Solar energy can be gained without any restrictions. The solar collectors are the most technologies used to gain heat from solar energy, which can be used in many applications for buildings. as air-conditioning, cooling demand, heating of domestic water. The current work aims to investigate the effect of storage volume and the flow rate of heat transfer fluid on the performance of evacuated tube heat solar pipe collectors. The analysis utilizes the set of observed data for different operating conditions. The storage volume ranged from 4 to 20 l and the working fluid ranged from 0.87 to 1.98 l/min. Experiments were conducted in summer season. Five identical units were used to achieve this work. Each unit consist of three evacuated tubes solar heat pipe, circulating pump, storage tank, valve, pipe connections.