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This paper presents the technical characteristics as well as an economic comparison of two autonomous desalination systems. The first system concerns the laboratory experimental results of a direct coupled PV-SWRO desalination system without batteries equipped with a hydraulic energy recovery device of the Clark pump type. The PV system consists of 18 Arco-Solar monocristaline PV panels, with total peak power of 846 W. These panels are directly connected to a brushless DC motor of 510 W, powering a rotary vane pump as low pressure pump. The clark pump utilizes the high pressure brine to intensify the feed pressure to the RO desalination system. The desalination system has a capacity of 0.1 m3/h. The specific energy recovery of this system has been experimentally found to be in the range of 3.8–6 kWh/m3 depending on the feed water temperature and the feed water salinity. The second system is an organic solar Rankine system for RO desalination. The heat produced by the solar collectors’ field is transformed to mechanical power through an organic Rankine cycle process. The shaft power produced drives the high pressure pump of the RO unit, initiating the desalination process. The prototype system consists of vacuum tube solar collectors 90 m2, a Rankine engine of 100 kW and an RO unit of 0.3 m3/h. The energy recovery system of the RO unit consists of a pair of axial piston pumps (APP) manufactured by Danfoss. One of them operates reversely, as turbine, exploiting the hydraulic energy of the brine stream. The aim of the economic analysis is not only to estimate the cost of each system but also to compare them on the same basis, in order to allow a meaningful comparison. Hence, each system cost is determined having utilised the same economic assumptions like interest, operating expenses, etc. Moreover, these desalination systems can provide

There is an increasing need for renewable energy powered desalination systems as this seems to be the sole environmental friendly alternative to the conventional fossil fuel powered systems. RO seems to be particularly suitable for combining either direct electricity producing technologies (such as PV and wind turbines) or indirect such as solar collectors. The cost of desalination using the PV-RO system is 7.77 h/m3 while that of the RO-Solar Rankine system is as high as 12.53 h/m3, mainly due to the more innovative, but expensive energy source that uses. Yet, the cost of the solar organic Rankine cycle can be significantly reduced after commercialization as it is estimated that a 30% reduction of cost can be achieved in the commercial product. The cost of both systems can decrease dramatically if we use conventional sources of energy.