Degradation of photovoltaic modules under high voltage stress in the field

Abstract

The degradation in performance for eight photovoltaic (PV) modules stressed at high voltage (HV) is presented. Four types of modules-tandem-junction and triple-junction amorphous thin-film silicon, plus crystalline and polycrystalline silicon modules-were tested, with a pair of each biased at opposite polarities. They were deployed outdoors between 2001 and 2009 with their respective HV leakage currents through the module encapsulation continuously monitored with a data acquisition system, along with air temperature and relative humidity. For the first 5 years, all modules were biased continuously at fixed 600 VDC, day and night. In the last 2 years, the modules were step-bias stressed cyclically up and down in voltage between 10 and 600 VDC, in steps of tens to hundreds of volts. This allowed characterization of leakage current versus voltage under a large range of temperature and moisture conditions, facilitating determination of leakage paths. An analysis of the degradation is presented, along with integrated leakage charge. In HV operation: the bulk silicon modules degraded either insignificantly or at rates of 0.1%/yr higher than modules not biased at HV; for the thinfilm silicon modules, the added loss rates are insignificant for one type, or 0.2%/yr-0.6%/yr larger for the other type.

In-the-field PID related experiences

“…PID recovery capacity has also been tackled in some tests [14], [23], [48] although attempts at predicting the evolution of PID in the field have to date led to inconclusive results. An LC accumulated charge was proposed as PID indicator [49] but it was found not to be directly correlated with the occurrence of PID [50], [51]. Shunt resistance appears to be more correlated with PID [52], [53] but the practical modelling of its progression gave rise to severe difficulties as there is general lack of data on relative humidity across the front glass surface, which is a key parameter of this modelling.…”

Experimental Analysis of the Potential Induced Degradation Effect on Organic Solar Cells

“…design [7,9], which are also called as module-level factors [8,10]. Regarding cell-level factors, the antireflective coating, emitter depth, and type of base doping are three major parameters that also affect PID in the cell level [9,10,11].…”

Diagnostics and testing of photovoltaic devices

“…The samples were stored at temperature 85 °C and biased by 1000 V DC as it is common for PID treatment [3]. The complex impedance parametersthe phase and absolute value -were measured by SOLARTRON Analytical Module in order to detect frequency response of experimental minimodules.…”