# Geographical Distribution of Global Radiation and Sunshine Duration over the Island of Cyprus
## 4 Conclusions
The average values of the daily clearness index ranged between 0.495 in January and 0.685 in July for the first group, while they ranged between 0.445 in January and 0.668 in July for the second group of the stations. A linear relationship between the annual mean \(K_{T}\) and elevation showed the decrease in the annual mean \(K_{T}\) with elevation. The average global irradiation was almost similar in both groups of stations. The annual average of global irradiation was about 7 MJ/m\({}^{2}\) on cloudy days and about 21 MJ/m\({}^{2}\) on clear days. However, the annual number of cloudy days was 21 (about 6%) for the first group and almost twice (39) for the second group, representing 11% of the annual number of days. The respective number for partially cloudy days was 121 and 149 days, while the days that are classified as clear days were 208 (57%) and 166 (45%), respectively. As can be seen, the summer months were classified mainly as clear days. The monthly average frequency of days according to their type gives an initial indication of the relative viability of different solar collector types. For example, concentrating solar collectors operate best under clear day conditions and to a much lesser extent, under partially cloudy days. The major difference between day types was the significant reduction in the beam radiation, which also affects the global irradiation level. Regarding the global radiation, the reduction factor for partially cloudy days to that on clear days ranged from 0.73 to 0.78. The monthly means of hourly clearness indices (\(k_{i}\)) ranged mainly between 0.5 and 0.65 with the highest occurring in summer. Slightly lower values were observed at the mountainous sites (0.4 to 0.6). During clear-sky conditions, global irradiances ranged between 500 and 750 W/m\({}^{2}\), while during partially cloudy conditions they ranged between 200 and 400 W/m\({}^{2}\). In contrast, they ranged between 100 and 200 W/m\({}^{2}\) during cloudy conditions. However, at the mountainous sites, they were slightly higher than 100 W/m\({}^{2}\) during overcast conditions throughout the year. Regarding the case of all sky conditions, they ranged mainly between 250 and 550 W/m\({}^{2}\). Regarding the duration of the annual hours of the stations during overcast skies (DOS), they ranged between 296 and 1479 h, for intermediate skies (DIS) they ranged between 789 and 1901 h, while for clear skies (DCS) they ranged between 1075 and 2359 h. The average values for the three types of skies were 840.7 \(\pm\) 368.4 h, 1239.7 \(\pm\) 276.6 h, and 1819.8 \(\pm\) 323.2 h, respectively. These results show that the intermediate and clear sky conditions over Cyprus prevailed throughout the year, while overcast conditions were more frequently expected in the mountainous areas. This work has specifically contributed to the characterization and analysis of hourly and daily solar global radiation. Furthermore, the measurements on the ground level could be compared with satellite observations in order to improve the geographical distribution of global radiation, especially in areas where no measurements exist. The analysis could be also extended for the other shortwave radiation components (Direct, Diffuse and Photosynthetic Active Radiation (PAR)) in order to assess the solar radiation regime over the island. The results of this paper are of the utmost importance to scientists and engineering working in the field of solar energy, which includes both solar thermal collectors and systems and photovoltaic systems. The input power to these systems is solar radiation, and therefore knowing this with some accuracy is very important. With the knowledge of global solar radiation on horizontal surfaces, we can estimate the solar radiation on inclined surfaces [8], and therefore we can assess more accurately the efficiency of photovoltaic systems. Methodology, S.P. ; Investigation, S.P. ; Resources, A.P. ; Supervision, S.A.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding.