Experimental study of mismatch and shading effects in the I–V characteristic of a photovoltaic module

A conventional photovoltaic module has been prepared with the purpose of accessing its cells either individually or associated. Measurements of every cell and of the whole module have been performed in direct and reverse bias, with the objective of documenting the scattering in cell parameters, working point of the cells and shading effects. Several shading profiles have been tested, and the influence of the reverse characteristic of the shaded cell in module output is stressed.     

Low light conditions modelling for building integrated photovoltaic (BIPV) systems

The low irradiance efficiency of photovoltaic modules is important to the optimization of BIPV systems. When photovoltaic modules are integrated into a building, architectural design considerations compete with maximizing photovoltaic energy production. As a result, BIPV arrays are often not facing south and are frequently mounted vertically. Under these conditions, a greater portion of the total sunlight striking the array is diffuse or at high angles of incidence. In northern latitudes a significant amount of the total yearly energy is produced at low light levels.A grid-connected array of BIPV modules integrated into the BCIT Technology Centre building in Burnaby, B.C. was used for assessing the accuracy of an energy performance model developed for BIPV systems. The BIPV system uses AC modules and a computerized data acquisition system for monitoring the performance of modules and inverters. The performance model was developed from analysis of the open circuit voltage, maximum power point voltage and maximum power point current of the individual modules comprising the BIPV array.The algorithm for calculating power output of the photovoltaic array is derived from the ideal diode equation using the single diode model of a photovoltaic cell. An empirically derived parameter modifies the equation. Once the parameters for different module technologies are established, it is possible to compare their annual performance in a BIPV system.     

Artificial neural network modelling and experimental verification of the operating current of mono-crystalline photovoltaic modules

This article presents the artificial neural network modelling of the operating current of a 120 Wp of mono-crystalline photovoltaic module. As an alternative method to analytical modelling approaches, this study uses the advantages of neural networks such as no required knowledge of internal system parameters, less computational effort and a compact solution for multivariable problems. Generalised regression neural network model is used in the present article to predict the operating current of the photovoltaic module. To show its merit, the current predicted from the artificial neural network modelling is compared to that from the analytical model. The five-parameter analytical model is drawn from the equivalent electrical circuit that includes light-generated current, diode reverse saturation current, and series and shunt resistances. The operating current predicted from both the neural and analytical models are compared to the measured current. Results have shown that the artificial neural network modelling provides a better prediction of the current than the five-parameter analytical model.     

Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer

Here we report on optical modelling of organic photovoltaic devices having a layered geometry, with polyfluorene-copolymer as the active material and C₆₀ as the acceptor. Thin film theory in a matrix formalism enables analysis of the impact of reflection and interference on the optical electric field. The model allows us to predict an optimal C₆₀ thickness where concern has been taken for light being both polychromatic and distributed according to solar irradiation. Fundamental for light–matter interaction is the dielectric function. We have extracted it for two variants of a new polyfluorene copolymer, PFDTBT, from UV via visible to the nearest infrared, using spectroscopic ellipsometry (SE). n is found to be relatively high with a max-value above 2.1. The process of spin coating induces anisotropy in the polymer film.     

Specifying targets of future research in photovoltaic devices containing pyrite (FeS2) by numerical modelling

The performance of pyrite (FeS₂) in photovoltaic devices is forecast for various device structures by means of numerical modelling. The physical model is based on recent investigations of thin-film pyrite layers, allowing a forecast for realistically achievable (non-ideal) material parameters. It is confirmed that, in a feasible form, pyrite possesses electrical properties that are suitable for photovoltaic energy conversion. Based on the simulation results, targets for future work are suggested in order to increase the efficiency of solar cells containing pyrite. The interpretive tools presented here may be applied to other photovoltaic materials as well.     

