Temperature Coefficient Of Maximum Power Research Articles

Snail trails on PV modules in Brazil’s tropical climate: Detection, chemical Properties, bubble formation, and performance effects

This case study examines relationships among crystalline-Si cell microcracks, the formation of snail trails, the chemical processes involved, and resulting power loss of the modules under operating conditions in the tropical climate of Brazil. Snail-trail discolorations are imaged by ultraviolet fluorescence and are correlated with the electrical losses of the underlying microcracks by electroluminescence. Complementary microanalytical-techniques are used to compare the chemistry/composition of the encapsulant, contacts, and cell surface regions above and separated from snail trails. The formation of Ag-nanoparticles that react with oxygen, CO2, moisture, and the organic encapsulant result in the formation Ag-compounds (i.e., Ag2CO3. AgO2) accounting for the snail-trail discoloration. Bubble formation along the Ag-fingers are reported. Additionally, evolution of bubble trails along the microcracks is observed for the first time, and the resulting chemical interactions are identified. The processes are discussed in terms of the materials, condition of the backsheets, and local environmental and climate interactions. The modules are shown to exhibit additional power-loss at the higher operating temperatures (>50–60 °C) beyond that expected from the maximum-power temperature coefficient. This is attributed to the opening of the microcracks, with Pmax returning to near its original value upon cooling with observed to healing of the microcrack regions.

Investigation of temperature coefficients of PV modules through field measured data

Varying broadband irradiance and temperature are generally known as the major factors influencing the performance of PV modules, but studies have also shown the substantial impact of spectral variations. In this work, a simple and efficient method to calculate the temperature coefficient using long term data is demonstrated. Temperature coefficients of PV modules are estimated from long term performance data following IEC 60891 standard with additional spectral correction, and are compared against the datasheet values. Significant improvement of correlation coefficient from −0.89 to −0.97 is observed during the regression for maximum power temperature coefficient of two poly-crystalline modules, after spectral correction by spectral factor (SF). Also, the standard deviation of yearly estimated values of these coefficients reduced from 5–7 % to 1–2 %. In another setup involving spectral measurements and various PV technologies, the annual mean of 1.62 eV for average photon energy in 350–1700 nm range, suggests a general blue shift of the spectrum. Higher averages than reference values of useful fraction (UF) for c-Si, CIGS and HIT technologies also validate the blue shift of spectrum. Results show SF produces maximum power temperature coefficients closer to the datasheet values compared to UF, suggesting better applicability of SF as an index for spectral correction. The coefficient values were found closer to STC values and the results from Mann and Kendall test, employed to detect any underlying monotonic trend in the development of temperature coefficients over eight years, showed no increasing or decreasing trend and hence no degradation of temperature coefficients for the long-term exposed PV modules.

Potential-induced degradation: Recombination behavior, temperature coefficients and mismatch losses in crystalline silicon photovoltaic power plant

In recent years, potential-induced degradation (PID) has gained considerable attention due to the significant negative impact on output power of photovoltaic power plant. In this paper, the recombination behavior of PID-affected solar modules dismounted from the photovoltaic power plant was investigated by the two-diode model of photovoltaic module. The mechanism of PID shunting, which is caused by sodium decorated stacking faults across n+-p junction, was further verified by analyzing changes in the quasi-neutral region and the space-charge region for PID-affected p-type crystalline silicon solar modules. It was found that the depletion region recombination increases with the extent of PID. The electroluminescence images also revealed that there exist strong ohmic shunts for PID-affected modules. Then the fundamental temperature coefficients of PID-affected solar modules were investigated. It was found that the increased depletion region recombination leads to a larger temperature coefficient of maximum power for PID-affected solar modules. The result was also verified by the thermography images of PID-affected modules. Finally, the relative mismatch losses (RML) of PID-affected module strings were analyzed. The results revealed that the RML of PID-affected module strings increase as the root-mean-square error (RMSE) of current at maximum power point progressed for the first time.

