This paper deals with innovative renewable energy (RE) - powered seawater reverse osmosis (SWRO) plants based on tidal range/PhotoVoltaic (PV) systems as a hybrid technology with interesting prospects to promote the RE desalination at medium to large capacity ranges. Key features to enhance solar PV with tidal range energy are the good temporary complementarity of both options and the predictable water production pattern that the tidal range plant allows, along with ensuring water production at night. Once the basic sizing of a power plant referred to a 20 MW turbine is conducted, the sensitivity analysis of main performance parameters of the hybrid solar/tidal desalination system is carried out through yearly simulations. With this analysis, an extension of the knowledge about the performance of hybrid tidal/solar desalination is gained in such a way that three useful design criteria are derived from the results: i) total investment cost per unitary water production, ii) energy consumed in desalination to total energy production, and iii) energy non-useful for desalination. Recommended designs are provided under each of these three criteria for given yearly freshwater demand with SWRO plants of 3.5 and 4.8 kWh/m3 of specific energy consumption. Results proves that off-grid SWRO desalination powered by hybrid tidal/PV systems in a favorable location achieves actual water production of one half of nominal production with adequate selection of design parameters. Recommended sizing of the energy generator for minimizing capital costs corresponds to 20 MW tidal/25–27 MWp PV per 12 MW of SWRO consumption. Additionally, in absence of realistic costs data, the recommended design criterion for the plant sizing relies on the ratio of energy used by the desalination plant to that produced by the hybrid tidal/PV generator. Results at an exemplary plant location show that 14.1 × 106 m3/y of fresh water obtained with desalination consumption of 3.5 kWh/m3 needs 2.0 MW tidal/26.9 MWp PV. This energy system would produce 10 × 106 m3/y considering 4.8 kWh/m3 of specific consumption.