An equivalent circuit approach to the modelling of the dynamics of dye sensitized solar cells

A model that can be used to interpret the response of a dye-sensitized photo electrode to intensity-modulated light (intensity modulated voltage spectroscopy, IMVS and intensity modulated photo-current spectroscopy, IMPS) is presented. The model is based on an equivalent circuit approach involving a transmission line with both an electrical and an ionic branch. An analytical expression including a term from the passive electrochemical impedance of the network, and a term accounting for the photo generation in the electrode is found. From this model IMVS and IMPS responses as well as iV curves can be calculated and used to optimize the photo electrode with respect to thickness and density. The result is mathematically equivalent to the usual approach for IMVS and IMPS modelling based on diffusion equations describing the transport of electrons in the semiconductor and on charge accumulation in traps, although these assumptions are not included in the transmission line model. The diffusion-like behaviour shows up as a consequence of the topology of the coupling between transport processes rather than as an inherent property of the electron transport itself. In this model electron trapping occurs because of electrostatic interactions between electrons in the semiconductor and ions in the electrolyte.     

Modelling the light absorption in organic photovoltaic devices

Electromagnetic reflection, transmission and absorption properties are basically important for the optical characterization of multilayers used in optoelectronic and photovoltaic devices. They describe the interaction of incident light with the layers of the system. Depending on the thicknesses and optical constants of the individual layers, the interaction of a light source with a multilayer causes distinct distributions of the electric field and energy absorption density. Consequently the optical modelling of an organic bilayer photovoltaic device, in which the incident sunlight must be absorbed in a very narrow region near the active interface, has to take into account the influence of the optical parameters and the thicknesses of the device layers in order to gain optimal energy conversion. We focussed on the electrodynamic behavior of organic photovoltaic bilayer devices with varied layer thicknesses. We found a sensitive response of the maxima of the absorption density inside the solar cell to even fine changes in the thicknesses of the active layers. We also investigated the electrodynamic behavior of a photovoltaic device in dependence on the incident light wavelength. As a new and interesting result, our investigations showed a good correlation between measured photo current and calculated absorption density and no good correlation between measured photo current and calculated square of the electric field.     

A comparative study of approaches to direct methanol fuel cells modelling

Fuel cell modelling has received much attention over the past decade in an attempt to better understand the phenomena occurring within the cell. Mathematical models and simulation are needed as tools for design optimization of fuel cells, stacks and fuel cell power systems.     

Theoretical and experimental analysis of the behaviour of a photovoltaic pumping system

The aim of the paper is to present the influence of the solar radiation variation on the performances of a stand alone photovoltaic pumping system which consists of photovoltaic generator, dc-dc converter, dc-ac inverter, an immersed group motor-pump and a storage tank that serves a similar purpose to battery storage. Hence a theoretical analysis (modelling and control) of the system is needed. Attention has been paid to the command of the power converters using MPPT and variable laws. The MPPT control allows the extraction of the maximal output power delivered by the PV generator. The inverter ensures the PWM control of the asynchronous motor and a sine wave form of output signals. From the obtained simulation results, we will show that the decrease of the solar radiation degrades performances (the global efficiency and the flow rate) of the PV pumping system. The analysis is validated by simulation and experimental results.     

Regional modelling of oil discovery and production

This paper outlines a new method for summarizing the exploratory and production potential of an aggregated geographical region in terms of the past history of exploration and production at the field level. The analytical framework is divided into two stages. First, the discovery analysis describes the physical returns to exploratory drilling (marginal expected field size), which provide additions to the potential reserve base. Subsequently, the production analysis specifies the economic costs of bringing new fields on stream, and also describes the likely production rate from fields of distinct physical characteristics. In both the exploratory stage and the production stage, the negative influence of resource depletion is modelled explicitly. The expected size of successive field discoveries is subject to exponential decay at a rate determined by analysis of past discovery history. In the production stage, production flow declines exponentially from the peak rate as the field is exhausted, Finally, the paper contains new estimates of development cost functions that are sensitive to both economic parameters and the physical characteristics of fields. The cost functions relate total investment expenditure to the size of fields, the rate of extraction, and the productivity of individual wells. The analytical framework is illustrated by application to 37 individual regions around the world.     

