• Energy Research

This paper presents a new methodology to extract the unknown parameters of a single-diode photovoltaic (PV) cell model. The first contribution of this paper is the development and implementation of a new version of the wind-driven optimization algorithm, called an adaptive wind-driven optimization (AWDO) algorithm. The advantages of the AWDO algorithm are: 1) accurate extraction of the global values of the optimized PV parameters in changing weather conditions, which is achieved by building solutions from random operations; and 2) capability of handling the given complex multi-modal and multi-dimensional optimization problems. The second contribution is the identification of a generalization model to generalize the extracted parameters of a single-diode PV cell model. That provides an ability of the proposed methodology to work with any I–V characteristic curve of PV cells and at any weather condition on a 15-min basis. To validate the proposed methodology, it has been tested for 1307 I–V characteristic curves of a PV module at various weather conditions on a 15-min basis. Additionally, its accuracy and computational efficiency are verified and compared with five well-known existing extraction methods: Villalva's model, particle swarm optimization, biogeography-based optimization, Gang's model, and bacterial foraging optimization by both simulation and outdoor measurements. The results show that the AWDO algorithm can provide the extracted five parameters with an acceptable range of accuracy and faster than the aforementioned models. Therefore, the proposed methodology (AWDO based on Chenlo's model) can be confidently recommended as a reliable, feasible, valuable, and fast optimization algorithm for parameter extraction of a single-diode PV cell model.

AbstractThe recent rise in power conversion efficiencies reported for perovskite solar cells has been a remarkable development in photovoltaics research. It is now pressing that the technology transitions from a research phenomenon to a real‐world deployable device: this will require both robust methods for efficiency measurement, and accurate models for performance variation at different conditions. However, the generally slow response of perovskite solar cells to changes in voltage bias and irradiance, and the susceptibility of these cells to degradation, presents significant challenges. In this paper, we investigate current and voltage stabilisation of planar CH3NH3PbI3 perovskite solar cells and observe remarkably large variations in stabilisation time depending on exposure history. To address this, we demonstrate a dynamic approach that continues device pre‐conditioning until pre‐determined stability criteria are met. This approach is then employed to obtain measurements of short‐circuit current and open‐circuit voltage temperature coefficients under quasi‐steady‐state conditions for perovskite devices and a control monocrystalline silicon cell. The obtained open‐circuit voltage temperature coefficient for the perovskite is −2700 ppm/°C, which interestingly, is similar to typically reported values for crystalline silicon devices. It is shown that the implemented approach can successfully differentiate between transient responses to the onset of illumination and true temperature related changes. We also find new manifestations of the complex transient processes that occur in perovskite devices. These observations highlight the importance of sophisticated characterisation approaches for correct characterisation of the performance of perovskite solar cells. Copyright © 2016 John Wiley & Sons, Ltd.

Accurate characterization and reporting of organic photovoltaic (OPV) device performance reniains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using "suitcase sample" approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner. (C) 2014 Elsevier B.V. All rights reserved.

Energy transfer has been identified as an important process in ternary organic solar cells. Here, we develop kinetic Monte Carlo (KMC) models to assess the impact of energy transfer in ternary and binary bulk heterojunction systems. We used fluorescence and absorption spectroscopy to determine the energy disorder and Förster radii for poly(3-hexylthiophene-2,5-diyl), [6,6]-phenyl-C61-butyric acid methyl ester, 4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (DIBSq), and poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-dihydrodithieno[3,2-c:3',2'-h][1,5]naphthyridine-5,10-dione). Heterogeneous energy transfer is found to be crucial in the exciton dissociation process of both binary and ternary organic semiconductor systems. Circumstances favoring energy transfer across interfaces allow relaxation of the electronic energy level requirements, meaning that a cascade structure is not required for efficient ternary organic solar cells. We explain how energy transfer can be exploited to eliminate additional energy losses in ternary bulk heterojunction solar cells, thus increasing their open-circuit voltage without loss in short-circuit current. In particular, we show that it is important that the DIBSq is located at the electron donor-acceptor interface; otherwise charge carriers will be trapped in the DIBSq domain or excitons in the DIBSq domains will not be able to dissociate efficiently at an interface. KMC modeling shows that only small amounts of DIBSq (<5% by weight) are needed to achieve substantial performance improvements due to long-range energy transfer.

Abstract In this paper, an analysis of three-dimensional transient thermal transfer is presented to evaluate the performance of a photovoltaic thermal module with an optimize structural design, incorporating direct use of an aluminum collector as the substrate. The effect of cross-sectional geometries and ratios of size and spacing was considered to optimize the performance of a photovoltaic-thermal (PVT) module. The temperature, velocity and pressure distributions were demonstrated in a steady state model using a finite element method. Simulation results indicated the temperature of the PVT module was increased by the solar irradiation incident with the panel, yet overall decreased by an increased flow velocity. In this study, we examine seven types of media used as the medium to cool the PVT module, where water was preferred, due to its higher specific heat capacity. Further, for multiple interconnected PVT modules, connecting method in parallel and series resulted in pressure drop for the PVT module. In addition, the simulations were compared to experimental data providing validation of the estimated operating temperature in agreement with simulation results, and the outcomes will provide an indication for preferred assembly of PVT modules for application in building integration and future product design.

Abstract Methods for cooling photovoltaic (PV) modules to increase their output have been proposed several times in the literature. Most of these reports describe the increase in power output achieved, but they rarely comment on the economic cost-benefit proposition. Where the economics have been considered, this has been based on measurements for the authors’ specific PV system at a specific site. This means the economics are not easily interpreted for other systems at other sites. We derive a theoretical formulation for quantifying the economic value of artificial cooling of PV modules. The formulation is not specific to any particular method of cooling. It takes as input the rate of heat removal that a cooling method can provide (in Wm–2 or Wm–2K−1) and determines the economic value of this cooling rate, based on variables including local solar conditions, capital cost of the system, system ventilation, plus the temperature coefficient and efficiency of the modules. We find that the economic value of cooling PV depends strongly on the system design and local conditions, with favourable circumstances leading to a viable cost of potentially over $40/m2, however unfavourable circumstances are many times less attractive at less than $1/m2. The equations presented can be used to optimise the design of a cooling feature that is applied to a PV module or system, provided the above parameters of the cooling feature and PV system are established.

AbstractImproving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.