Domestic solar hot water units, if properly designed, are capable of providing all hot water needs in an environmentally friendly and cost-effective way. Despite 50 years of development, commercial technology has not yet achieved substantial market penetration compared to mainstream electric and gas options. Therefore, alternate designs are warranted if they can offer similar or greater performance for a comparable cost to conventional units. This study proved that such alternatives are possible by designing and testing two novel solar hot water systems (SHWS). The first system used compound parabolic collector (CPC) panels to concentrate solar energy and produce steam. The steam moved from a rooftop downward into a heat exchange pipe within a ground level water tank, heating the water, condensing and falling into a receptacle. The operation was entirely passive, since the condensate was pulled up due to the partial vacuum that occurred after system cooling. Efficiencies of up to 40% were obtained. The second system used an air heater panel. Air was circulated in open and closed loop configuration (air recycling) by means of a fan/blower motor and was forced across a compact heat exchanger coupled to a water tank. This produced a natural thermosiphon flow heating the water. Air recycling mode provided higher system efficiencies: 34% vs. 27%. The concurrent development of an analytical model that reasonably predicted heat transfer dynamics of these systems allowed 1) performance optimisation for specific input/starting operating conditions and 2) virtual design improvements. The merit of this model lay in its acceptable accuracy in spite of its simplicity. By optimising for operating conditions and parameter design, both systems are capable of providing over 30 MJ of useful domestic hot water on clear days, which equates roughly to an increase of 35°C in a 200 L water tank. This will satisfy, on average, daily hot water requirements for a 4-person household, particularly in low-latitude regions (eg. Queensland). Preliminary costing for these systems puts them on par with conventional units, with the passive, remotely coupled, low maintenance, CPC SHWS comparable to higher end models. The air heater SHWS, by contrast, was much more economical and easier to build and handle, but at the trade-off cost of 1) the need for an active system, 2) increased maintenance and running costs and 3) the requirement for a temperature control mechanism that would protect the panel body by dumping hot air trapped inside if stagnation were to occur.

Les modules photovoltaïques à concentration (CPV) ont tendance à se miniaturiser. D’une part, la distance focale plus courte des optiques de concentration permet de réduire le besoin en matériaux pour l’assemblage du module ; et d’autre part, le rendement des modules est sensiblement meilleurs que ceux des modules CPV de taille normale. L’étude de chaque élément de la chaine de pertes dans la littérature des micro-concentrateurs a permis de confirmer cette tendance. Cette thèse aborde les problématiques de coût et de rendement à travers la conception optique d’un concentrateur à deux étages de lentilles, sa fabrication puis une étude approfondie de ses performances.La méthode de conception, développée à partir de lois d’optique géométrique et non-imageante, définit le profil des lentilles à λ=589nm en premiers lieux. Ensuite, une simulation par tracé de rayons permet d’optimiser ces lentilles pour l’ensemble du spectre solaire puis d’étudier l’impact de leur désalignement lors de la mise en module. Les limites des déplacements des éléments du module ainsi déterminées conditionnent la précision de sa fabrication. Dans notre cas, l’alignement est réalisé automatiquement par un jeu de repères mécaniques lors du moulage simultané des optiques primaires (POE) et des optiques secondaires (SOE). Contrairement aux procédés habituels, ce procédé de moulage innovant permet d’assembler un module en seulement trois étapes au lieu de cinq.Pour caractériser les micro-concentrateurs réalisés, une méthode de mesure du rapport module à cellule (CTM) est développée. Pour cela, le rendement des cellules est mesuré en simulateur solaire avant et après leur mise en module. Les cellules multi-jonctions mises en œuvre étant sensibles aux variations spectrales et spatiales de l’éclairement, la validation préalable de ces mesures est primordiale. En complément du CTM qui quantifie la somme des pertes introduites lors de la mise en module, d’autres mesures sont développées pour comprendre la chaine de perte plus en détails.Le dispositif étudié au cours de cette thèse utilise des cellules triple-jonction de 0,6 x 0,6mm² avec une concentration de 1000X et atteint un rendement de 29%. Le CTM est de 70% et l’analyse de la chaine de perte montre que le procédé inventé n’impacte pas ou peu les performances du module. De plus, la détermination de la chaine de perte montre que les pertes par réflexion et par absorption sont prédominantes, au même titre que les pertes dues à la diffusion des lentilles ainsi que les pertes dues aux non-uniformités d’éclairement sur la cellule. / The actual trend of CPV is the micro-scaling of modules. A bibliographic study shows that shorter focal length of optics implies less material consumption in manufacturing and an enhanced efficiency of the modules. In this thesis, a double stage refractive micro-concentrator is designed, manufactured and characterized. First, the optical design of the concentrator is based on non-imaging technics. Thus, the profile of the lenses is generated for a single wavelength. Then, a ray tracing simulator is used to optimize the lens profile for the overall solar spectrum and study the concentrator element misalignment effect on the performances.Secondly, a three steps self-assembly process is developed instead of the usual five steps one. Both POE and SOE lenses of our device are molded simultaneously and a mechanical guidance system in the mold ensures the alignment of the micro-concentrator elements (POE, SOE and Cell).Finally, the performances measurements of the manufactured modules are managed in solar simulators in which the lightening condition are previously studied and validated. Comparing the bare cells efficiency with the module efficiency, the cell-to-module ratio (CTM) represents the overall losses in the module. Further experiments are managed to quantify each loss of the module. The manufactured and characterized micro-concentrator is a 1000X concentrating ratio with 0.6 x 0.6mm² triple junction cells. It efficiency is 29% with a 70% CTM. Finally, the loss chain study reveals that the three steps self-assembly process is reliable.