The semitransparent PV laminate has three layers: the exterior layer is clear glass, the middle layer is formed by the PV cells and EVA in the spaces among them, and the third layer can be translucent Tedlar or glass, depending on the typology. The rear glass varies from a single glass in the simplest case, to a triple glaze. The governing equation and the boundary conditions within each layer are:

dT

pcp — — V-(kVT ) = Q

T = Te in x = ePV (4)

kVT • n = hco (To — Tc) + hrcs (Ts — TcJ) in x = 0

Where: p is the density of each layer (Kg/m3); cp is the specific heat coefficient (J/Kg°K); Tis the temperature of the layer (°K); к is the thermal conductivity (W/m°K); Q is the volumetric heat source (W/m3), Te is the temperature of the last node (°K); Tc is the temperature of the first node (°K); Ts is the radiative sky temperature (°K); h co is the average convection heat transfer coefficient between the PV and the exterior (W/m2°K); hrsc is the radiation heat transfer coefficient (W/m2°K) and epv is the thickness of the PV laminate (m). Equation 4 is solved using a finite element scheme in one dimension. The temporary term is discretized using the trapezoidal rule. By deriving the weak form of Equation 4 and applying the Galerkin method, we can obtain a discretized system of equations defined as:
[A\rn+e]=rn+e]

Where: [A] is the coefficients array; [T+e>] is temperatures vector at time step=n+0; [f+&] is the residual array; n is the time step number; 0is the temporal coefficient. When 6=1, the backward Euler scheme is used and when в=1/2 the Crank-Nicolson scheme is used. The array [A] is three-diagonal. The values of the terms in each array depend on the layer. The physical properties of the second layer of the PV laminate (PV cells and EVA) are affected by the packing factor (P). In the case of the rear glass, the FEM discretization will be the same as the PV laminate, but the boundary conditions will be the opposite (Dirichlet at x=0 and Newmann at last node). The system of equations in both domains is solved using a direct three-diagonal algorithm (TDMA). Once the temperatures of each node are obtained, the conduction heat flux towards the air channel q” cond and q”g 1 cond are computed using

Fourier’s law.