New software tool to characterize photovoltaic modules from commercial equipment

A software platform has been developed in order to unify the different measurements obtained from different manufacturers in the photovoltaic system laboratory of the University of Malaga, Spain. These measurements include the current-voltage curve of PV modules and several meteorological parameters such as global and direct irradiance, temperature and spectral distribution of solar irradiance. The measurements are performed in an automated way by a stand-alone application that is able to communicate with a pair of multimeters and a bipolar power supply that are controlled in order to obtain the current–voltage pairs. In addition, several magnitudes, that can be configured by the user, such as irradiance, module temperature or wind speed, are incorporated to register the conditions of each measurement. Moreover, it is possible to attach to each curve the spectral distribution of the solar radiation at each moment. Independently of the source of the information, all these measurements are stored in a uniform relational database. These data can be accessed through a public web site that can generate several graphics from the data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Junta de Andalucía. Proyecto de Excelencia P11-RNM-711

Characterization and modeling of a hybrid electric vehicle lithium-ion battery pack at low temperatures

Although lithium-ion batteries have penetrated hybrid electric vehicles (HEVs) and pure electric vehicles (EVs), they suffer from significant power capability losses and reduced energy at low temperatures. To evaluate those losses and to make an efficient design, good models are required for system simulation. Subzero battery operation involves nonclassical thermal behavior. Consequently, simple electrical models are not sufficient to predict bad performance or damage to systems involving batteries at subzero temperatures. This paper presents the development of an electrical and thermal model of an HEV lithium-ion battery pack. This model has been developed with MATLAB/Simulink to investigate the output characteristics of lithium-ion batteries over the selected operating range of currents and battery capacities. In addition, a thermal modeling method has been developed for this model so that it can predict the battery core and crust temperature by including the effect of internal resistance. First, various discharge tests on one cell are carried out, and then, cell's parameters and thermal characteristics are obtained. The single-cell model proposed is shown to be accurate by analyzing the simulation data and test results. Next, real working conditions tests are performed, and simulation calculations on one cell are presented. In the end, the simulation results of a battery pack under HEV driving cycle conditions show that the characteristics of the proposed model allow a good comparison with data from an actual lithium-ion battery pack used in an HEV. © 2015 IEEE

Photovoltaic self-consumption heating system: analytical model, experimental results and autonomy prospects

