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The constant progress of the efficiency values of the multijunction (MJ) solar cells based on III-V semiconductors, used together with photovoltaic concentration (CPV) technologies, means that competitive costs can be achieved generating solar photovoltaic energy, since with concentration a cell's area is reduced, being substituted by optical elements of a lower cost. The present thesis collects a series of contributions at different levels that affect CPV systems. The largest part is dedicated to the impact of solar spectrum on these systems based on MJ cells, specifically to the understanding of that effect on MJ cells and CPV systems. Firstly the spectral matching ratio (SMR) concept is reviewed, an index based on the currents of a set of component cells (isotypes) that is used to estimate which subcell of a MJ cell limits, and its use is extended to MJ cell calibration with the role of spectral index. In particular, through instants filtering using SMR baseline values, prevailing spectral conditions are established with regard to reference spectrum (ASTM AM1.5D G173-03). Based on those component cell currents the so-called equivalent irradiances are defined, with which is possible to estimate the losses due to spectrum (spectral efficiency) when they are compared to the corresponding direct irradiance (DNI). Finally a study about the spectral bias when calibrating is presented, in particular the effect due to the tolerance associated with the SMR filters and the contribution due to spectral mismatch when using component cells of different technology to the MJ cell. The second contribution about spectrum is a study of the spectral classification based on SMR indexes from several locations around the world for several MJ cell technologies: lattice matched based on germanium and dilute nitrides and metamorphic, both upright and inverted. In this way relations can be established among types of locations defined by their geography and climate and spectral clusters useful for MJ cell ad hoc design. An estimation of losses due to spectral variation for each MJ technology for each location is also given. In the last contribution related to spectrum a possibility for SMRs as spectral indexes is looked at closely, previously establishing the minimum number of parameters needed to estimate the uniqueness of solar spectra. It is concluded that a single spectral index is clearly insufficient to establish spectral uniqueness and that three independent indexes are close to the biunivocal spectral identification. Based on this idea the use of SMR to establish correlations among different MJ cell technologies and other devices is suggested. Following on, a review of the factors that affect the energetic production of a CPV plant is given, and how these factors are modeled in the software photovoltaic (PV) tools that add simulation modules for CPV. Particular emphasis is placed on those factors that, influenced by the way PV systems are modeled, cause errors or present a lack of precision when the same approaches are used in CPV and recommendations and used limitations are proposed. All this is applied to an experimental 50 kW CPV plant in the NGCPV European-Japan project and its energy production for two years is compared with the models of integrated power and annual energy forecast. Finally, a hybrid CPV design with lighting is proposed as part of the Spanish project LUZ-CPV, where concentration, in addition to generating photovoltaic electricity, is used to transport sunlight directly for indoor illumination. In principle the hybrid concept allows an efficiency improvement of a CPV system used to illuminate by means of electrical luminary, since the transmission of sunlight is direct without energy transformation. A study about the design limitations has been performed, a full prototype has been developed and both CPV and lighting parts have been characterized. To conclude, several light guide materials have been studied to estimate the viability of the concept. RESUMEN El avance constante de los valores de eficiencia de las celulas solares multiunion (MJ) basadas en semiconductores III-V permite que utilizadas junto con tecnologias de concentracion fotovoltaica (CPV) puedan alcanzarse costes competitivos en la generacion de energia solar fotovoltaica, ya que al concentrar se reduce el area de celula necesaria siendo sustituida por elementos opticos de mucho menor coste. La presente tesis recoge una serie de contribuciones a distintos niveles que afectan a los sistemas CPV. La mayor parte esta dedicada al impacto del espectro solar sobre dichos sistemas basados en celulas MJ, en concreto al entendimiento de dicho efecto sobre celulas MJ y sistemas CPV. Primero se revisa el concepto de spectral matching ratio (SMR), un indice basado en las corrientes de un set de celulas componentes (isotypes) que es utilizado para estimar que subcelula de una celula MJ limita, y se extiende su uso a calibracion de celulas MJ utilizandolo como indice espectral. En concreto, mediante el filtrado de instantes utilizando valores SMR de referencia, se establecen las condiciones espectrales prevalentes con respecto el espectro de referencia (ASTM AM1.5D G173-03). Basandose en las mismas corrientes de las celulas componentes se definen la correspondientes irradiancias equivalentes, con las que se puede estimar la perdida debida al espectro (eficiencia espectral) al comparar con el valor de irradiacion directa (DNI) correspondiente. Finalmente se ha estudiado la aparicion de sesgos en la calibracion espectral, en concreto el efecto de la tolerancia asociada a los filtros SMR y la contribucion por desajuste espectral al utilizar celulas componente de distinta tecnologia que la celula MJ. La segunda contribucion sobre el espectro trata de un estudio sobre la clasificacion espectral basadas en indices SMRs de diversas localidades alrededor del mundo para diversas tecnologias de celula MJ: ajustadas en red basadas en germanio y nitruros y metamorficas tanto rectas como invertidas. De esta forma se establecen relaciones entre tipos de localidades definidas por su geografia y clima y se pueden identificar clusteres espectrales utiles para el diseno ad hoc de celulas MJ. Tambien se estiman las perdidas por variacion espectral asociadas a cada tecnologia MJ para cada localidad. Como ultima contribucion relacionada con el espectro se profundizan las posibilidades de los SMRs como indices espectrales, estableciendo previamente el numero minimo de parametros necesarios para estimar unicidad de los espectros solares. Se concluye que un solo indice espectral es claramente insuficiente para establecer unicidad espectral y que tres indices independientes se acercan bastante a una identificacion espectral biunivoca. Basado en ello se sugiere utilizar los SMR para establecer correlaciones entre diferentes tecnologias de celula MJ y otros dispositivos. A continuacion se da una revision de los factores que afectan a la produccion energetica de una planta CPV y como se modelan en las herramientas software de fotovoltaica (PV) que incorporan componentes para simulacion CPV. Se hace especial hincapie en aquellos factores que, influenciados por la forma de modelar sistemas PV, ocasionan errores o falta precision cuando se utilizan las mismas aproximaciones sobre sistemas CPV y se proponen recomendaciones y limitaciones de uso. Todo ello es aplicado a una planta CPV experimental de 50 kW dentro del proyecto europeo con Japon NGCPV y se compara el modelado con la produccion durante dos anos, a nivel de potencia y de energia anual estimada. Por ultimo, se propone un diseno CPV hibrido con iluminacion bajo el proyecto nacional espanol LUZ-CPV en el que se hace uso de la concentracion ademas de para la generacion fotovoltaica de electricidad, para el transporte directo de luz solar con el fin de iluminar interiores. El concepto hibrido permite en principio mejorar la eficiencia de un sistema CPV que se utilice para iluminar mediante una luminaria electrica, ya que la transmision de luz es directa sin necesidad de transformacion energetica. Se ha hecho un estudio para ver las limitaciones de diseno, se ha desarrollado un prototipo completo y se ha caracterizado tanto la parte CPV como la de iluminacion. Para finalizar se han estudiado diversos materiales utilizados como guia optica para estimar la viabilidad del concepto.

Contributions to characterization, modeling and design of concentrator photovoltaic systems