The Potential of Using Solar Energy in Operating Irrigation Surface Pumps El-Quosy, D. A. 1 ; Mohamed, M. A. 2 ; Aboamera, M. A 3 and Abou Khiera, A. A .4 ABSTRACT The objective of this study was to derive the hydraulic performance indicators, which are, discharge, pressure and efficiency for solar surface pump operated by solar energy in lifting water. The study included different levels of the factors affecting the pump performance that are tilt angle, solar cells area and cleaning degree of solar cells. Cost analysis has been carried out for estimating the required unit water cost and comparing it with its values for both of electrical and diesel pumps. The Highest values of pressure (13x104 N/m 2 ), discharge (9.02 m 3 /h) and efficiency (36.72%) were achieved at 30 ϩ of tilt angle and 40 m 2 of solar cells area. Increasing cleaning degree of the solar cells by 100% leads to increase the daily yield of solar surface pump by 31.5%. The unit cost of lifted water by solar surface pump is 0.17 L.E./m 3 compared with 0.04 L.E./m 3 and 0.03 L.E/m 3 for diesel and electrical surface pumps respectively. Using of photovoltaic array for solar pump doesn't depend only upon the unit water cost but also upon many other conditions. In case of non-availability of diesel or electrical power, the high cost of solar pumps must not be taken into account. It can be concluded that improving the solar pumping system must be focused on minimizing the unit water cost in order to use it in a large scale. The photovoltaic array takes the first place as the best cleaning energy comparing with the sources of chemical energy. ___________________________________________________________________________ (1) Prof. Dr., National Water Research Center (2) Associate Prof., Ag. Eng. Minoufiya University (3) Lecturer, Ag. Eng. Minoufiya University (4) Assistant Researcher, Water Management and Irrigation Systems Research Institute, National Water Research Center.