Design, development, and analysis of a densely packed 500x concentrating photovoltaic cell assembly on insulated metal substrate

The paper presents a novel densely packed assembly for high concentrating photovoltaic applications, designed to fit 125x primary and 4x secondary reflective optics. This assembly can accommodate 144 multijunction cells and is one of the most populated modules presented so far. Based on the thermal simulation results, an aluminum-based insulated metal substrate has been used as baseplate; this technology is commonly exploited for Light Emitting Diode applications, due to its optimal thermal management. The original outline of the conductive copper layer has been developed to minimize Joule losses by reducing the number of interconnections among the cells in series. Oversized Schottky diodes have been employed for bypassing purposes. The whole design fits the IPC-2221 requirements. The plate has been manufactured using standard electronic processes and then characterized through an indoor test and the results are here presented and commented on. The assembly achieves a fill factor above 80% and an efficiency of 29.4% at 500x, less than 2% lower than that of a single cell commercial receiver. The novel design of the conductive pattern is conceived to decrease the power losses and the deployment of an insulated metal substrate represents an improvement towards the awaited cost-cutting for high concentrating photovoltaic technologies

Proceedings of the Flat-Plate Solar Array Project Research Forum on the Design of Flat-Plate Photovoltaic Arrays for Central Stations

The Flat Plate Solar Array Project, focuses on advancing technologies relevant to the design and construction of megawatt level central station systems. Photovoltaic modules and arrays for flat plate central station or other large scale electric power production facilities require the establishment of a technical base that resolves design issues and results in practical and cost effective configurations. Design, qualification and maintenance issues related to central station arrays derived from the engineering and operating experiences of early applications and parallel laboratory reserch activities are investigated. Technical issues are examined from the viewpoint of the utility engineer, architect/engineer and laboratory researcher. Topics on optimum source circuit designs, module insulation design for high system voltages, array safety, structural interface design, measurements, and array operation and maintenance are discussed

Investigation of reliability attributes and accelerated stress factors on terrestrial solar cells

Major effort during this reporting period was devoted to two tasks: improvement of the electrical measurement instrumentation through the design and construction of a microcomputer controlled short interval tester, and better understanding of second quadrant behavior by developing a mathematical model relating cell temperature to electrical characteristics. In addition, some preliminary work is reported on an investigation into color changes observed after stressing

Development and study of a dense array Concentration PhotoVoltaic (CPV) system

In the past several years there has been a growing commercial interest in Concentration PhotoVoltaics (CPV) thanks to its promise of low cost electrical power generation. While the technology of CPV using point-focus Fresnel-like optical elements is reaching maturity, the systems based on dense array receivers still need further scientific progress. This thesis explores the field of CPV applied to a parabolic concentrator prototype and to a dense array receiver made of multijunction solar cells. The solar concentrator, completely designed and built at the University of Trento, is characterized, in order to get the illumination distribution on the PV receiver. The non-uniformity in incident flux results in a current mismatch among cells and strongly impacts the system performance. In order to solve this issue, we have proposed a new type of electrical connection by fitting each cell of the array with an individual DC-DC converter. This method is shown to increase the power transfer efficiency with respect to classical series connection, at least for the tested illumination levels and unbalances. The other main problem with dense array systems is the reliability of the PV receiver, with special attention to the high thermal flux to be dissipated. Several types of water-cooled receivers have been built, with different material configurations that were previously studied with 3D thermal modeling. In particular the building of a multi-cell receiver has required the design of the insulation/interconnection between the cells, the tuning of the cell soldering and the realization of front contact connections

Modeling and Analysis of the Operation of PV Power Generators Under Varying Atmospheric Conditions

Photovoltaic (PV) technology permits us to harness and transform solar radiation into electricity. However, PV power generators are still a minor share in the global power generation capacity. One of the main reasons for it is that PV systems are greatly dependent on the atmospheric conditions affecting their operation. Furthermore, series connection of PV cells is prone to power losses when the electrical characteristics of the cells are dissimilar or the cells operate under non-uniform operating conditions. Especially during changing atmospheric conditions, the operation and control of PV generators is complicated and there is a demand for improvement since today’s inverters do not reach their best performance. In this thesis, a state of the art inclusive thermal and electric simulation model of PV generators is proposed and validated with data measured at the Tampere University of Technology (TUT) solar PV power station research plant. The dynamic thermal and electric behaviors of the PV modules are first modelled separately theoretically based on previous authors’ work. Subsequently, these models are further improved by analyzing module temperature measurements and the electric behavior of the PV modules operating under varying meteorological conditions. All the relevant climatic and site specific parameters, heat transfer mechanisms and parasitic resistive effects are considered without major simplifications to obtain the highest possible accuracy. Finally, the separate thermal and electric models are integrated and the result is a comprehensive simulation model that predicts the thermal and electric performance of PV generators operating under varying atmospheric conditions. This simulation model is intended, among other things, to assist in the inverter design and development of maximum power point (MPP) tracking algorithms, especially to improve their efficiency and operation under non-ideal and fast changing environmental conditions. Partial shading affects the electrical characteristics of PV generators, causing them to operate away from their MPP and thus complicating the task to reach the maximum power production. This task is normally carried out by the power electronic converters interfacing the PV generators. Furthermore, partial shading conditions generally cause mismatch losses too. In this thesis, a method to generate a spatial irradiance map from a set of irradiance measurements is proposed and utilized to analyze the effect of moving clouds on the mismatch losses on several PV generator configurations and layouts. The mismatch losses are studied for several sizes of generators in which both series and parallel connection of PV modules are considered. The results indicate that the mismatch power losses caused by non-uniform operating conditions due to moving clouds can be reduced by locating PV modules of the generator as close to each other as possible. Furthermore, parallel connection of PV modules should be favored with respect to series connection

