## 3 Results
### Annual Energy Yields
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**\# *} & **Site** & **WHO Code ** & \multicolumn{3}{c}{**Categorization Scheme**} \\ \cline{3-5}  & **(Region of)** & \(\varphi\)/\(\lambda\)/z *** & **Climatic Zone** & **TOTEE Zone** & **PV\({}_{0}\) Zone** \\ \hline
24 &
\begin{tabular}{c} Navos \\ (Southern Aegean) \\ \end{tabular} & 16732 & A & A & B \\ \hline
30 &
\begin{tabular}{c} Rodos \\ (known as Rhodes, Southern \\ Aegean) \\ \end{tabular} & 16749 & A & A & A \\ \hline
22 &
\begin{tabular}{c} Samos \\ (Northern Aegean) \\ \end{tabular} & 16723 & A & A & B \\ \hline
1 &
\begin{tabular}{c} Serres \\ (Central Macedonia) \\ \end{tabular} & 41.083/23.567/34.5 & D & B/C & D \\ \hline
32 &
\begin{tabular}{c} Siteia \\ (Crete) \\ \end{tabular} & 16757 & A & A & A \\ \hline
15 &
\begin{tabular}{c} Skyros \\ (Sterea Ellada) \\ \end{tabular} & 38.924.55/17.9 & B & B/C & D \\ \hline
29 &
\begin{tabular}{c} Souda \\ (Crete) \\ \end{tabular} & 16746 & A & A & A \\ \hline
26 &
\begin{tabular}{c} Spata \\ (Attica) \\ \end{tabular} & 16741 & B & A & B \\ \hline
17 &
\begin{tabular}{c} Tanagra \\ (Sterea Ellada) \\ \end{tabular} & 16699 & B & A & B \\ \hline
28 & \
\begin{tabular}{c} Shrira \\ (known as Santorini, \\ Southern Aegean) \\ \end{tabular} &
\begin{tabular}{c} 16744 \\ 36.417/25.433/36.5 \\ \end{tabular} & A & A & A \\ \hline
19 &
\begin{tabular}{c} Tripoli \\ (Peloponnese) \\ \end{tabular} & 16710 & C & A & A \\ \hline
21 &
\begin{tabular}{c} Zakynthos \\ (known as Zante, \\ Ionian Islands) \\ \end{tabular} & 16719 & A & A & B \\ \hline \hline \multicolumn{5}{l}{* number of the site used in the map of Figure 1. ** World Meteorological Organization station’s code. *** Geographical latitude (degrees N)/ geographical longitude (degrees E)/altitude (m amsl).} \\ \end{tabular}
\end{table} 
Table 3: _Cont._that the energy received per tilt angle was at its maximum at 25\({}^{\circ}\) or 30\({}^{\circ}\) in all PV\({}_{0}\) zones, as demonstrated in Figure 4; the energy received on the horizontal plane is shown at \(\beta=0^{\circ}\). In order to discriminate the sites according to the energy received on a south-facing flat-plate solar convertor in Greece tilted at either 25\({}^{\circ}\) or 30\({}^{\circ}\), three thresholds were introduced for this purpose: 1900 kWhm\({}^{-2}\cdot\)year\({}^{-1}\), 1850 kWhm\({}^{-2}\cdot\)year\({}^{-1}\), and 1800 kWhm\({}^{-2}\cdot\)year\({}^{-1}\)). These diving lines formed four new zones, which are called PV\({}_{\text{ctts}}\) zones (ctts = constant tilt to the south). By picking the optimal tilt angle for each site for the maximum annual energy received on a solar panel with an inclination to the south, Figure 5b was drawn. It shows all 33 sites, with the annual energy received on a sloped surface with an inclination of either 25\({}^{\circ}\) or 30\({}^{\circ}\). The color of each data point in Figure 5a,b refers to the PV\({}_{0}\) zone it belongs to (red for PV\({}_{0}\)-zone A, orange for PV\({}_{0}\)-zone B, green for PV\({}_{0}\)-zone C, and blue for PV\({}_{0}\)-zone D). Table 4 summarizes the thresholds for the PV\({}_{\text{ctts}}\) (inclined surfaces), PV\({}_{0}\), and TOTEE (horizontal plane) classification schemes. Because of the above findings, Table 3 can be modified to Table 5 to include the optimal tilt angle per site. Figure 4: Solar energy yield per year \(G_{e,pS}\) on the planes with tilt angles to the south in the range of 5–60\({}^{\circ}\) in steps of 5\({}^{\circ}\) at four representative sites in Greece. The maximum energy received per year in each site is presented by squares, and the energy received at tilt angles equal to \(\varphi^{\circ}\) is shown by triangles. The energy received by a horizontal flat plane (\(\beta=0^{\circ}\)) is also shown. Figure 5: (**a**) Solar energy yield per year on a south-facing plane with an inclination of 0–60\({}^{\circ}\) in steps of 5\({}^{\circ}\). The inclination of the averaged \(\varphi^{\circ}\) is presented with triangles.