## 2 Drivers of Photovoltaic Technologies
### The Influence of Module Service Life  
When evaluating the service life of a PV system, it is important to consider the system as a whole. The installed PV system can only provide the expected service life if all of its components work properly and the entire PV system is properly serviced, from the PV modules to the high voltage connection. In the case of PV modules, the influence of the environment gradually reduces the efficiency, while the other components may show a fault that affects the function of a  
Figure 6: A schematic projection of module price by (7) in comparison with data [12]. part of the system and can be repaired. Repairs can be included in operating costs, losses associated with failures (and thus with non-energy production), reducing the efficiency of the system. From this point of view, it is possible to approximate the service life of the PV system to the performance guarantee period of the PV modules specified by the manufacturer (only 2% of PV modules are predicted not to meet the manufacturer's warranty after 11-12 years of operation [16] and project life expectations are now even higher than 30 years [17]). This projection of service life is also made possible by the fact that the currently stated service life of inverters is gradually approaching the service life of the modules [18]. The PV system service time, \(n\), also has some influence on the LCOE of photovoltaic systems. In a simple approximation [19], the LCOE can be expressed by  
\[LCOE\approx\frac{IC+nOC_{AV}}{\sum_{1}^{n}EP_{R}}\approx\frac{IC\left(1+\frac {OC_{AV}n}{IC}n\right)}{EP_{1}\times 0,9n}=\frac{IC}{EP_{1}}f(n;\varepsilon), \tag{8}\]  
where \(\varepsilon=\frac{OC_{AV}}{IC}\) and \(EP_{1}\) is the energy produced in the first year of production. Expecting an average irradiance for all years, it is possible to use the following equation as a good approximation:  
\[EP_{1}=Y_{R}P_{STC}\xi(T;G)\eta_{c}, \tag{9}\]  
where \(Y_{R}\) is reference yield, \(P_{STC}\) is nominal power of PV field, \(\xi(T;G)\) is operating condition factor, and \(\eta_{c}\) is DC-AC conversion efficiency. If we assume only the effect of the change in the service life (and other parameters do not change), the relative change in the LCOE when changing the service life from \(n_{1}\) to \(n_{2}\) years can be expressed by  
\[\frac{LCOE(n_{2})-LCOE(n_{1})}{LCOE(n_{1})}=\frac{f(n_{2};\varepsilon)-f(n_{1} ;\varepsilon)}{f(n_{1};\varepsilon)}=\frac{n_{1}-n_{2}}{n_{2}(1+\varepsilon n _{1})}. \tag{10}\]  
Using this approximation, it is relatively easy to quantify advantages following from the module service time prolongation. With a constant investment cost and energy output, the module service life prolongation results in a decrease of the LCOE. In Figure 7, the relative changes of the LCOE caused by an increase in the module service life of 1 year (from \(n\) to \(n+1\)) are plotted as a function of module service life \(n\) (e.g., an increase in the service life from 10 to 11 years results in a relative reduction in the LCOE of 8.26%; an increase in the service life from 20 to 21 years leads to a relative reduction in the LCOE of 3.94%). Comparing Figures 2 and 6, it can be stated that the effect of module life extension on the LCOE is comparable to the effect of increasing the efficiency of modules. Figure 7: The relative changes of the LCOE by 1-year increase in the module service time. When assessing the service life of a PV system, it is important to consider not only the PV module but the system as a whole, from the solar cell to the high-voltage connection. In addition to the influence of module degradation, described by the expected decrease of module efficiency, there may be defects in both modules and other parts of installation, causing random failures in the PV system's operation.