# Geographical Distribution of Global Radiation and Sunshine Duration over the Island of Cyprus
## 4 Conclusions
A detail quality control procedure was implemented on the radiation components, which are based on the suggested limits proposed by the BSRN group. The tests include physically possible limits (PPL) and extremely rare limits (ERL). Additionally, the data were tested according to the values of the clearness index of \(\mathrm{k_{t}}\), which is always lower than 1. Finally, step and persistency tests were applied on the hourly dataset. The daily values were also tested against the extraterrestrial irradiation and the estimated highest daily sums on clear days as well as by comparing the daily global radiation with the daily sunshine duration. Generally, all data are within the specified limits. However, the data of two stations (Lefkara Dam and Zygi) were excluded from the analysis because most of the data were outside the PPL and ERL limits, either due to problems of wrong installation or to the presence of trees in the surrounding area, which thus affected the incidence of global irradiance. The statistical analysis was demonstrated mainly through the graphs of boxplots, where the basic statistics of each location are presented and, at the same time, the stations can be compared on a monthly basis. From this investigation, the following results can be highlighted:  
Monthly mean daily values of global irradiation either measured or estimated from the daily sunshine duration are shown by means of isolines diagrams. These values are considered representative of the solar radiation behavior along a typical year and can be useful for exploiting solar energy applications. Seasonal analysis allows the highlighting of the differences between summer and winter irradiation conditions. June and July were found to be the months with the highest values of mean daily global radiation. During these months, daily global irradiation ranged between 25 MJ/m\({}^{2}\) and 30 MJ/m\({}^{2}\), with the lowest occurring in the mountainous locations. On the other hand, in January or December, they ranged between 6.5 MJ/m\({}^{2}\) and 10.5 MJ/m\({}^{2}\). Regarding the annual variation of the mean daily global irradiation, it is shown that it ranged between 16 MJ/m\({}^{2}\) and 20 MJ/m\({}^{2}\). The maximum of daily global solar horizontal irradiation was reached in June or July and it was almost 32 MJ/m\({}^{2}\). The annual daily average of sunshine duration ranged between 7.0 h and 9.5 h with the lowest values occurring in the mountainous locations. The monthly mean daily values ranged between 3 and 6.5 h in January, while they ranged between 10 and 13.5 h in June or July. The maximum daily value was almost 14 h and it occurred in the summer months. The total annual number of hours of sunshine duration ranged between 2500 and 3500, with the lowest values recorded at the mountainous sites. The monthly mean daily relative sunshine duration in the coastal and inland plain locations ranged between 0.5 in January and 0.9 in July. Slightly lower values were recorded in the mountainous sites. Linear relationships were established between the daily clearness index (\(K_{T}\)) and the daily relative sunshine duration (\(\sigma\)), while quadratic relationships were established between the daily global radiation (\(G_{d}\)) and the daily sunshine duration (\(S_{d}\)). Both equations are associated with high coefficients of determination. In the case of the linear equations (\(K_{T}\) vs. \(\sigma\)), the intercept ranged between 0.100 and 0.280, while the slope ranged between 0.455 and 0.700. The sum of the intercept and the slope indicates the amount of global radiation reaching the ground on a clear day. The average sum of the constants of all the sites was 0.788. Generally, the coastal and inland plain stations showed higher \(K_{T}\) values than the mountainous sites, throughout the year. The annual average of \(K_{T}\) of the first group was 0.617 and the second group was 0.583.