of the reference cell is then corrected to account for the difference between the actual and the reference spectral irradiance distributions using the spectral mismatch parameter, which is defined in Test Method E973. 5.5 Terrestrial reference cells are calibrated with respect to a reference spectral irradiance distribution, for example, Tables G173. 5.6 A reference cell made and calibrated as described in 4.3 will indicate the total irradiance incident on a module or array whose spectral response is close to that of the reference cell. 5.7 With the performance data determined in accordance with these test methods, it becomes possible to predict module or array performance from measurements under any test light source in terms of any reference spectral irradiance distribution. 5.8 The reference conditions of 5.3.1 must be met if the measured I-V curve exhibits “kinks” or multiple inflection points.