# Renewable Energy-Based Energy-Efficient Off-Grid Base Stations for Heterogeneous Network
## 4 Results' Analysis
### Energy Generation and Consumption  
The yearly energy consumption (DC and AC load) including excess energy for the macro, micro, pico, and femto-cell networks under 10 MHz bandwidth are summarised in Table 8. This excess energy is used as a backup, either for charging the battery or for sharing in need of other BSs. DC load is the main energy consumer. It is assumed that a bulb as an AC load is the only connected macro BS.  
The individual energy generation breakdown of the proposed off-grid hybrid system is illustrated in Figure 11. For the simulation, the dynamic profile of the RES (Figures 3 and 7) has been considered. Here, the results are only shown for the 10 MHz system BW. For all cases, the solar PV is the main energy contributor. In the proposed model, macro BSs can share energy to another macro, micro, pico, and femto BSs. Consequently, more excess electricity has been generated in the case of the macro BSs. The rest of the BSs use the excess electricity as a backup in case of a shortage or outage of RES. In the case of shortage, these BSs can share excess electricity only to the mother macro BS.  
The periodic monthly statistics of the power generation by the different RES for different BSs are separately illustrated in Figures 12 and 13. Solar PV is the main contributor  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline
**BW** & \multicolumn{3}{c}{**PV (kW)**} & \multicolumn{3}{c}{**BC (kW)**} & \multicolumn{3}{c}{**Battery(units)**} & \multicolumn{3}{c}{**Converter (kW)**} \\ \hline
**(MHz)** & **Macro** & **Micro** & **Pico** & **Femto** & **Macro** & **Micro** & **Pico** & **Femto** & **Macro** & **Micro** & **Pico** & **Femto** & **Macro** & **Micro** & **Pico** & **Femto** \\ \hline
5 & 2.5 & 0.5 & 0.1 & 0.1 & 1 & 1 & - & - & 32 & 24 & 8 & 8 & 0.1 & 0.1 & - & - \\
10 & 3.5 & 0.5 & 0.1 & 0.1 & 1 & 1 & - & - & 32 & 24 & 8 & 8 & 0.1 & 0.1 & - & - \\
15 & 4 & 1 & 0.1 & 0.1 & 1 & 1 & - & - & 32 & 24 & 8 & 8 & 0.1 & 0.1 & - & - \\
20 & 4 & 1 & 0.1 & 0.1 & 1 & 1 & - & - & 32 & 24 & 8 & 8 & 0.1 & 0.1 & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 7: An optimal size of the hybrid solar PV/BG system.  
Figure 11: Individual energy breakdown for 10 MHz system bandwidth.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Items** & **Macro** & **Micro** & **Pico** & **Femto** \\ \hline AC load (kWh/yr) & 130 (3\%) & 0 (0\%) & 0 (0\%) & 0 (0\%) \\ DC load (kWh/yr) & 4989 (97\%) & 1117 (100\%) & 123 (100\%) & 87.2 (100\%) \\ \hline Excess energy (kWh/yr) & 2056 (26.8\%) & 128 (9.41\%) & 81.3 (37.6\%) & 121 (55.9\%) \\ \hline \hline \end{tabular}
\end{table}
Table 8: Energy consumption breakdown for 10 MHz system bandwidth.  
throughout the year and BG contributes to that period when solar intensity is relatively low. It is clear that the proposed system can minimize the capital costs and carbon contents because the solar PV generates a large of consumed energy for the overall heterogeneous setup. On the other hand, the system is also reliable because of the presence of BG and the energy sharing technique.  
A broad evaluation of the annual energy contributed by the different sources under various system BWs has been illustrated in Figures 14 and 15, where it is clear that with an increase in system bandwidth, the generation is increased. If the solar PV cannot bear the load because of cost efficiency, BG will take its place. In the case of pico and femto-cells, with the increment of the system BW, the excess electricity will decrease to cope up with the load. It is better for the system performance, as the setup will not change under different system BWs.  
Figure 14: Energy breakdown under different system BW for the macro (**left**) and micro (**right**) BS.  
Figure 12: Monthly power contribution by the RES under 10 MHz for macro (**left**) and micro (**right**) BS.  
Figure 13: Monthly power contribution by the RESs under 10 MHz for pico (**left**) and femto (**right**) BS.