## 5 Conclusions
\begin{tabular}{l l} \(A_{AC}\) & Area of the flat tube (m\({}^{2}\)) \\ \(A_{PV}\) & Total area of the \(PV\) cells (m\({}^{2}\)) \\ \(C_{p}\) & Heat capacity of the water (J/kg\({}^{\circ}\) C) \\ \(CL_{g}\) & Cleanliness factor of the glass (_dimensionless_) \\ \(CL_{m}\) & Cleanliness factor of the mirror (_dimensionless_) \\ \(D_{h}\) & Hydraulic diameter of the flat tube (m) \\ \(d_{i}\) & Separation between \(i-th\) and \(i+1-th\) mirrors (m) \\ \(EG\) & Total useful energy gain (_dimensionless_) \\ \(E_{C}\) & Total useful energy in a configuration (kWh) \\ \(E_{CPV}\) & Total useful energy in \(CPV\) system (kWh) \\ \(E_{NCPV}\) & Total useful energy in \(NCPV\) system (kWh) \\ \(e_{R}\) & Overall uncertainty associated with the measurement (\%) \\ \(f\) & Height of the receiver (m) \\ \(HG\) & Solar irradiation gain (_dimensionless_) \\ \(H_{B}\) & Beam solar irradiation incident (kWh) \\ \(H_{CPV}\) & Solar irradiation incident on the \(PV\) cells (kWh) \\ \(H_{NCPV}\) & Solar irradiation incident on the \(PV\) cells (kWh) \\ \(I_{t}\) & Total absorbed solar irradiance for \(PV\) system (W/m\({}^{2}\)) \\ \(k\) & Thermal conductivity (W/m\({}^{\circ}\) C) \\ \(L_{i}\) & Position of \(i-th\) mirror (m) \\ \(L_{AC}\) & Length of the active cooling system (m) \\ \(L_{M}\) & Length of the mirrors (m) \\ \(L_{PV}\) & Length of the \(PV\) system (m) \\ m & Fluid mass flow rate (kg/s) \\ \(N\) & Number of mirrors on each side of the SSLFR \\ \(P_{rw}\) & Prandtl number of the working fluid (_dimensionless_) \\ \(Q_{cond}\) & Conduction heat transfer (W) \\ \(Q_{conv}\) & Convection heat transfer (W) \\ \(Q_{rad}\) & Radiation heat transfer (W) \\ \(Q_{th}\) & Internal heat generation in \(PV\) cells (W) \\ \(Q_{u}\) & Useful heat (W) \\ \(R_{ev}\) & Reynolds number of the working fluid (_dimensionless_) \\ \(T_{amb}\) & Ambient temperature (\({}^{\circ}\)C) \\ \(T_{AC}\) & Temperature of the flat tube (\({}^{\circ}\)C) \\ \(T_{PV}\) & Temperature of the \(PV\) cells (\({}^{\circ}\)C) \\ \(T_{in}\) & Temperature of the inlet fluid to the secondary system (\({}^{\circ}\)C) \\ \(T_{out}\) & Temperature of the outlet fluid to the secondary system (\({}^{\circ}\)C) \\ \(T_{ref}\) & Reference temperature (\({}^{\circ}\)C) \\ \(T_{w}\) & Working fluid temperature (\({}^{\circ}\)C) \\ \(UHG\) & Useful heat gain (_dimensionless_) \\ \(W_{AC}\) & Width of the active cooling system (m) \\ \(W_{Mi}\) & Width of the \(i-th\) mirror (m) \\ \(W_{PV}\) & Width of the \(PV\) cells (m) \\ \(\alpha\) & Absorptivity of the \(PV\) cell (_dimensionless_) \\ \(\beta_{i}\) & Angle which mirror \(i\) forms with the horizontal (\({}^{\circ}\)C) \\ \(\beta_{M}\) & Angle between the mirror axis and the horizontal plane (\({}^{\circ}\)C) \\ \(\beta_{ref}\) & Temperature coefficient (1/\({}^{\circ}\)C) \\ \(\beta_{S}\) & Angle between the \(PV\) system and the horizontal plane (\({}^{\circ}\)C) \\ \(\delta_{AC}\) & Wall thickness of the flat tube (m) \\ \(\eta_{e}\) & Electrical efficiency of the \(PV\) system (_dimensionless_) \\ \(\eta_{ref}\) & Reference electrical efficiency (_dimensionless_) \\ \(\eta_{th}\) & Thermal efficiency (_dimensionless_) \\ \(\theta_{i}\) & Angle between the vertical and the line centre point of \\  & each mirror with the focal point (\({}^{\circ}\)) \\ \(\theta_{l}\) & Longitudinal incidence angle (\({}^{\circ}\)C) \\ \(\theta_{t}\) & Transversal incidence angle (\({}^{\circ}\)C) \\ \(\theta_{t_{0}}\) & Operation interval (\({}^{\circ}\)C) \\ \end{tabular}