Selection Map for PV Module Installation Based on Shading Tolerability and Temperature Coefficient

Power generation from photovoltaic (PV) modules suffers from heat losses that are a function of the temperature coefficient of maximum power ( γ ) of the PV module. Another loss mechanism is shading, where the power output of the module and ultimately the system can be severely compromised. Various approaches such as passive, active, or smart bypasses and module level power electronics have been employed to minimize the effects of shading on a PV module. So far, the performance of a PV module under shading had only been addressed vaguely and was generally described qualitatively. Therefore, a probability-based parameter called shading tolerability (ST) was recently developed to quantify the behavior of PV modules under all kinds of shade. However, the observations pertaining to ST were only carried out at 25 °C ambient temperature. Hence, this paper aims to: 1) investigate whether ST is an innate property of a PV module by formulating a correlation between ST and ambient temperature, 2) classify various PV technologies based on ST and γ, and 3) develop a PV module selection map. Theoretical result shows that thermal features of a PV module (nominal operational cell temperature and γ) can influence the PV module ST by 12.25%. Also, an analytical limit is derived for ST variation with respect to ambient temperature change $(\Delta \text{ST}/ \Delta T_{a})$ . The proposed selection map, which is similar to the Ragone plot for energy-storing devices, is validated using the data of 27 PV systems installed in the Netherlands. The map can be used for optimal selection of PV modules for the design of PV systems simply by knowing the specifications of the module along with the meteorological conditions of the installation location.

Energy performance of different silicon photovoltaic technologies under hot and harsh climate

This paper presents a performance comparison study performed on four photovoltaic modules. Three silicon technologies are concerned: one monocrystalline module, two polycrystalline modules and one module of tandem structure (amorphous/microcrystalline) also known as micromorph module. The modules I–V data and meteorological data have been measured during one year using an outdoor monitoring test facility named “IV bench”. This set up is installed at Ouagadougou (Latitude 12.45° North, Longitude 1.56° West) in Sudano Sahelian climate. The actual maximum power, the average performance ratios, the series resistances and the maximum power temperature coefficient of tested modules are determined from the outdoor measurements and used for comparison study. The power of all the modules has been stabilized in outdoor conditions before the performance analysis. The results show that the micromorph module presents the best performance on the selected site, with an average performance ratio of 92%. The monocrystalline and polycrystalline modules from the same manufacturer, have both an average performance ratio of 84%. The second polycrystalline module from another manufacturer, strangely presents the lowest average performance ratio (80%) due to both its large series resistance and the high maximum power temperature coefficient in operating conditions.

Commercial photovoltaic system design for Cardiff City Hall

The rooftops of Cardiff City Hall were surveyed to establish potential areas for commercial-scale photovoltaic (PV) system design. The orientation and tilt angles of suitable unshaded roof areas were measured for accurate PV system simulation. The performance of two PV technologies, polycrystalline silicon (p-Si) and heterojunction with intrinsic thin layers (HIT) was investigated. From the analysis of simulation, experimental, environmental and economic data, HIT was found to be the best-performing PV technology for system installation. Superior performance of HIT under diffuse sunlight conditions, typical of the UK climate, was demonstrated. Additionally, the maximum power temperature coefficient, verified during experimental work, was lower than the p-Si alternative (−0·28 against −0·50%/°C). Electricity demand data for City Hall were analysed and 8·1% of the annual electricity demand (solar fraction) could be supplied by an 88 kWp HIT PV system. The HIT PV system modelled would significantly improve the energy performance of Cardiff City Hall, avoiding >40 000 kg carbon dioxide emissions annually. The levelised cost of energy from one array (B, £0·11/kWh) was less than the current day tariff rate for grid import (£0·1173). The economic and environmental benefits of well-designed high-efficiency PV systems in the UK at commercial scale are also demonstrated.