Spraying pesticides are important to protect crops from insects consequently to obtain the highest production yield. The manual or battery knapsack sprayers are dominant in the Egyptian market. However, the first type depends on the operator skill and for the second type; the battery charge is not constant throughout the operating period. Therefore, the research aimed to develop a knapsack sprayer powered by solar energy that operates throughout the day at constant flow rate pressure. This was achieved by manufacturing the developed sprayer from local materials, and by providing it with a solar pump powered by a battery, the photovoltaic panel and an electronic circuit in which the spray pressure can be controlled from 0 to 4 bars. The amount of pesticide can be controlled according to the age of the plant, as well as, the uniformity of pesticide distribution identified using constant pressure throughout the spray period and thus ensuring the fairness of pesticide distribution and not relying on lobar experience. The results indicated that the number of operating hours for the developed sprayer reaches more than 8 hours per day with constant pressure compared to using the battery-powered sprayer only, which operates from 1.5 to 3 hours only with no pressure stability at a flow rate 600 to 1000 ml/min. On the economic side, the cost of spraying from the developed sprayer is 54.37 L.E/fed compared with (102.50 and 79.70 LE /fed) for manually sprayer and battery sprayer, respectively. Therefore, a developed sprayer is high economic and practical value in the agricultural sector.