Analysis of the operational performance and efficiency characteristic for photovoltaic system in Hong Kong

The applications of photovoltaic (PV) systems have become more widespread in both developed and developing countries. The most critical exercise in designing a PV system is the determination of the optimum size of the solar panel and the battery capacity to meet the load demand with acceptable reliability. The amount of power generated by a PV system strongly depends on the availability of solar insolation at the required location. Also, the efficiency of a PV system is influenced considerably by a number of climatic variables, such as solar irradiance availability and ambient temperature. The technical information is provided for standard test conditions that may never occur in practice. Reliable knowledge of the performance of PV systems under actual operating conditions is essential for correct product selection and accurate performance prediction. This paper investigates the operational performance and efficiency characteristic of a small PV system installed at the City University of Hong Kong. The solar data and the power generated by the PV system are systematically recorded and analysed. The findings provide technical data in different months for designers and engineers to assess and size PV systems.     

Thermo-fluid dynamics modelling of steam electrolysis in fully-assembled tubular high-temperature proton-conducting cells

Electrolysis based on renewable energies offers a promising carbon-free solution for hydrogen generation and storage. The recent developments of proton ceramic electrolysis cells operating at intermediate temperatures bear promise of superior energy efficiency compared to oxide ion conducting electrolytes. Here, a proton ceramic Single Engineering Unit (SEU) design is optimized for steam electrolysis using a computational fluid dynamics (CFD) model implemented in a COMSOL Multiphysics software. The SEU is an all-in-one tubular cell arrangement that constitutes the smallest electrolysis unit and enables efficient, adaptable pressurized hydrogen generation. The parametrical modelling study is conducted for two adiabatic operation scenarios with distinct steam conversion rates and tested for multiple key parameters, namely internal and external chamber pressures and inlet stream temperature. The modelling results show that low steam conversions enable operation at higher current densities and that the thermoneutral voltage for a fixed steam conversion is highly sensitive to the process conditions and operation modes. The increment of the pressure of the generated hydrogen implies a reduced production rate at thermoneutral voltage, although it can be compensated with an enhanced steam pressure or a reduced inlet temperature. Additionally, the introduction of a porous medium as the SEU current collector in the steam chamber enhances heat transport within this chamber. The area specific resistance of the system determines the current density, enforcing an adaption of the area of the electrolyser to satisfy the target hydrogen production and energy efficiency. The resulting proposed SEU design and adapted operational parameters allow effective delivery of pressurized dry hydrogen for a wide range of conditions and applications.     

Sizing and modelling of photovoltaic water pumping system

With the decline in price of the photovoltaics (PVs) their use as a power source for water pumping is the most attractive solution instead of using diesel generators or electric motors driven by a grid system. In this paper, a method to design a PV pumping system is presented and discussed, which is then used to calculate the required size of the PV for an existing farm. Furthermore, the amount of carbon dioxide emissions saved by the use of PV water pumping system instead of using diesel-fuelled generators or electrical motor connected to the grid network is calculated. In addition, an experimental set-up is developed for the PV water pumping system using both DC and AC motors with batteries. The experimental tests are used to validate the developed MATLAB model. This research work demonstrates that using the PV water pumping system is not only improving the living conditions in rural areas but it is also protecting the environment and can be a cost-effective application in remote locations.     

Identification and monitoring of a PEM electrolyser based on dynamical modelling

To improve the efficiency and the safety of hydrogen electrolysis stations, some technological studies are still under investigation both on methods and materials. As methods, control, monitoring and diagnosis algorithms are relevant tools. This work focuses on the dynamical modelling and the monitoring of Proton Exchange Membrane (PEM) electrolyser. Our contribution consists of three parts: to propose a model of an analytical–dynamical PEM electrolyser, dedicated to control and monitoring; to identify the model parameters and to propose adequate monitoring tools. The proposed model is deduced from physical laws and electrochemical equations and consists of a steady-state electric model coupled with a dynamic thermal model. The estimation of the model parameters is achieved using identification and data fitting techniques based on experimental measurements. Taking into account the information given by the proposed analytical model and the experimentation data (temperature T, voltage U and current I) given by a PEM electrolyser, the model parameters are identified. After estimating the dynamical model, model-based diagnosis is used to monitor the PEM electrolyser and to ensure its safety. We illustrate how our algorithm can detect and isolate faults on actuators, on sensors or on electrolyser system.     

