The convection heat transfer between the glass layer of the PV laminate and the exterior follows the Newton’s law of cooling. In 1984, Sharples [16] concluded that the linear correlations obtained for solar collectors, are also valid for ventilated facades. The convective heat transfer between the last layer of the rear glass and the room also follows the Newton law of cooling but the convective heat transfer coefficient is affected by the HAVC system of the building.

4.5 Thermal and Solar radiation. Spectral and angular dependency

The semitransparent PV laminate is divided in two equivalent surfaces: the opaque surface, formed by the sum of the PV cells surfaces and the semitransparent surface, which is the sum of the transparent spaces of the PV module.

The opaque surface has an external glass layer, the EVA layer and the PV cells. The product tau-alpha (та) is the optical property to be determined. The angular dependence was deeply analysed by Parretta

[12] who concluded that an equivalent refractive index, higher than the glass refractive index, must be used. Since reflection at the interface EVA/PV cell is diffuse, the PV absorptance will be independent from the incidence angle and the angular dependence will only affect the transmittance of the glass and EVA joint. The incidence angle modifier (IAMPV) will be used. This IAM will be obtained, for the beam radiation, using Fresnel equations of the air/glass interface.

In the semitransparent equivalent surface an overall hemispherical value has been obtained from the spectral dependency of each layer (glass, EVA and Tedlar). The optical properties of the rear glass are obtained from the TRNSYS database. The angular dependence must include the reflections between the semitransparent surfaces, thus, the net radiation method [17] will be used.

The thermal radiation between the semitransparent surface and the rear glass; between the last layer of the rear glass and the adjacent room and the radiation between the glass of the PV laminate and the sky is determined by solving the net heat transfer between two infinite grey surfaces.