Modeling photovoltaic panels under variable internal and environmental conditions with non-constant load

This thesis focuses on the modeling and simulation of photovoltaic electric energy conversion systems, that considering different internal and environmental parameters, important for the forecast of the electric energy production. For the cell or panel modeling, the single diode five-parameter model is used. The internal parameters considered are the photocurrent, the cell temperature, the ideality factor, the series resistance, the shunt resistance and the saturation current; and on the other hand the external parameters considered are solar irradiance, ambient temperature and wind speed. New contributions are presented in the context of the modeling and simulation of the error function that identifies the more and less sensitive internal parameters of the cell model and the sensitivity of the external parameters. In the context of obtaining the experimental results, a monocrystalline silicon photovoltaic panel is used. And a signal generator, data acquisition device, an anemometer, a pyranometer and a sensor for measuring the ambient temperature are used. In the context of internal relation between external parameters, correlation studies are performed in order to show the relationships between them; and the obstacle concept is presented as a generalization of shadow types, namely dust and elements that reduce solar irradiance on the surface of the cell or panel; Modelação de painéis fotovoltaicos sob condições internas e ambientais variáveis com carga não constante Resumo: Esta tese incide sobre o tema da modelação e simulação de sistemas de conversão de energia elétrica fotovoltaica considerando diferentes parâmetros internos e ambientais, importantes para a previsão da produção de energia elétrica. Para a modelação da célula ou do painel é utilizado o modelo de cinco parâmetros de um díodo. Os parâmetros internos considerados são a corrente que atravessa o díodo, a temperatura interna da célula, o fator de idealidade, a resistência série da célula, a resistência paralela da célula e a corrente de saturação; os parâmetros externos considerados são a irradiância solar, a temperatura ambiente e a velocidade do vento. São apresentadas novas contribuições no contexto da modelação e simulação da função de erro que identifica os parâmetros internos mais e menos sensíveis do modelo da célula e a sensibilidade dos parâmetros externos. No contexto para a obtenção dos resultados experimentais foram utilizadas células e um painel fotovoltaico de silício monocristalino respetivamente, um gerador de sinais, dispositivos aquisição de dados, um anemómetro, um piranómetro e um sensor para medir a temperatura ambiente. Em ambos contextos, são realizados estudos de correlação entre os parâmetros externos no sentido de mostrar as relações entre eles; e é apresentado o conceito de obstáculo como uma generalização dos tipos de sombras, nomeadamente a poeira e elementos que reduzem a irradiância solar na superfície da célula ou do painel

Wide-bandgap semiconductor based power converters for renewable energy systems

The demand for low carbon economy and limited fossil resources for energy generation drives the research on renewable energy sources and the key technology for utilisation of renewable energy sources: power electronics. Innovative inverter topologies and emerging WBG semiconductor based devices at 600 V blocking class are the enabling technologies for more efficient, reliable and accessible photovoltaic based electricity generation. This thesis is concerned with the impact of WBG semiconductor based power devices on residential scale PV inverter topologies in terms of efficiency, volume reduction and reliability. The static and dynamic characterisation of the Si and WBG based devices are carried out, gate drive requirements are assessed and experimental performance comparison in a single phase inverter is discussed under wide range of operating conditions. The optimisation of GaN HEMT based single phase inverter is conducted in terms of converter efficiency, switching frequency and converter volume. The long term mission-profile based analysis of GaN and Si based devices is conducted and impact of WBG devices under low and high switching frequency conditions in terms of power loss and thermal loading are presented. Finally, a novel five-level hybrid inverter topology based on WBG devices is proposed, simulated and experimentally verified for higher power applications

Space Photovoltaic Research and Technology, 1988. High Efficiency, Space Environment, and Array Technology

The 9th Space Photovoltaic Research and Technology conference was held at the NASA Lewis Research Center from April 19 to 21, 1988. The papers and workshop summaries report remarkable progress on a wide variety of approaches in space photovoltaics, for both near and far term applications. Among the former is the recently developed high efficiency GaAs/Ge cell, which formed the focus of a workshop discussion on heteroepitaxial cells. Still aimed at the long term, but with a significant payoff in a new mission capability, are InP cells, with their potentially dramatic improvement in radiation resistance. Approaches to near term, array specific powers exceeding 130 W/kg are also reported, and advanced concentrator panel technology with the potential to achieve over 250 W/sq m is beginning to take shape