Table 5.

The module's equations [73].

Description	Equations
Thermal section	$Q_u=m\cdot c_p\cdot (T_o-T_i)=h_f\cdot A_s\cdot (T_s-T_f)$ $Q_{\text{L}}=[h_w\cdot (T_g-T_{\alpha })+{\epsilon }_g\cdot \sigma \cdot (T_g^4-T_{\alpha }^4)]\cdot A_{g,o}=\frac{A_p\cdot \sigma \cdot (T_g^4-T_{\alpha }^4)}{\frac{1}{{\epsilon }_p}+\frac{1-{\epsilon }_g}{{\epsilon }_g}\cdot \frac{D_p}{D_{g,i}}}$ $Q_s=A_a\cdot G_T$
Thermal efficiency	$\eta =\frac{Q_u}{Q_s}$
Total heat loss coefficient	$U_L(Absorber-Glass)=\frac{\sigma \cdot (T_p^4-T_g^4)}{\frac{1}{{\epsilon }_p}+\frac{1-{\epsilon }_g}{{\epsilon }_g}\cdot \frac{D_p}{D_{g,i}}}\cdot \frac{1}{T_p-T_a}$ $U_L(Glass-Ambient)=\frac{h_w\cdot (T_g-T_a)+\epsilon \cdot \sigma \cdot (T_p^4-T_g^4)}{T_p-T_a}\cdot \frac{A_{g,o}}{A_p}$
Optical efficiency	${\eta }_{\mathrm{opt},\Theta }={\gamma }_{\Theta }\cdot (\tau \cdot \alpha )\cdot [1-(1-\rho )\cdot \frac{Q_{R,0}}{Q_s}]={\gamma }_{\Theta }\cdot (\tau \cdot \alpha )\cdot f\left(\rho \right)$