## 5 Estimation of the Available Energy and Biogas Costs  
Based on standard measurements and information according to IEA [27], the calorific value of biogas H\({}_{\text{Biogas}}=6.5\) kWh/m\({}^{3}\) and the overall electrical efficiency \(\eta_{\text{el}}=30\%\). Considering Idlib's population is one million, and the average of biogas per person is 0.022 m\({}^{3}\), the approximate annual electrical production for Idlib City would be as follows:  
\[\text{E}_{\text{ww}}=0.022\times 1,000,000\times 6.5\times 0.3\times\frac{365}{1000 }=15,658.5\text{ MWh}_{\text{el}}/\text{year} \tag{3}\]  
However, the municipal waste contains organic materials at a rate of 47.4%, and thus, each ton can produce approximately 81 kWh\({}_{\text{el}}\) of electrical energy [28], which means the following for the city of Idlib:  
\[\text{E}_{\text{msw,c}}=81\times 260\times\frac{365}{1000}=7668.9\text{ MWh}_{\text{el}}/\text{year}\]  
The total annual production available for the city of Idlib from sewage and municipal waste is as follows:  
\[\text{E}_{\text{ww,msw,c}}=15658.5+7668.9=23,327.4\text{ MWh}_{\text{el}}/\text{year}\]  
Throughout the Idlib governor, approximately 1000 tons of municipal waste are produced daily [29], which could generate annual electrical energy as follows:  
\[\text{E}_{\text{msw,g}}=81\times 1000\times\frac{365}{1000}=29,565\text{ MWh}_{\text{el}}/\text{year}\]  
However, the cost of transporting this waste (740 tons) from relatively distant areas to the station must be considered, which adds additional expense to the basic cost. The total electrical production for the Idlib area (sewage for the city of Idlib + municipal waste for the Idlib area) is as follows:  
\[\text{E}_{\text{ww,msw,g}}=15,658.5+29,565=45,223.5\text{ MWh}_{\text{el}}/\text{year}\]  
Biogas costs vary depending on the technology used and the plant's location. According to the global energy report on biomethane and biogas published in 2022 [30] (prices recorded for 2018), the following is derived:  
For the digesters relying on sewage treatment plants: USD/MBtu 14.6 distributed as follows: USD/MBtu 4.3 for maintenance and operation; USD/MBtu 10.3 for construction cost. In terms of percentage, approximately 30% is spent on maintenance and operation and 70% on construction costs. For large digesters: USD/MBtu 9.3 (USD/MBtu 4.1 for maintenance and operation; USD/MBtu 5.2 for construction costs), with percentages of 44% for maintenance and operation and 56% for construction costs. With an operating ratio of 19% for the wastewater treatment plant based on sewage waste and 81% based on organic municipal waste the following is derived:  
The expected cost is C\({}_{\text{biogas}}\) = 0.19 \(\times\) 14.6 \(+\) 0.81 \(\times\) 9.3 = 10.307 USD/MBtu;  
It is distributed as follows:  
Construction cost: C\({}_{\text{biogas,inv}}\) = 10.307 \(-\) 4.138 = 6.139 USD/MBtu;  
Maintenance and operation: C\({}_{\text{biogas,oRem}}\) = 0.19 \(\times\) 4.3 + 0.81 \(\times\) 4.1 = 4.138 USD/MBtu. Regarding percentages, approximately 60% are construction costs and 40% are maintenance and operating costs. Greenius 4.9.0.1 relies on the EUR in its computations; thus, all pricing should also be in EUR. The cost in EUR is as follows: C\({}_{\text{biogas}}\) = 10.89 \(\times\) 0.828 = 9 EUR/MBtu;  
The overall energy yield is \(\eta_{\text{total}}\) = \(\eta_{\text{cycle}}\)\(\times\)\(\eta_{\text{boiler}}\) = 0.35 \(\times\) 0.9 = 0.315 (according to the Greenius modeling program), where:The cycle efficiency (\(\eta_{\rm cycle}\) = 0.35) is the thermodynamic cycle efficiency, and the boiler efficiency \(\eta_{\rm boiler}\) = 0.9. Consequently, taking into consideration that 1 MBtu = 293 kWh, the net cost of electricity is as follows:  
\[C_{\rm el,biogas,total}=9/0.315=28.57\ \rm EUR/MBtu=0.0975\ \rm EUR/kWh.\]  
The cost is divided into the following:  
Investment cost: \(C_{\rm el,biogas,inv}\) = 0.60 \(\times\) 0.0975 = 0.0585 EUR/kWh;  
Maintenance and operation: \(C_{\rm el,biogas,okem}\) = 0.40 \(\times\) 0.0975 = 0.039 EUR/kWh.