C. Advantages and Disadvantages
The one factor that is common to all renewable technologies is the absence of recurring fuel costs; and uncertainty of escalation in conventional fuel costs makes these technologies increasingly attractive. In addition, PV has demonstrated low operation and maintenance (O&M) costs as compared to many conventional technologies. It is a solid-state power plant with few moving parts and is the epitome of simplicity in operation, and has the potential for long lifetime if properly cared for. The modular nature of PV can be effectively exploited in building large facilities in stages. PV systems operate silently and environmental effects are minimal, including visual aesthetics. PV systems can be installed rapidly and therefore investment can be delayed until a short period before the predicted load is realized, thus reducing the investment risk. Finally, for mobile and space applications, a high power-to-weight ratio can be realized with PV systems. The primary factors working against the widespread use of PV are its cost (both cell/module cost and the balance of system costs), the need for large collection areas, variability of the output (diurnal and seasonal), and the lack of demonstrated long-term (20-40 years) reliability of some components of the system. The diurnal nature of PV output may require, for some applications, an energy storage system or a back up energy supply such as a battery.