The sun radiation is the largest renewable energy source on the planet which can be used in technology by means of thermal, photovoltaic and concentrated solar power systems. In this study, two types of solar collectors, called the "Two Colored Rainbow System", were used as a source for water heating at the Faculty of Science and Letters, at Istanbul Technical University. The performance of solar water heating system was experimentally investigated. In the experimental study, the temperature of hot water storage tank versus time of the day was investigated. The average daily solar radiation at a location is often sufficient for a basic system analysis. The radiation of sun varies according to the location, date, time and conditions of climate. The change of sun radiation was computed using a determined set of parameters. This study was aimed to offer optimization of design parameters taking into account possible interferences during the operation of the system. Additionally, hourly solar radiation on tilted surfaces is measured in Istanbul. Data of solar radiation intensity were also collected using a standard solarimeter (pyrometer) via a data logger.