Solar radiation modelling for the simulation of photovoltaic systems

The effect of 12 different combinations of diffuse–global correlations and tilted surface radiation models on the accuracy of PV output simulation of a grid-connected photovoltaic (PV) system was studied using statistical methods. A site specific diffuse–global correlation was developed using local insolation data and the performance of this model was compared with those of two other diffuse–global correlations. The impact of diffuse–global correlations on the calculated inclined insolation for four different tilted surface radiation models was investigated on annual, seasonal and monthly basis. The accuracies of predicted 45° inclined plane insolation and PV output were improved when the site specific diffuse–global correlation was used in the main simulation model. The error between measured and predicted inclined insolation was higher in winter than summer. The prediction of PV output was improved by using an isotropic sky tilted surface radiation model instead of the anisotropic models. The accuracy of PV output was also improved when the proposed diffuse–global correlation was used.     

Numerical modelling of trap-assisted tunnelling mechanism in a-Si:H and μc-Si n/p structures and tandem solar cells

The trap-assisted tunnelling theory was developed to describe the tunnelling of charge carriers via bandgap energy levels in structures based on hydrogenated amorphous silicon and microcrystalline silicon. Its implementation into ASPIN numerical simulator is explained. Models that were verified on n/p single junctions were applied in the tunnel recombination junction area of a tandem solar cell. Thus, it is possible to study a multi-layer solar cell without separately simulating any of its components.     

Dynamic modelling and simulation of a photovoltaic refrigeration plant

In this paper, we will present the performances, the simulation responses and the dynamic behaviour of a photovoltaic (PV) refrigeration plant using latent storage. This approach uses a new storage strategy of stand alone PV plants which substitutes the battery storage with thermal, eutectic, latent or a hydraulic storage. The measurements and the evaluation of these less battery storage systems at several climatic conditions and under load disturbances allow us to evaluate the PV system reliability and to compare its performances with classic battery storage systems.     

The iterative contribution and relevance of modelling to UK energy policy

This paper discusses the iterative provision of modelling insights on long-term decarbonisation scenarios for UK energy policy makers. A multi-year model construction process of the UK MARKAL-Macro-hybrid energy-economic model, and four subsequent major policy analyses illustrates the scope of this interaction. The initial set of modelling runs focused on the technical feasibility of long-term 60% carbon dioxide (CO₂) reduction scenarios, the role of key technologies, and the underlying uncertainties. Furthermore subsequent modelling studies were aimed to generate insights on more stringent targets, and on issues and uncertainties that may make targets harder to achieve. Hence, this paper analyses the large number of long-term UK CO₂ reduction scenarios through a clustering approach on target stringency and barriers to implementation. Robust findings and key uncertainties are highlighted, including the critical role of the power sector, trade-offs between resources, sectors, key energy technologies and behavioural responses, and the increasing level and spread of CO₂ marginal prices and GDP impacts. The relevance and use of modelling insights to the UK energy policy process is shown in the continuation of the energy modelling–policy interface. This constitutes both ongoing model development, and nuanced scenario analysis designed to further explore key uncertainties in evolving policy issues.     

Estimation of global radiation using clearness index model for sizing photovoltaic system

A methodology for developing a simple theoretical model for calculating global insolation on a horizontal surface is described in this paper. The input parameters to the model are the latitude of the desired location and the amount of total precipitable water content in the vertical column at that location. Both the parameters are easily measurable with inexpensive instrument such as global positioning system (GPS). The principal idea behind the paper is to have a model that could be used for designing a photovoltaic system quickly and within reasonable accuracy. The model in this paper has been developed using measured data from 12 locations in India covering length and breadth of the country over a period of 9–22 years. The model is validated by calculating theoretical global insolation for five locations, one in north (New Delhi), one in south (Thiruvanandapuram), one in east (Kolkata), one in west (Mumbai) and one in central (Nagpur) part of India and comparing them with the measured insolation values for these five locations. The measured values of all these locations had been considered for developing the model. The model is further validated for a location (Goa) whose measured data is not considered for developing the model, by comparing the calculated and measured values of the insolation. Over the range of latitudes covering most parts of India, the error is within 20% of the measured value. This gives the credibility of the model and the methodology used for developing the model for any region in the world.