Advances in integration of photovoltaic power and energy production in practical systems

This thesis presents advances in integration of photovoltaic (PV) power and energy in practical systems, such as existing power plants in buildings or directly integrated in the public electrical grid. It starts by providing an analyze of the current state of PV power and some of its limitations. The work done in this thesis begins by providing a model to compute mutual shading in large PV plants, and after provides a study of the integration of a PV plant in a biogas power plant. The remainder sections focus on the work done for project PVCROPS, which consisted on the construction and operation of two prototypes composed of a PV system and a novel battery connected to a building and to the public electrical grid. These prototypes were then used to test energy management strategies and validate the suitability of the two advanced batteries (a lithium-ion battery and a vanadium redox ow battery) for households (BIPV) and PV plants. This thesis is divided in 7 chapters: Chapter 1 provides an introduction to explain and develop the main research questions studied for this thesis; Chapter 2 presents the development of a ray-tracing model to compute shading in large PV elds (with or without trackers); Chapter 3 shows the simulation of hybridizing a biogas plant with a PV plant, using biogas as energy storage; Chapters 4 and 5 present the construction, programming, and initial operation of both prototypes (Chapter 4), EMS testing oriented to BIPV systems (Chapter 5). Finally, Chapters 6 provides some future lines of investigation that can follow this thesis, and Chapter 7 shows a synopsis of the main conclusions of this work; Resumo: Avanços na integracão de potência fotovoltaica e producão de energia em sistemas práticos Esta tese apresenta avanços na integração de potência e energia fotovoltaica (PV) em sistemas práticos, tais como centrais existentes ou a rede eléctrica pública. Come ça por analisar o estado corrente do fotovoltaico no mundo e aborda algumas das suas limitações. O trabalho feito para esta tese de doutoramento começou pelo desenvolvimento de um modelo para calcular os sombreamentos que ocorrem em grandes campos fotovoltaicos, e depois apresenta um estudo sobre a integração um sistema fotovoltaico em uma central eléctrica a bióg as. As ultimas secções da tese focam-se no trabalho feito para o projecto PVCROPS, que consistiu na construção e operação de dois demonstratores, cada um formado por um sistema fotovoltaico e bateria conectados a um edíficio e a rede eléctrica pública. Estes protótipos foram posteriormente utilizados para testar estratégias de gestão de energia (EMS) e para validar a operação de duas baterias avançadas (bateria de Iões de Li tio e bateria de Fluxo Redox de Van adio) e a sua utiliza ção para habitações e centrais PV. A tese está dividida em 7 capitulos: O capitulo 1 apresenta uma introdução para explicar e desenvolver as principais questões que foram investigadas nesta tese; O capitulo 2 mostra o desenvolvimento de um modelo baseado em traçados de raios para calcular sombreamentos mútuos em grandes centrais PV (com e sem seguidores); O capitulo 3 mostra a simulação da hibridização de uma central electrica a biogas com uma central PV, e utilizando o biógas como armazenamento de energia. Os capitulos 4 e 5 apresentam a construção, programação e operação inicial dos dois demonstradores (Capitúlo 4), o teste de EMS orientadas para sistemas PV em habitações (Capítulo 5). Finalmente, o capítulo 6 sugere algumas futuras linhas de investigação que poderão seguir esta tese, e o Capítulo 7 faz uma sinopse das principais conclusões deste trabalho.

Ravines in Angola. Causes and restraint methods

The Earth we know today was not always so. Over millions of years have undergone significant ch an g e s brought about by numerous geological phenomena aimed at your balance, some internal order, creating new geological formations and other external order smoothing formations previously created. From t h e tectonic standpoint, Angola is located in a relatively stable area which gives it a certain p ri v i l e g e w h e n compared with some Asian countries or even Americans where quite often occur earthquakes and volcanic eruptions. However, the same cannot be said in relation to the occurrence of an external geodynamics phenomena, such as the ravines, which in recent years has taken shape in many provinces, especially due to anthropogenic activity, giving rise to geological hazards, increasing the risk of damage in buildings and others infrastructures, losses direct or indirect in economic activities and loss of human lives. We understand that the reducing of these risks starts, in particular, by their identification, for later take preventive measures. This work is the result of some research work carried out by the authors through erosion courses of s o i l and stabilization of soils subject to erosion phenomena, carried out by Engineering Laboratory of Angola (LEA). For the realization of this work, we resorted to cartographic data query, literature, listening to s o m e o f the provincial representatives and local residents, as well as the observation in lo co o f s o m e af f e ct ed areas. The results allow us to infer that the main provinces affected by ravine phenomenon are located in Central and Northern highlands, as well as in the eastern region, and more recently in Cuando-Cub an go province. Not ruling out, however, other regions, such as in Luanda and Cabinda [1]. Relatively the causes, we can say that the ravines in Angola are primarily due to the combination of three natural factors: climate, topography and type of soil [2]. When we add the anthropogenic activit y , namely the execution of construction works, the drainage system obstructio n, exploration of m i n e ral s, agriculture and fires, it is verified an increasing of the phenomenon, often requiring immedi at e act i o n . These interventions can be done through structural or engineering measures and by the stabilization measures on the degraded soil cover [3]. We present an example of stabilization measures throu g h t h e deployment of a local vegetation called Pennisetum purpureum. It is expected that the results may contribute to a better understanding of the causes of the ravine phenomenon in Angola and that the adopted stabilization method can be adapted in other affected provinces in order to prevent and making the contention of the ravines.

Abstraction and use of groundwater for heating buildings in a hard rock environment

In order to turn more efficient the heating of class rooms in the lower floor of the old building of the University of Évora (a XVI century building), five drillings were organised inside the area of the university (Figure 1). The purpose was to use the temperature differential of groundwater in relation to air, by means of a heat exchanger, and use this process to heat the rooms using less energy, turning the heating process less expensive. The wells were drilled in fractured rocks (gneisses), and the purpose was to locate them at least around 100 m one from each other, whilst trying to have a hydraulic connection in-between. From the five initial wells, four were successful in terms of productivity, but just two of them (RA1 and RA2) proved to be hydraulically connected. The wells were equipped with screens for all their drilled depth (100 m), except for the first six meters and some two or three pipes of six meters each, to allow space for the installation for submersible pumps. The length of the installed screens guarantees a good efficiency of the system. In the wells with no connection, the heating system can work using each single well for abstraction and injection, but the process is much less efficient than in the cases where interaction between wells is possible through the rock’s fracture network.