Control of the STC power in PV modules' supplies for utility scale plants

Abstract

This article presents a specific procedure to control the standard test conditions (STC) power in photovoltaic (PV) modules. It also shows the results of its application on a supply of approximately 700 000 multicrystalline p‐type silicon BSF technology PV modules made by a worldwide known manufacturer (Tier‐1, Q4 2015). First, during the manufacturing process, the analysis of the STC power measurements of the whole supply carried out by the modules' manufacturer is included, where the quality of these measurements was evaluated through a comparative contrast study in an independent laboratory on a sample of 4000 modules. In addition, the light‐induced degradation (LID) on 180 modules and the resistance to the potential induced degradation (PID) in a sample of 125 modules were characterized and critically analyzed. Secondly, during operation phase, the analysis of the STC power after the first 2 years of operation of the modules in desert conditions was also included. These measurements were carried out on a sample of 2000 modules making use of an accredited mobile laboratory. The overall results showed the effectiveness of the implementation of the aforementioned procedure, which is based on the use of a set of reference modules (primary standards) with common calibration origin. It proved to be an effective way of reducing uncertainties all along the quality control process. The susceptibility to PID, as observed on the PID test (chamber method) specified in IEC TS 62804, was practically negligible, and the average LID degradation after 20 kWh/m2 of exposition to the sun was 1.5%. Finally, the degradation rate in the second year of operation was 0.32% with respect to the initial degradation occurred during the whole first year.

Experimental observations in mismatch losses in monofacial and bifacial PV generators

“…They are low and tend to decrease as the module mass production progresses. For example, σP MPP PMPP was found to be about 2-3% in modules manufactured around 1990 11 and about 0.5% in modules manufactured around 2015 16 Actual mismatch loss in situ and in operating arrays can be greater due to non-uniformity T C -differences between the modules of the same array may reach over 10 C in standard PV generators 17,18 ; the relationship between field performance and measured performance under simulated light that can make the actual variability greater than that deduced from the flash-reports; and the nonuniformity of illumination, especially in the case of bifacial generators because of the incident irradiance on its rear side, is usually nonuniform. This has been the object of recent studies 19,20 which concluded that the MML resulting from this non-uniformity is usually less than 0.3% in practical PV systems.…”

“…Statistics on the distribution of I-V characteristics of a set of commercial modules under Standard Test Conditions, STC, have been available for many years, and the relationship between the MML and this information has been studied by several authors with the main objective of addressing whether the performance of the array can be improved by pre-sorting the modules or cells. [9][10][11][12][13][14][15][16] That was a relevant question years ago when modules were typically delivered to the market with MPP power under Standard Test Conditions, P Ã MPP , at ±10% around the specified nominal value. However, commercial modules are now classified in such a way that this range has been drastically reduced.…”

Dispersion of operating voltage and temperature in PV generators: influence in mismatch power losses and uncertainty in outdoor PV module characterisation

“…Statistics on the distribution of I-V characteristics of a set of commercial modules under Standard Test Conditions, STC, have been available for many years, and the relationship between the 𝑀𝑀𝐿 and this information has been studied by several authors with the main objective of addressing whether the performance of the array can be improved by pre-sorting the modules or cells [16], [17], [59], [77]- [81].…”

“…ratio between the corresponding standard deviation and the mean value for voltage, current and power, respectively), are low and tend to decrease as the module mass production progresses. For example, 𝐶𝑉 𝑃 M was found to be about 2-3% in modules manufactured around 1990 [16], and about 0.5% in modules manufactured around 2015 [17] using multicrystalline Si BSF (Back Surface Field) technology, and it is certainly still lower at present with increased production and monocrystalline Si PERC (Passivated Emitter and Rear Cell) technology.…”

“…On the other hand, the contractual acceptance/rejection criteria in the STC (Standard Test Conditions) power became stricter, seeking to reduce their uncertainties below 1% [17].…”