## 4 Conclusions  
This study reports a new experimental evaluation carried out during daylight for five days in October in Riyadh to investigate the performance of a PV-PCM, a PV/T-PCM, and a low-concentration PV/T-PCM when compared to a PV panel without cooling. The chosen PCM was Rubithem RT-47, which has a melting temperature of 41-48 \({}^{\circ}\)C and is suitable for the ambient temperature of Riyadh. This study revealed that the combined passive-active cooling system, namely the PV/T-PCM, attained the best daily average electrical efficiency with 5% increase compared to the reference PV panel. The additional thermal power recovered from the PV/T-PCM brought up the overall efficiency of the PV/T-PCM to 42.7%. Coupling low solar concentration with the PV/T-PCM system was very effective for about two hours around noon, resulting in an 11% increase in electrical power, while the average electrical power over the day was the lowest. However, using the LCPV/T-PCM attained a maximum daily average overall efficiency of 46.5% on Day 5. October is one of the best months in Riyadh in terms of higher-than-normal irradiance and moderate ambient temperatures which can lead to a good performance for a PV panel without cooling, compared to the summer season. This study reveals that, even within months beyond the severe conditions, there is a need for an efficient cooling approach to boost PV system performance. In addition, the present study shows the workability of using an active-passive cooling approach that uses a PCM with a high melting point even on off-summer days to improve the PV system performance. The solar low concentration coupled with the PV/T-PCM system needs further experimental investigations that may include different configurations and/or simple tracing systems to avoid shading effects and extend the higher-performance period. Figure 9: The average overall efficiency of the four PV panels: (**a**) over the day from 9:30 to 16:30, and (**b**) around noon from 11:00 to 13:00. **Author Contributions:** Conceptualization, M.B.E. ; Methodology, M.B.E. and Z.A. ; Software, S.Z. and A.A.; Validation, S.Z., O.Z., H.A. and A.A.; Formal analysis, M.B.E. ; Investigation, M.B.E. and S.Z. ; Resources, O.Z. and Z.A. ; Data curation, S.Z., H.A. and A.A.; Writing--original draft, M.B.E. and S.Z. ; Writing--review and editing, M.B.E., O.Z. and H.A. ; Visualization, S.Z. and H.A. ; Supervision, M.B.E. and Z.A. ; Project administration, Z.A. ; Funding acquisition, M.B.E. All authors have read and agreed to the published version of the manuscript. **Funding:** The authors extend their appreciation to the Deputyship for Research & Innovation, \"Ministry of Education\" in Saudi Arabia for funding this research work through the project no. (IFKSURG-2-048). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Conflicts of Interest:** The authors declare no conflict of interest. **Nomenclature**  
\(A\)Area (m2)  
\(Cp\)Specific heat (J/kg K)  
\(D\)Diameter of tube (mm)  
DC Direct Current (A)  
HP Horsepower  
I Current (A)  
\(I\)Irradiance (W/m2)  
\(L\)Concentrator length (mm)  
\(m\)Mass flow rate (kg/s)  
\(P\)Power (W)  
\(Re\)Re Reynolds number  
\(T\)Temperature (\({}^{\circ}\)C or K)  
\(V\)Voltage (V)  
_Abbreviations_  
ACPC Asymmetric compound parabolic concentrator  
BIPV  
Building-integrated photovoltaic panel  
LC Low concentrations  
LCOE  
Levelized cost of energy  
LCPV  
Low concentrated photovoltaic  
NREP  
National Renewable Energy Program  
PCM  
Phase-change material  
PV Photovoltaic  
PV/T  
Photovoltaic tube/thermal  
PWM  
Pulse-width modulation  
_Greek Letters_  
\(\theta^{\prime}\)Internal angle  
\(\theta\)External angle  
\(\eta\)Efficiency (%)  
\(\mu\)Fluid viscosity (Pa. s)  
\(\rho\)Fluid density (kg/m3)  
_Subscript_  
a  
Input radius  
acc  
LCPV acceptance angle  
e  
Exit  
Electrical  
\(i\)  
Inlet  
\(max\)Maximum power  
out  
LCPV output angle  
Overall efficiency  
r  
Exit radius