# Renewable Energy-Based Energy-Efficient Off-Grid Base Stations for Heterogeneous Network
## 4 Results' Analysis
### Energy Sharing  
According to the flow diagram in Figure 5, excess energy has been shared through a low resistive physical line among the adjacent BSs. The value of the resistance of the interconnected line has been taken from the American Wire Gauge (AWG) standard conductor size table, which is 3.276 \(\Omega\)/km [59]. The inter-cell distance is calculated as \(\sqrt{3}\) times of the cell radius (i.e., \(\sqrt{3}\)R) and the cell radius is 1000m for \(P_{TX}=20\) W. The total resistance of the transmission line between the two BSs is 5.67 \(\Omega\). We use the cell radius of macro, micro, pico and femto BSs as 1000m, 500m, 200m and 10m, respectively. This energy sharing among the BSs for the heterogeneous network ensures the optimum use of RES and avoids any type of blackout or power shortage. The percentage of energy savings with the total amount of shared energy for different system bandwidth and sharing policies is demonstrated in Tables 9 and 10, respectively. The results demonstrate that around 10% to 21% of the total energy can be saved every year by applying the proposed macro-macro energy-sharing technique. The proposed system ensures energy efficiency (\(\eta_{EE}\)) under dynamic traffic profile and can save a considerable amount of energy loss by the energy sharing technique. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sharing** & \(E_{excess}\) **(kWh)** & **Resistance (\(\Omega\))** & \(E_{loss}\) **(kWh)** & \(E_{share}\) **(kWh)** \\ \hline Macro-Macro & 2056 & 5.67 & 1187.20 & 868.79 \\ Micro-Macro & 128 & 1.70 & 1.34 & 126.66 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Amount of shared energy and percentage of energy-saving for inter BS sharing mechanism under 10 MHz. Figure 17: Bio-feedstock consumption. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**BW (MHz)** & \(E_{gen}\) **(kWh)** & \(E_{D}\) **(kWh)** & \(E_{excess}\) **(kWh)** & **I (Amp)** & \(E_{loss}\) **(kWh)** & \(E_{share}\) **(kWh)** & \(E_{save}\) **(\%)** \\ \hline
5 & 5548 & 3896 & 1295 & 3.07 & 470.87 & 824.12 & 21.15 \\
10 & 7674 & 5120 & 2056 & 4.88 & 1187.20 & 868.79 & 16.9  
A critical analysis of the associated costs to the proposed system has been represented in this section. These analyses have been conducted via the HOMER optimisation software to propose a reliable and optimum cost-efficient green supply system. Nominal cash flow summary for the proposed system of macro, micro, and pico BSs have been respectively shown under the 10 MHz system BW in Figures 18-20. The cash flow summary of femto BS is identical to pico BS. For all the demonstrated configurations, the capital cost (CC) has the highest value, and the replacement cost (RC) has the second-highest value. For macro BS, CC for the PV array is $3,500 (panel size 3.5 kW, cost $500/0.5 kW), operation and maintenance cost (OMC) is $378 (panel size 3.5 kW, cost around $10/1 kW), RC is zero because the PV array has a lifespan of 25 years, which is more prolonged than the project lifespan. The salvage value for that extra five years is $190. For other BSs, different costs of PV array have been calculated in the same fashion. For both macro and micro BS configurations, a single BG is required, which costs $660. OMC and fuel cost (FC) vary in generation. The salvage value is inversely proportional to the BG use. The number of batteries is always a multiple of 8 because the DC bus bar voltage is 48V (Each battery's nominal voltage is 6V). CC for each battery is $300. RC depends on battery lifetime. Battery lifetime can be calculated from Equation (26). RC of each battery is also $300. Less use of battery extends the battery lifetime. Higher battery lifetime minimizes the overall RC of the battery for the system. The OMC of the battery is $10/unit/year. Thus, 32 batteries cost $320 per year. However, due to the discount factor, this costs less in the long run. The CC, RC, and OMC of the converter depend upon the quantity of use. CC and RC are both $.4/Watt and OMC is $.01/Watt/year. More BG generation costs more for the converter.