Sviluppo di un modulo daylighting/fotovoltaico ad alta concentrazione basato su fibre ottiche

In recent years, solar energy has attracted worldwide scientific and technological interests as a promising alternative to traditional fossil fuels. Due to their easy installation, high dependability, and absence of fuel cost, photovoltaic systems are now assuming a predominant role for the electric supply of commercial and residential buildings. The aim of the proposed research is to improve the traditional design of high-concentration photovoltaic devices and extend their use for the direct illumination of the interior space of buildings. To this end, we developed a proof-of-concept hybrid module which uses optical fibres to guide 2000x concentrated sunlight from the primary optics to an array of InGaAs/InGaP/Ge multi-junction cells installed in a sheltered place. The first stage of the research dealt with the simulation of the optical properties of the original HCPV system and the evaluation of a number of different optics used to couple the mirror to the optical fibres. The results of our analysis suggested that best performing optics is a fibre bundle which guarantees an effective collection of the sunlight beam, a high mechanical flexibility, and a relatively low cost. The second phase of the investigation was devoted to the study of optical properties of different fibres when exposed to concentrated light. The resistance tests were carried out by exposing fibres of different chemical composition to both lasers and broadband light sources. This allowed us to demonstrate that common, commercially available fibres with pure-silica high-NA core may be used for solar applications. This comes with the advantage of a low cost and a high availability on the market. We also demonstrated that fibres doped with P and Al quickly undergo solarisation processes which lower their transmission efficiency, whereas F- and Ge-doped fibres shows good transparency in the spectral range of interest. As a final step of the study, a prototype daylighting/HCPV module was realised by coupling the best-performing fibres with the primary optics and the solar cells. The engineering of this system were optimised in terms of fibre cabling, power supply and cooling process management, and its efficiency were evaluated by both electrical and luminous measurements.