Mención Internacional en el título de doctorIn the European Union, buildings are responsible for 40% of energy consumption and 36% of CO₂ emissions, which contribute significantly to anthropogenic climate change. Since heating represents the major portion of energy consumption in buildings in Spain, renewable heating systems emerge as an alternative to mitigate this problem. This thesis proposes a heating system in which the PV production is self-consumed by a heat pump. For this purpose, a photovoltaic off-grid system that feeds an air-water heat pump to heat a small building through radiant loor has been designed and built. The building, despite the aim of being independent, incudes connection to the grid, so the heat pump supply can be switched between the photovoltaic microgrid and the conventional grid. The photovoltaic array, with a total area of 15.7m² and useful area of 14m², is composed by 12 modules, nominal power of 180W each. Heat pump's nominal heating power is 6kW, which is in fine with building's maximum thermal load. To size properly this type of photovoltaic system, it is necessary to go beyond peak sun hours term commonly used by installers and to simulate realistically photovoltaic production over time. The method known as five-parameter model, details the working curve of a module for a given cell temperature. In this thesis, production has been addressed from a physical point of view, emphasizing the influence of solar cells' temperature on their efficiency. A heat transfer model has been developed, which allows to determine accurately cell temperature under changing meteorological conditions, and then to calculate the photovoltaic production in each moment, basing on technical specifications commonly provided by the modules' manufacturers. This dissertation includes the experimental validation of both cell temperature and photovoltaic production models. The efficiency of the used modules, according to their total area, is 13.73% at 25°C, 12.08% at 50°C and 10.76% at 70°C. The proposed method is easily adaptable to any type of photovoltaic module, once its material composition is known, and its output can be simulated for any tilt angle and location, for where meteorological data are available. Depending on obtained working temperatures, the use of hybrid photovoltaic/thermal modules can be considered. The photovoltaic production model was simulated for the heating period from 4/12/2012 to 30/04/2013, predicting an achievable production of 1265.8kWh and an average cell temperature of 21.3°C, which reaches an average daily maximum value of 47.5°C. The intercepted solar energy during that period was 8869.4kWh, so the efficiency of the array according to its useful area would be 14.3%, instead of the nominal value of 15.4%. The photovoltaic heating system was experimentally tested during the same heating period. The array produced 820.8kWh of electricity. The seasonal photovoltaic efficiency was 9.26%. The achieved production was significantly lower than the achievable one, according to the simulation. The heat pump was fed with 723.9kWh of electricity, 501.4kWh of which carne from photovoltaic source: useful efficiency of the system 5.7%. Several factors caused that efficiency, such as electrical losses in diverse conversions, control system's limitations, storage system's capacity and fit of the production to the demand. The ammount of heat supplied to the radiant floor was 2321.9kWh. The seasonal COP was 3.2 and system's global efficiency was 18.2%. The system was isolated from the grid at 69.3%. Greenhouse gases emissions saved were 170.5kgco₂ comparing to feeding the theat pump with conventional electricity (for an emission factor of 0,34kgco₂ /kWh); 835.9 kgco₂ comparing to supplying the same heat ammount through a gas-oil C boiler; 573.6 kgco₂ comparing to a natural gas boiler. On the other hand, refrigerant leaks were equivalent to 132.1 kgco₂.Actualmente, en la Unión Europea los edificios demandan un 40% del consumo total de energía y son responsables del 36% de emisiones de gases de efecto invernadero, contribuyendo significativamente al calentamiento global antrópogénico. Dado que la calefacción supone la principal porción del consumo energético en los edificios en España, los sistemas de calefacción renovable surgen como una alternativa para mitigar dicha problemática. Esta tesis plantea un sistema de calefacción fotovoltaica en el que la producción eléctrica es auto-consumida por una bomba de calor. Para ello se ha diseñado y construido un sistema fotovoltaico sin inyección a red para alimentar una bomba de calor aire-agua que calienta un pequeño edificio mediante suelo radiante. El edificio, tendente a la autonomía, incluye conexión a red, por lo que el suministro a la bomba de calor puede permutarse entre la micro-red fotovoltaica y la red convencional. El campo fotovoltaico, con un área total de 15,7m² y útil de 14m² , está compuesto de 12 paneles, de 180W de potencia nominal cada uno. La potencia térmica nominal de la bomba de calor es de 6kW, al igual que la carga térmica máxima del edificio. Para dimensionar adecuadamente un sistema fotovoltaico de estas características es necesario simular realísticamente la producción fotovoltaica a lo largo del tiempo. En esta tesis, se ha abordado la producción desde un punto de vista físico, haciendo hincapié en 'la influencia de la temperatura de las celdas solares en su eficiencia. Se ha desarrollado un modelo de transferencia de calor que permite determinar con exactitud la temperatura de celda para condiciones meteorológicas cambiantes y, a partir de ahí, la producción fotovoltaica en cada momento, basándose en especificaciones comunmente suministradas por los fabricantes de módulos. La validación experimental del modelo, tanto para la predicción de la temperatura de celda como para la producción fotovoltaica, es incluida en la presente tesis. La eficiencia de los módulos utilizados, respecto a su área total, es de 13.73% a 25°C, 12.08% a 50°C y 10.76% a 70°C. El método planteado es fácilmente adaptable a cualquier tipo de módulo fotovoltaico a partir de los materiales que lo componen, y su producción simulable para cualquier ángulo de inclinación y localización, para la que se disponga de datos meteorológicos. Dependiendo de las temperaturas de trabajo obtenidas, la utilización de paneles híbridos fotovoltaicos/térmicos puede ser planteada. En concreto, el modelo de producción fotovoltaico fue simulado para el periodo de calefacción entre el 4/12/2012 y el 30/04/2013, prediciendo una producción fotovoltaica alcanzable de 1.265,8kWh y una temperatura media de trabajo de celda de 21,3°C, que alcanza una máxima diaria media de 47,5°C. La energía solar interceptada durante ese periodo fue de 8.869,4kWh, por lo que la eficiencia del campo considerando su área útil sería del 14,3%, frente al 15,4% nominal. El sistema de calefacción fotovoltaica fue estudiado experimentalmente durante el mismo periodo de calefacción. El campo produjo 820,8kWh de electricidad, por lo que la eficiencia fotovoltaica estacional fue del 9,26%. La producción obtenida fue inferior a la potencialmente alcanzable, de acuerdo con la simulación. La bomba de calor fue alimentada con 723,9kWh de electricidad, de los cuales 501,4kWh provenían de la fuente fotovoltaica: eficiencia útil del sistema del 5,7%. Multiples factores provocaron dicha eficiencia, tales como las pérdidas eléctricas en las diferentes conversiones, limitaciones del sistema de control, capacidad del sistema de almacenamiento y ajuste de la producción a la demanda. El calor suministrado al suelo radiante fue 2.321,9kWh. El COP estacional de la bomba de 11 calor fue de 3,2 y el rendimiento global del sistema del 18,2%. El sistema operó autónomo de la red a un 69,3%. Las emisiones de gases de efecto invernadero ahorradas fueron de 170,5kgco₂ respecto a alimentar la bomba de calor con electricidad convencional (para un factor de emisión de 0,34kgco₂ /kWh); de 835,9kgco₂ respecto a suministrar el mismo calor a partir de gas-oil C; de 573,6 kgco₂ respecto al uso de gas natural. Por otra parte, las fugas de refrigerante equivalieron a 132,1 kgco₂.Los resultados científicos que se presentan son fruto de la financiación por parte del Ministerio de Ciencia e Innovación del proyecto Diseño, construcción y evaluación experimental de un sistema de refrigeración solar y trigeneración de alta eficiencia para edificios e invernaderos (ENE2010-20650-C02-01) y de la ayuda FPI (BES-2011-050706). El Ministerio de Economía y Competitividad financió la Estancia Breve (EEBB-I-13-06021) en la Universidad de Wisconsin-Madison.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: Francisco Javier Rey Martínez.- Secretario: María Carmen Venegas Bernal.- Vocal: Rafael Antonio Salgado Mangua

