Page 312 - A Comprehensive Guide to Solar Energy Systems

316 A ComPreHenSIVe GuIde To SolAr enerGy SySTemS

From the comparisons shown in Table 14.3, the BIPVT panel presented in this chapter,
is able to harvest solar irradiance more efficiently in form of electricity and heat than most
PVT or BIPVT technologies currently available in the literature. Because of the ability to
control temperatures through the water flow, the PV modules can work at lower tempera-
tures in the summer time, leading to a higher efficiency for PV utilization. Furthermore,
due to the temperature control on the roof, better thermal comfort in the building can be
achieved and, therefore, the energy demand for cooling can be reduced in the summer
time. moreover, the warm water flow can be applied to remove frost or ice on the roof
in wintertime, thus further enhancing solar energy utilization. In addition, as shown in
Tables 14.1 and 14.2, the temperature increase of the collected water, the useful collected
heat, and the increased PV efficiency vary from the water flowing rate and the irradiance
levels. This provides customers with much flexibility to adjust the water flowing rate to
meet their specific requirements.

14.5 Summary and Conclusions

In this chapter state-of-the-art BIPVT systems are discussed; namely a commercial BIT-
erS system developed by Atlantis energy Systems, Inc., and a novel BIPVT solar roof pan-
el developed by Columbia university. As an essential component of the multifunctional
building envelope, a novel FGm panel was successfully integrated into the BIPVT panel.
The FGm layer gradually transits material phases from well-conductive side (aluminum
dominated) to another highly insulated side (HdPe dominated). due to the high thermal
conductivity of the upper part of the FGm, the heat in the PV cells can be immediately
transferred into the FGm and then captured by the cool water flowing in all directions
through the embedded tubes. Thus the elevated operation temperature in the PV cells can
be easily cooled down and as a consequence the PV efficiency can be considerably en-
hanced.
The developed BIPVT panel can be integrated into a building skin with relevant sys-
tem components such as water circulation, flow control, and heat storage. It enables
heat harvesting while improving the efficiency of the PV modules by controlling the
temperature. The electricity can be directly transmitted to the grid, while the heat can
be stored or directly used. This system can be used for the generation of electricity and
heat for both residential and commercial buildings, which in turn reduces the heating
and cooling costs. The performances of the prototype BIPVT panel in terms of its ther-
mal efficiency and PV efficiency have also been evaluated in the laboratory. Test results
showed that
• The increased temperature of the collected water by the BIPVT can be as high as
−2
−1
37.5°C at an irradiance of 1000 W m with a relatively low flow rate at 30 mL min ,
and that the decreased surface temperature of the BIPVT can be as high as 32°C when
−1
the flow rate is increased to 150 mL min . It is expected that, as the water flow rate
increases, the BIPVT surface temperature will further decrease.