Comparison of used PV degradation of different PV technologies using I-V characteristics

In Thailand PV power plants have been commercially installed since early 2010, as part of a government incentive program called ADDER (which add to the normal tariff for a 10-year support duration). The FiT (Feed-in Tariff) scheme, offering a fixed cost over a 25-year support duration, was introduced as the market grew rapidly. Regular testing of PV modules from there power plants began around the fifth year of operation and continues thereafter. These PV modules were tested under standard conditions at an accredited ISO 17025 laboratory, providing performance data at Standard Test Condition (STC) according to IEC 61215. This study aims to simplify the degradation of electrical parameters such as power, current, and voltage in relation to the year of operation, which is useful for classifying unknown sets of PV module testing results. There is a set of performance data at STC for crystalline silicon and some of thin film PV modules, as detailed in Table 1.

The relationship between current and voltage determines the power output. Annual sets of PV modules tested at STC show the characteristics of their performance and degradation rate. From the current-voltage characteristic, we found that the maximum power current (Imp) is strongly related to the maximum power (Pmax) as shown in Figure 1. This relationship is useful for identifying data sets, as it varies with the years of operation. The results of the study will provide valuable for comparing the degradation of power output in different PV technologies.

Table 1: List of PV module technologies, year of operation, and locations.