## 8 Conclusions  
This study convincingly demonstrated the benefits of combining solar CSP and AD biogas production based on municipal solid waste (MSW) and wastewater treatment in the Idlib governor. The application of this study can help secure a renewable energy source in addition to the following benefits: ensuring the stability of the electricity produced, disposing of the wastes in a clean, energy-producing way, producing biofertilizer, and creating new job opportunities for the local community. Modeling operations were conducted for each case of the studied cases practically, as well as for the case corresponding to the highest growth rate of methanogenic bacteria theoretically; the modeling processes were conducted at 11 different values of storage capacity from FLHs = 0 to 10 and by varying the SM from 1 to 8. This study showed that when operating as a net solar plant, the lowest value for the LCOE was 0.1785 EUR/kWh at FLHs = 5 and SM = 2, while the annual electricity production was 25.21 GWh. The maximum annual electricity production is 48.66 GWh, achieved at FLHs = 10 h and SM = 8, and the LCOE = 0.2896 EUR/kWh. It is possible to obtain an annual electrical energy production of 39.7 GWh, which is about 82% of the maximum possible annual production, at a cost of LCOE = 0.1864 EUR/kWh. The LCOE is 5% higher than the lowest possible cost in this case. When operating the system as a hybrid plant with an annual capacity factor of 1, it was discovered that the lowest value of energy produced was in the third scenario at \(\text{t}_{\text{AD}}=\) 43.52 \({}^{\circ}\)C and \(t_{c}=\) 63.5 \({}^{\circ}\)C), with FLHs = 0 h and SM = 1; the LCOE = 0.1283 EUR/kWh. \begin{table}
\begin{tabular}{c c c c} \hline
**Operation Case** & **Biogas Net** & **Solar Net (CSP)** & **Hybrid (CSP + Biogas)** \\ \hline Rated Net Capacity (kWel) & 9987 & 9987 & 9987 \\ \hline Annual Energy production (GWhel) & 45.22 & 25.21/39.70 & 87.48 \\ \hline Annual Power Factor & 0.5 & 0.29/0.45 & 1 \\ \hline Annual Electrical Efficiency (\%) & 30 & 11/10 & 20 \\ \hline Solar Share (\%) & 0 & 100 & 14 \\ \hline LCOE (EUR/MWh) & 157.0 & 178.1/186.4 & 128.3 \\ \hline \end{tabular}
\end{table} 
Table 8: Key findings of the hybrid power plant in consideration of operation cases (biogas-solar-hybrid). \begin{table}
\begin{tabular}{c c c c c} \hline
**Location** & **Reference** & **Hybrid Proposal** & **DNI (kWh/Year)** & \
\begin{tabular}{c} **Nominal** \\ **Capacity (MW)** \\ \end{tabular} & **LCOE (EUR/kWh)** \\ \hline Tunis & [PERSON] et al. [34] & CSP–Biomass & 1922 & 1 electricity/CHP & 0.175/0.126 \\ \hline Messaad, Algeria & [PERSON] et al. [35] & CSP–Biomass & 2630 & 5 & 0.097 \\ \hline Madrid, Spain & [PERSON] et al. [13] & CSP–Biomass & 2000 & 10 & 0.153 \\ \hline Natal, Brazil & [PERSON] et al. [36] &
\begin{tabular}{c} CSP–Biomass + \\ desalination \\ \end{tabular} & 2200 & 100 & 0.065 \\ \hline Lleida, Spain & [PERSON] et al. [37] & CSP–Biomass & 1812 & 22.5 & 0.270 \\ \hline \end{tabular}
\end{table} 
Table 9: LCOE for CSP–biomass hybrid power plant for various locations. In the end, it can be concluded that the hybrid solar-biogas system significantly reduced electricity costs compared to pure solar energy or pure biogas energy only and achieved a competitive price compared to the prices of the electricity grid in Idlib. Methodology, A.F.A. ; Software, A.A.K.A. ; Validation, R.A.A. ; Formal analysis, A.F.A. ; Investigation, R.A.A. ; Resources, A.A.K.A. ; Data curation, A.A.K.A. ; Writing--original draft, A.A.K.A. and A.F.A. ; Writing--review & editing, R.A.A. ; Supervision, R.A.A. ; Funding acquisition, R.A.A. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request. The researchers would like to thank the Deanship of Graduate Studies and Scientific Research at Qassim University for financial support (QU-APC-2024).