Operational and architectural aspects for building integrated Concentrating PV/Ts

Considering the building integrated Concentrating PV and PV/T systems, there are some operational and architectural aspects. A first notice is that in PV/T systems the cost of the thermal unit is the same either the PV module is crystalline-silicon (c-Si), poly-crystalline silicon (pc-Si) or amorphous-silicon (a-Si). Thus the ratio of the additional cost of the mounted thermal unit per PV

module area cost is different and is almost double in case of using a-Si compared to c-Si or pc-Si PV modules. The complete PV/T systems include the necessary additional components (Balance Of System, BOS, for the electricity and the BOS system for the heat) and therefore the final energy output is reduced by about 15% due to the electrical and thermal losses from one part to the other. Water hybrid PV/T systems can be used during the whole year for the pre-heating of water, since the temperature of water in the water supply network is no more than 20° C, even during summer months. Considering the installation of solar energy systems on building roof or facade, the combination of PV/T collectors with solar thermal systems have some aesthetic problems due to the different size and appearance. The problem can be overcome if there is a harmony in size and if solar thermal collectors have absorbers with same or similar color to the color of PV cells.

image193

Based on the investigated CPV and CPVT systems some new architectural designs have been performed, giving a better idea about the aesthetic integration of them on building structure. In Fig. 7 the design of an industrial building with booster reflectors on the roof shows an example of an effective integration of them on building roof. Another design with collectors on building roof is that of Fig. 8, where CPC type solar collectors with PV/T absorber are used. The Fresnel lenses with linear absorbers are shown in the three designs of Fig. 9. The first design is the case of the sunspace (Fig. 9, left) and the other two designs demonstrate the case of atrium with the absorbers out of focus (Fig. 9, center) and on focus (Fig. 9, right), showing the effect of shading.

image194
The design of Fig. 10 is referred to the integration of CPC reflectors on building structure. The building balconies can be used to put the reflectors, which can have the parabolic form and the reflected radiation to be focused on the back of the front building. In case of using stationary reflectors the focal line is moving up and down, depending on sun height, while in case of moving reflectors the focal line can be stable. In both cases, the sun faced building surface is lighted by the not reflected radiation and the reflected diffuse radiation illuminates the back of the front building.

3. Conclusions

Low concentration solar energy configurations have been investigated and studied regarding the effect of the concentrator type to the performance of CPV and CPVT systems. We have studied flat diffuse reflectors, which provide an almost uniform distribution of solar radiation on PV surface, linear Fresnel lenses, which achieve additionally solar control of interior spaces and CPC reflectors, which can effectively combine PV strips with flat solar thermal absorbers. The absorbing solar radiation increases cell temperature and reduces electrical efficiency, but several modes for efficient and cost effective heat extraction can be applied and the most appropriate, according to the application requirements, can be selected. These new concentrating collectors can be integrated on buildings being adapted with their architecture and contributing to the energy and the aesthetic requirements of it.

Acknowledgements

The contribution of the architect Maria Tripanagnostopoulou to the designs of the paper is warmly acknowledged

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