Fluorescent solar collectors

Some 60 dyes have been selected as possible photovoltaic materials their electrochemical redox potentials, surface adsorption, spectroscopic properties, fluorescence yields, and acid-base properties have been measured. The aim of this work is to produce a low-cost panel for harvesting solar energy as electrical power. The physical principles of fluorescent solar collectors have been discussed by Raue and Harnisch and several classes of dyes examined. Coumarin dyes are suitable convertors, particularly if the amino-group is fixed by ring closure to the aromatic system. 

Luminescence Fluorescence solar collector Rhodamlne-doped silica film (Reisfeld, 1990)... 

Figure 10.8 Design of a fluorescent dye-based solar collector...

Other Aluminosilicates, Transparent mullite glass-ceramics can be produced from modified binary Al C —Si02 glasses (21). In these materials, the bulk glass phase separates into tiny alumina-rich droplets in a siliceous matrix. Further heat treatment causes these droplets to crystallize to mullite spherulites less than 0.1 Jim in size. When doped with ions such as Cr3+, transparent mullite glass-ceramics can be made to absorb broadly in the visible while fluorescing in the near-ii (22,23), thereby making them potentially useful for luminescent solar collectors. 

Goetzberger, A. and Wittwer, V. (1979) Fluorescent planar collector-concentrators for solar energy conversion. Adv. Solid State Phys.,... 

Reisfeld, R. and Kalisky, Y. (1981) Nd and Yb germanate and tellurite glasses for fluorescent solar energy collectors. Chem. Phys. Lett, 80, 178-183. 

Bahners et al. [68] investigated the concepts of technical fibers for the special coated fibers to be used for textile solar collectors. The technical fiber made of different polymers (polymethyl methacrylate (PMMA) and polyethylene terepthalate (PET)) were characterized with respect to optical properties relevant for the model. The fibers were coated with a matrix of 5% polyvinyl acetate (PVA) in methanol, into which fluorescent dyes were dispersed. The wave guiding behaviors of the technical fiber over greater lengths were quantitatively analyzed by a logarithmic fit. The measured value was found to divert from the ideal fit at larger fiber lengths. 

The main reasons for the low efficiencies are the incomplete absorption of the solar spectrum by any single material which serves as a colorant. Self-absorption of the fluorescence by the emitting colorant. Critical cone losses of the reemitted centers, absorption and scattering of the host materials, lack of good contact between the LSC and the photovoltaic cell. Reflection of light from the metallic surfaces of which the electrical contacts are made. The decrease of performance efficiency of the collectors made of organic dyes with time are a result of photodecomposition of the colorant and polymeric host material. 

Efficient LSCs are based on the entrance of solar radiation into a homogeneous medium of collector containing a fluorescent species in which the emission bands have little or preferably no overlap with the absorption bands. 

A system undergoing excited-state intramolecular proton transfer was suggested as a solar energy collector. Moreover, since such systems reveal a very large Stokes shift due to the excited-state intramolecular proton transfer (ESIPT) reactions, resulting in the phototautomeric fluorescence with a relatively high quantum yield (about 30%), they are recommended as potential solar energy concentrators. 

Goetzbeiger, A. and Greubel, W. (1977) Solar energy conversion with fluorescent collectors. Appl. Phys., 14 (2), 123 139. 

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