Jai Prakash Singh

Potential-induced degradation in photovoltaic modules: a critical review

Potential-induced degradation (PID) has received considerable attention in recent years due to its detrimental impact on photovoltaic (PV) module performance under field conditions. Both crystalline silicon (c-Si) and thin-film PV modules are susceptible to PID. While extensive studies have already been conducted in this area, the understanding of the PID phenomena is still incomplete and it remains a major problem in the PV industry. Herein, a critical review of the available literature is given to serve as a one-stop source for understanding the current status of PID research. This paper also aims to provide an overview of future research paths to address PID-related issues. This paper consists of three parts. In the first part, the modelling of leakage current paths in the module package is discussed. The PID mechanisms in both c-Si and thin-film PV modules are also comprehensively reviewed. The second part summarizes various test methods to evaluate PV modules for PID. The last part focuses on studies related to PID in the omnipresent p-type c-Si PV modules. The dependence of temperature, humidity and voltage on the progression of PID is examined. Preventive measures against PID at the cell, module and system levels are illustrated. Moreover, PID recovery in standard p-type c-Si PV modules is also studied. Most of the findings from p-type c-Si PV modules are also applicable to other PV module technologies.

On the optical design of thin film amorphous silicon solar cells

We have developed an optical analysis method to design the structure of multi-layer thin film solar cells. The optimised thickness of the individual layers in any single as well as tandem type thin film a-Si:H solar cells ban be obtained. By minimising the reflectance using an optimal anti-reflection coating layer and selecting a suitable rear contact material, a significant increase in the photon collection efficiency at long wavelength can be achieved. The effect of the variation in the thickness of different layers on the performance characteristics of a cell is discussed. The calculated results and analyses show that the present theoretical approach can be used directly to design any thin film solar cell with an optimised structure for a desired high conversion efficiency.

Assessment of combined TCO/metal rear contact for thin film amorphous silicon solar cells

An optical admittance method is applied to investigate the effect of light absorption enhancement on glass/TCO/p-i-n/TCO/metal type thin film a-Si:H solar cells. The results reveal that a combined TCO/metal as a rear contact for a p-i-n type thin film a-Si:H solar cell can further increase the integrated absorbance in the active layer of the device. The optimal structure of such a device with the top and rear TCO thin film coatings is discussed.

Optical properties of very fine Al particles: Quantum size effect

The strong attenuation of the parallel‐band absorption observed in very fine Al particles at 0.85 μm is interpreted in terms of a quantum mechanical size effect. Applying a quantum theoretical model, the dielectric constant for fine particles is calculated, and the effective dielectric constants for aggregated films are obtained classically from the Maxwell–Garnett theory. Calculated results of transmittance for Al blacks in the spectral range from 0.35 to 1.0 μm are found in very good agreement with experimental results.

Comparison of Glass/Glass and Glass/Backsheet PV Modules Using Bifacial Silicon Solar Cells

Bifacial solar cells can be encapsulated in modules with either a glass/glass or a glass/backsheet structure. A glass/backsheet structure provides additional module current under standard test conditions (STC), due to the backsheet scattering effects, whereas a glass/glass structure has the potential to generate additional energy under outdoor conditions. In this study, we quantify the current contributions due to various mechanisms in both module structures under STC. The current contributions due to different mechanisms are calculated by measuring the reflectance and transmittance of mini-modules with both structures, together with a MATLAB-based simulation. Our results show that under STC, glass/backsheet modules provide approximately 2.2% more power, as compared with glass/glass modules using the same bifacial solar cells with a standard cell gap of 2.0 mm. Using module optimization, we demonstrate that the maximum possible cost reduction benefit in

Optical modelling of a single-junction p-i-n type and tandem structure amorphous silicon solar cells with perfect current matching

/WP of glass/backsheet modules over glass/glass modules under STC is limited to 3.3%. Due to the potential outdoor energy yield advantages of glass/glass modules reported in the literature, we recommend a glass/glass module structure for bifacial solar cells. Furthermore, in order to compensate for the lower performance of glass/glass modules under STC, we propose a methodology to measure and fairly rate bifacial glass/glass photovoltaic (PV) modules.

In-Situ Characterization of Potential-Induced Degradation in Crystalline Silicon Photovoltaic Modules Through Dark I–V Measurements

Abstract Using the admittance analysis method, the optimal design of a single junction a-Si : H solar cell is suggested and its photovoltaic parameters are calculated. The technique is then extended to design a tandem structure of two cells stacked one on the top of the other and connected in series. The top cell is considered of a-Si : H and bottom of a-SiGe : H and the condition of current matching is applied to determine the tandems optimal design. The efficiency of the single-junction cell with the optimal design is predicted to be 13.1% and that of the tandem cell with the perfect current matching is 20.8%. The results of our calculations are discussed in the light of the recent experimental results.

Optimizing Gallium Arsenide multiple quantum wells as high-performance photovoltaic devices

A temperature correction methodology for in-situ darkI-V(DIV) characterization of conventional p-type crystalline silicon photovoltaic (PV) modules undergoing potential-induced degradation (PID) is proposed. We observe that the DIV-derived module power temperature coefficient (γ_dark) varies as a function of the extent of PID. To investigate the relationship between γ_dark and DIV-derived module power (P_dark (T_s), measured in situ and at the stress temperature) two parameters are defined: change in the DIV-derived module temperature coefficient (Δγ_dark) and DIV-derived module power degradation at the PID stress temperature (ΔP_dark (T_s)). It is determined that there is a linear relationship between Δγ_dark and ΔP_dark (T_s). Based on this finding, we can easily determine the module γdark at various stages of PID by monitoring P_dark (T_s) in situ. We then further develop a mathematical model to translate P_dark (T_s) to that at 25 °C (Pdark (25 °C)), which is correlated with the module power measured at the standard testing conditions (PST C). Our experiments demonstrate that, for various degrees of PID, the temperature correction methodology offers a relative accuracy of ±3% for predicting PST C. Furthermore, it reduces the root-mean-square error (RMSE) by around 70%, compared with the PSTC estimation without the temperature correction.

Transport of excitation energy at impurities distributed randomly in a three-dimensional crystal lattice

We examine the possibility of using gallium arsenide (GaAs) quantum wells, which have significantly high absorption coefficient for photon energies near the energy band gap, as high-performance solar cells. Using a semi-empirical model of the absorption spectrum, we determine the critical well widths at which the efficiencies of solar cells based on the GaAs/AlxGa1−xAs quantum well structure can be optimized.

On the thermodynamic efficiency of solar energy converters: Solar cells

Abstract Using the continuous time random walks, the decay probability of an excitation at an impurity site is calculated numerically employing a general fractal distribution function in a three-dimensional disordered lattice. Results agree well with the previously calculated theoretical probabilities and also with experimental results.