## 3 Results
### Intra-Annual Energy Yields  
Section 3.1 demonstrated that the optimum tilt angle for the maximum annual solar energy received on an inclined plane in Greece is either 25\({}^{\circ}\) or 30\({}^{\circ}\) to the south. Apart from the annual energy yield, a solar energy investor is also concerned about the monthly solar energy availability at the site of interest. Therefore, the analysis in the present section is concentrated on the monthly energy received by flat planes with inclinations of 25\({}^{\circ}\) S or 30\({}^{\circ}\) S without discrimination. For this reason, Figure 6 has been prepared to show the intra-annual variation of the total energy yield from solar convertors inclined at 25\({}^{\circ}\) or 30\({}^{\circ}\) to the south at all 33 sites. It is seen that the variation was limited between a low of 50 kWhm\({}^{-2}\cdot\)month\({}^{-1}\) and a high of 250 kWhm\({}^{-2}\cdot\)month\({}^{-1}\). The graph is not intended to show the intra-annual variation of individual sites, but rather its variation as an ensemble. \begin{table}
\begin{tabular}{c c c c} \hline
**Site** & **PV\({}_{0}\) Zone** & **PV\({}_{\text{cts}}\) Zone** & **Optimum \(\beta\) (Degrees S)** \\ \hline \hline \multicolumn{1}{c}{Agrinio} & B & A & 30 \\ \hline \multicolumn{1}{c}{Alexandroupoli} & D & D & 30 \\ \hline \hline \multicolumn{1}{c}{Anchialos} & C & C & 30 \\ \hline \hline \multicolumn{1}{c}{Andravida} & B & A & 30 \\ \hline \hline \multicolumn{1}{c}{Aravas} & B & A & 30 \\ \hline \hline \multicolumn{1}{c}{Chios} & C & C & 25 \\ \hline \hline \multicolumn{1}{c}{Elliniko} & B & A & 25 \\ \hline \hline \multicolumn{1}{c}{Ioannina} & D & D & 30 \\ \hline \hline \multicolumn{1}{c}{Irakleio} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Kalamata} & B & A & 30 \\ \hline \hline \multicolumn{1}{c}{Kasteli} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Kastoria} & C & C & 30 \\ \hline \hline \multicolumn{1}{c}{Kerkyra} & D & D & 25 \\ \hline \hline \multicolumn{1}{c}{Kozani} & C & B & 30 \\ \hline \hline \multicolumn{1}{c}{Kythira} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Lamia} & C & C & 25 \\ \hline \hline \multicolumn{1}{c}{Larsa} & C & D & 25 \\ \hline \hline \multicolumn{1}{c}{Lesvos} & B & B & 30 \\ \hline \hline \multicolumn{1}{c}{Limnos} & C & C & 25 \\ \hline \hline \multicolumn{1}{c}{Methoni} & B & B & 25 \\ \hline \hline \multicolumn{1}{c}{Mikra} & D & D & 25 \\ \hline \hline \multicolumn{1}{c}{Naxos} & B & A & 25 \\ \hline \hline \multicolumn{1}{c}{Rodos} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Samos} & B & B & 25 \\ \hline \hline \multicolumn{1}{c}{Serres} & D & D & 30 \\ \hline \hline \multicolumn{1}{c}{Siteia} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Skyros} & D & D & 25 \\ \hline \hline \multicolumn{1}{c}{Souda} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Spata} & B & B & 25 \\ \hline \hline \multicolumn{1}{c}{Tanagra} & B & B & 25 \\ \hline \hline \multicolumn{1}{c}{Thira} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Tripoli} & A & A & 25 \\ \hline \hline \multicolumn{1}{c}{Zakynthos} & B & A & 30 \\ \hline \end{tabular}
\end{table} 
Table 5: Classification of the 33 sites in terms of the PV\({}_{0}\) and PV\({}_{\text{cts}}\) zones, together with the optimum inclination angle \(\beta\) to the south of the solar flat-plane convertors operating in Greece for a whole year. It is worth observing that only one-third of the sites utilize \(\beta=30^{\circ}\). The gray rows denote a change of the site’s categorization from the PV\({}_{0}\) zone in Table 3 (see also Figure 3b) to the PV\({}_{\text{cts}}\) scheme in Figure 5b. To demonstrate the intra-annual variation of \(G_{e,\beta S}\) or \(G_{e,30S}\) in each specific PV\({}_{\rm ctts}\) zone, Figure 7 was produced.