# A Brief Overview of Energy Efficiency Resources in Emerging Wireless Communication Systems
## 3 Energy Efficiency Techniques in Wireless Communication Systems
### Renewable Energy Resources  
Renewable energy is a type of energy from natural resources like the sun, wind, etc. [36]. Part of the relevance of renewable energy is the supply of energy to areas with low or difficult accessibility to power grid sources [37]. By using renewable energy resource in wireless communication, a lower operational cost accrues to produce the same amount of energy that would have been provided if other means, like a diesel generator, were applied. Thus, equivalent information can be transmitted at a much higher operational cost when renewable energy is not used, resulting in energy inefficiency. Other relevance of renewable energy resources is environmental friendliness; renewable energy resources do not produce too many gas emissions compared to diesel generators [38]. Since less emissions are produced, most natural energy is transformed into useful electrical energy.  
Different natural resources can be used as renewable energy technology. Some include hydropower, biomass, wind, hydrogen, geothermal, solar (photovoltaic and solar thermal), and ocean power [39]. Deploying large scale renewable technologies is challenging and has a high initial installation cost. Nevertheless, it has an optimum operational cost that outweighs the operational or running cost for the normal and frequently used energy supply (diesel generators) [40]. Factors affecting this are increased and unstable oil prices, air pollution, cost of transportation, epileptic energy supply, etc. [41]. British Columbia's transmission network deployed Bear Mountain Wind farm (BMW) as their first large-scale wind farm. Several communication devices were integrated with the wind farm, mainly wired technology. Communication availability can be enhanced, and also the maintenance effort can be reduced if the communication equipment is scalable and interoperable. The Bear Mountain Wind farm had thirty-four turbine generators which produced 102 MW [42]. Another interesting renewable energy source adopted is photovoltaic power systems [43; 44].  
A PV cell, usually encapsulated as a module, is used to harvest energy from the sun, converting it to electrical energy. To make an array meet the desired current or power, strings, a collection of PV modules, are interconnected. Strings have a series connection, thus, the greater the number of strings, the higher the voltage [45; 46]. A typical representation of the cell, module, panel and array architecture of PV is shown in Figure 1[47]. Utility, commercial and residential scales are the three classifications of grid-connected solar systems. Installations above 100 kW are designated as utility scales or solar farms/plants,and installations commonly found on the roof of a building with commercial capacity range from 10 kW to 100 kW [46]. The smallest type of installation found on private properties is the residential scale of less than 10 kW [46, 48]. Cell ageing, soiling, partial shading, dust collection, and cell damage are examples of unavoidable non-optimal conditions that affect the power output of a photovoltaic array. Integrating a sensor that sends information data to the monitoring interface after sensing the temperature, voltage, and current is a way to track the solar module status. The major shortcomings of a photovoltaic cell system are troubleshooting failed panels and minimizing power dissipation losses [42].