PEAK-POWER AND INTERNAL SERIES RESISTANCE MEASUREMENT UNDER NATURAL AMBIENT CONDITIONS

Quality inspection of PV-modules includes measurement of peak-power Ppk and internal series resistance R s. Peak- power is defined as maximum power under standard test conditions (STC). As the peak-power can decrease due to degradation effects, a continuous quality inspection has to be realized on-site under natural ambient conditions. Losses in the PV-modules can be described by an internal series resistance R s. An increasing R s shows internal losses as well as degrading contacts. A measuring method is presented, which can measure under natural ambient conditions and directly display the results peak-power P pk and internal series resistance R s. I-V-characteristics measured under ambient conditions can be corrected concerning temperature and irradiation according to IEC 60891. The description of the characteristic by the "effective solar cell characteristic" makes it possible to explicitely carry out the calculations for P pk. IEC 60891 also describes a method for the evaluation of the internal series resistance Rs. A graphic method is used in order to determin certain points in the I-V-characteristic, which serve as input-values for the calculation of the series resistance. The accuracy of this graphic method is limited by the accuracy of the graphically determi ned points. Using the method of the "effective solar cell characteristic" it is possible to explicitely calculate the demanded poin ts of the I-V-characteristic, thus beeing capable of explicit calculation of the series resistance R s. The method of the "effective solar cell characteristic" is presented as well as some significant results concerning P pk- and Rs-measurement under natural ambient conditions.