4.7. Electricity generated by the PV

The electricity generated by the PV cells must be expressed as:

q’’e ={Tcc)nIAMPvGtpvpv (W/m2) (10)

where: t]pV is the PV efficiency. The PV efficiency is depending on the PV cells temperature and on the incident radiation. To consider these two factors, a linear variation model has been adopted.

2. Prototypes and monitoring strategy

A distinction should be made between the determination of the energy efficiency at component/fa? ade level and at building level. For this reason, the experimental activity will be divided in two stages and two different prototypes will be constructed. The first stage consists in the construction of a small system, very similar to TRE [8], formed by a single PV module tested under forced convection situations. The 8 new modules of ISOFOTON will be tested to obtain specific data about heat exchange and electricity performance. The second stage will be the construction of a more sophisticated system to test the best configuration of PV module under real conditions. This phase will start using the test cells of the Politecnico of Torino and later, the construction of similar cells in Lleida will be carried out. During August and September 2008 the monitoring task will start and it will be extended until the end of 2009. In the figure 3 the schemes for the first prototype are shown.

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Подпись: Fig.3. PV Schemes of the first prototype at the ITL in Lleida. Cross section and front view.

Conclusions

A strong thermodynamic coupling exists between the air flow through the naturally ventilated double­skin fa? ade and the air temperature difference between the cavity and the outside. This interaction can only be predicted by sophisticated building energy modelling and simulation techniques as was done in the current study. Three new TRNSYS types have been developed and validated through numerical experiments. One first prototype has been constructed at the University of Lleida and the monitoring
period has just started. Experimental results to validate the TRNSYS types and to get some conclusions about the 8 new PV modules are expected to be available by the middle of 2009.

Concerning to the convective heat transfer and the mass flow rate within the air gap, this research has showed that there is still a lot of work to be done to clearly define the performance under transient turbulent free convection.

The first standardized typologies defined within this research will be further refined and included in the second prototype. Once they are validated under real conditions, the manufacturing process as well as the commercial strategy will be defined.

References

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[9] Kakag S., R. Shah and W. Aung. 1987. ‘Handbook of single-phase convective heat transfer’. Wiley.

[10] Kays W., Crawford M. and Weigand B. 2004. ‘Convective Heat and Mass Transfer. McGraw Hill.

[11] Mei L., Infield D., Eicker U., and Volker F. 2003. ‘Thermal modelling of a building with an integrated ventilated PV facade’. Energy and Buildings. 35.

[12] Parretta A., Sarno A., and Yakubu H. 1999. ‘Non-destructive optical characterization of PV modules by an integrating sphere.: Part I: Mono-Si modules’. Optics Communications.161.

[13] Ramanathan S. and Kumar R. 1991. ‘Correlations for natural convection between heated vertical plates’. Journal of Heat Transfer. 113.

[14] Rohsenow W., Hartnett J. and Cho Y. 1998. ‘Hanbook of Heat Transfer. McGraw Hill.

[15] Saelens D. 2002. ‘Energy Performance Assessment of single storey multiple-skin facades’. Katholieke Universiteit Leuven — Faculteit Toegepaste Wetenschappen.

[16] Sharples S. and Charlesworth P. 1998. ‘Full-scale measurements of wind-induced convective heat transfer from a roof-mounted flat plate solar collector’. Solar Energy. 62 -2.

[17] Siegel R. 2002. ‘Thermal Radiation Heat Transfer’.Taylor and Francis.

[18] Wouters P. and Vandaele L. 1994. ‘The PASSYS services: summary report’. European Commission Publication No. EUR 15113 EN

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