## 3 System Architecture
### SPV/WTG Power Subsystem  
The solar power supply system consists of various elements (as listed below) that all contribute to energy savings, and have to be designed in a way that allows easy disassembling and component separation for recycling.  
1. Solar panels: responsible for absorbing shortwave irradiance and converting light into direct current (DC) electricity [23].
2. WTG: responsible for converting wind energy to a regulated power which can be connected to the DC-power bus. Generally, for a small power load, vertical style windmills show some special benefit [23].
3. Regulator charger: the highest power demand in a typical BS is based on 48 V\({}_{\text{dc}}\) voltage. Therefore, it is beneficial to use DC/DC solar regulator converters that can directly convert the unregulated DC output voltage and current from a solar panel to a regulated output voltage for the BS equipment to protect the battery bank.
4. Battery bank: stores excess electricity for future consumption by the BS at night, during load-shedding hours or if the available solar energy is not sufficient to feed the BS load completely. To protect the battery, inclusion of a charge controller is recommended. A charge controller or battery regulator limits the rate at which the electric current is added to or drawn from  
\begin{table}
\begin{tabular}{c c c} \hline
**Item** & **Notation** & **Unit** & **LTE Macro-BS** \\ \hline Number of sectors (\(N_{Scat}\)) & \# & 3 \\ Number of antennas (\(N_{Ant}\)) & \# & 2 \\ Number of carriers (\(N_{Carr}\)) & \# & 1 \\ Number of transceivers (\(N_{TRX}=N_{Scat}\times N_{Ant}\times N_{Carr}\)) & \# & 6 \\ \hline Total number of \(N_{TRX}\) chains, \(P_{op}=N_{TRX}\times\) Total per TRX & W & 909.93 \\ \hline Microwave link (\(P_{m}\)) & W & 80 \\ \hline Lamps \(P_{lm}^{AC}\) & W & 40 \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._  
Figure 3: Hourly load profile for the LTE macro-BS.  
electric batteries, preventing overcharging and potentially protecting against overvoltage that can reduce battery performance or lifespan and may pose a safety risk. A charge controller may also prevent complete battery draining (\"deep discharging\") or perform controlled discharges, depending on the battery technology, to protect battery life [23].
* Inverter: An inverter is a device that changes a low DC-voltage into usable 220 V AC voltage. It is one of the system's main elements. Inverters differ by the output wave format, output power and installation type. It is also called a power conditioner because it changes the form of the electric power. There are two types of output wave format: modified sine-wave (MSW) and pure sine-wave. The MSW inverters are economical and efficient; the sine wave inverters are usually more sophisticated with high-end performance that can operate virtually any type of load [23].
* Control system: serves as the brains of a complex control, regulation, and communication system. The most common communication units in the remote interface are wireless modems or network solutions. In addition to the control functions, the data logger and alarm memory capabilities are of high importance. All power sources working in parallel are managed by a sophisticated control system and share the load with their capabilities to accommodate the fact that power shortages are not admissible in the cellular telephony sector.