DETERMINATION OF INTERNAL SERIES RESISTANCE OF PV DEVICES: REPEATABILITY AND UNCERTAINTY

Abstract

ABSTRACT: Accuracy and reliability in the determination of series resistance RS of PV devices is an important issue, not only in industrial production environment, because of the parasitic and power consuming nature of this intrinsic parameter, but also in measurement and test laboratories, due to its influence during the translation of measured IV curves to reporting conditions. This work follows standard IEC 60891 ed.2 (2009) for the determination of the internal series resistance and focuses on the repeatability of the result and its uncertainty. The latter is studied in particular considering a possible variation of device temperature during the I-V measurements for the RS determination. An analytical expression is derived for quantifying the additional apparent series resistance ∆RS due to temperature variation. Experimental results confirm the derived expression. Although the standard IEC 60891 ed.2 (2009) states that a constant device temperature is required during the I-V curve measurements, it sets the limits for stability within ±2°C. Here it is found that this would lead to a deviation ∆RS, which is comparable to RS itself. However, if the temperature variation is limited to ±0.1°C, which is achievable on pulsed solar simulators, the deviation of RS is limited to ±5%. The repeatability of RS was found to be typically better than 5%. Conservatively, simply adding the two components, the overall combined expanded uncertainty (k=2) for the determination of RS is found to be ±10%. It is recommended to revise IEC 60891 ed.2 concerning the device temperature during determination of RS.JRC.F.7-Renewables and Energy Efficienc