Energy delivery of solar farms with reference to shading

This study has been undertaken to research the impact of shading on a large scale solar PV site at 56° latitude north, this is the first site in the UK at this latitude, consisting of 2500 solar panels across a 5 acres. As solar altitude decreases obstacles and blockages become more of a hindrance and careful planning is required to ensure the amount of shading on the panel surface is kept to a minimum. The impacts of shading on the Edinburgh College Solar Meadow, from obstacles along the Southern and Eastern edges have been investigated.The accuracy and applicability of existing methods of solar resource modelling and solar photovoltaic (PV) module performance are investigated in the case of the ground array installation. The principal derived quantities consist of slope irradiation, cell temperature and cell efficiency. Experimental data was collected on site through both automated and manual measurements for comparison with the calculated quantities for both triangulation and quality assurance. The impact of shading has been analysed and the effect on energy delivery captured throughout the year. The research undertook detailed modelling in order to compare and evaluate the data obtained with further comparisons made between a number of modelling tools and other forms of output associated with the solar farm directly.The site was expected to generate 560,000 kWh across the year with no impact from shading, based on the installers assumptions. Results indicate that the models used to compare and contrast slope irradiation, cell temperature and cell efficiency are accurate and within the expected range as per manufacturer specifications. The results also show that shading impacts the energy generation with a significant reduction in the winter months with respect to the available energy at the site by as much as 50%. Being the first study of its kind, at high latitude in the UK, to show the importance of accurate shade modelling at higher latitudes the findings show greater consideration is required at concept stages when taking account of solar obstacles. Shading has reduced the overall output, of this particular array, by 136,859 kWh across the year studied