Due to the promising technical feasibility of PV powered RO unit, many studies worldwide are carried out to further enhance their performance. In this simulation studies, we investigate the performance and efficiency of a battery free portable PV-RO unit powered directly and continuously from the PV array and compare it to the performance of a solar battery driven RO unit. The solar battery is charged during daytime using the PV array and runs the RO setup during nighttime. However, the energy provided by the PV array is intermittent and depends on daily available irradiations. Fortunately, in the case of the battery less unit the energy consumption of the RO unit can be adjusted by manipulating the brine flow rate or/and system pressure. In this work, we discuss two techniques for automatic adjustment of RO parameter (e.g. valve position at the brine) so that RO power consumption matches the maximum power provided by PV arrays. Matlab/Simulink implementations performed in these studies are presented and simulation results of battery less PV-RO system driven by UM and solar battery driven RO system are presented and compared. © 2019 IEEE.