Investigation of Efficiency for PID-Affected Solar Module at Nonstandard Test Conditions

Potential-induced degradation (PID) causes a sharp decrease in the efficiency and shunt resistance of the solar module. In this paper, PID-affected modules were studied detailedly under non-standard light conditions for the first time. The trend of efficiency degradation was obtained by measuring irradiance-efficiency ƞ and the ΔI-Δƞ. The result shows that the efficiency (I-ƞ) of PID-affected module reduced by 1.28% which is rather higher than the 0.2% of PID-free module when the light intensity changes from 400 W/m2 to 200 W/m2. This means that efficiency of PID-affected module decreases more seriously in low light conditions.

I. Introduction

The photovoltaic energy will provide a substantial contribution to future energy demand as one of the promising clean and renewable energy resources. The efficiency of the PV modules is extremely critical for the total power output of the system, the cost effectiveness of the PV(photovoltaics) system and the commercial success of photovoltaic energy [1]–[4]. In grid-connected photovoltaic systems the individual modules are usually connected serially to strings so as to increase system voltage. Partial solar cells incorporated into PV modules in this architecture can be exposed to a voltage bias of several hundreds of volts. A degradation mechanism named as potential-induced degradation (PID) significantly leads to remarkable efficiency losses [5]. These losses are so significant that they can not be ignored and have fatal impacts on the long-term system performance [6]–[7]. PID of silicon solar cells is mainly characterized by a significant reduction of the parallel resistance which causes a drop of the efficiency output [8]–[15]. In this paper, the thermography imaging of the PID-affected modules was achieved in the field, and the electrical properties of PID affected solar module dismounted from power plant were measured by using solar simulator (PASAN Sunsim 3C) in the laboratory. We focus on the PID-affected module's efficiency , and the relative change of the efficiency at non-standard insolation conditions. The degradation regularity of efficiency were presented by and the curves characteristic. The PID-free module's etticiency increases almost at the rate of 0.2% per 200 W/m² at non-standard insolation less than 1000 W/m². However, PID-affected module's efficiency is more sensitive to the weak light intensity less than 400 W/m². The lower the light intensity is, the faster the efficiency decreases. The maximum degradation of is about 1.28% which is rather higher than the 0.2% of PID-free module. Besides, the efficiency loss of the last module with PID in module string is up to about 8% at the light intensity of 200 W/m2, and the yield losses of per string affected by PID is approximately up to 45%. The important and profound efficiency regularity of PID-affected modules at non-standard insolation has been detected. Table I The voc of solar modules

Irradiance
200	41.949	41.948 r	41.949	41.947	41.945	41.949	41.948	41.949	41.792
400	43.378	43.376	43.377	43.376	43.374	43.376	43.377	43.378	43.232
600	43.567	43.565	43.566	43.564	43.565	43.568	43.565	43.567	43.456
800	44.882	44.881	44.882	44.884	44.883	44.881	44.883	44.882	44.532
1000	45.261	45.262	45.263	45.263	45.261	45.262	45.261	45.261	45.095

Table II The voc of solar modules

Irradiance
200	41.298	40.902	34.263	32.021	31.927	30.148	29.254	25.582
400	43.099	43.066	38.687	37.465	36.158	33.747	33.487	28.223
600	43.126	43.098	39.156	38.321	37.465	35.564	34.256	30.121
800	44.421	44.411	42.213	41.692	39.654	38.565	36.557	32.545
1000	45.088	45.083	43.555	42.645	40.671	39.125	37.288	33.409