Abstract Photovoltaic powered brackish water reverse osmosis (PV-BWRO) desalination systems have been proved to be a technically and economically mature choice for water supply in isolated communities and islands suffering from lack or poor water quality. However, photovoltaic seawater reverse osmosis (PV-SWRO) systems are characterized for their high water production cost that reaches the value of 15–20 Є/m 3. This high water production cost is mainly due to the high energy requirements (10–20 kWh/m 3) that accounts for around 60–70% of the operating and maintenance cost and that is due to the fact that majority of the small autonomous PV-SWRO do not contain energy recovery devices (ERDs). Another reason for the high water production cost is the need of solar batteries to achieve a constant pressure and flow rate for the membranes. Solar batteries are characterized by their high capital cost that reaches 110 Є/kWh and operating cost mainly due to the replacement cost, solar batteries also have short operation life especially in hot climates. In this work a batteryless PV-SWRO equipped with an ERD is installed, tested and compared to a battery based system, promising to produce 0.35 m 3/d in winter (feed water temperature 18°C) consuming only 4.6 kWh/m 3 with a cost of 7.8 Є/m 3.