There are several ways to predict and/or estimate solar radiation in a particular defined area. It is important to model and design the efficiency of solar systems such as time series, solar radiation data. The time series data are significant for performance prediction and other purposes. The solar radiation data which belong to the defined location are not always available. In this study, it is investigated that how affected hourly solar radiation value under conditions of cloudiness. The methods in the literature are based on a decomposition model that calculates solar radiation components related to atmospheric transmittance. This study aims to evaluate the hourly irradiance by added effect of cloudiness on calculations for Turkey. While a decision matrix was used in several methods, the regression correlation of meteorological parameters was used in the other methods. In addition, the API application program is created by Java programming language. This enables users to obtain solar radiation for getting data, processing, extracting meaningful result and making these processes respectively where they are. The results show that the climate variables, air temperature, and solar radiation were highly correlated to transpiration.