There has been a great concern about shortage of potable water in many countries as well as Iran, because of the dramatic low rainfall during past few decades almost in all over the Iran. There is a great concern for implementing renewable desalination systems as it seems to be the only clean and environmental friendly source to the traditional fossil fuel powered systems. This study sought to simultaneously assess the reliability of electricity and cost in off grid photovoltaic systems for a photovoltaic reverse osmosis desalination system in 9 districts of Bushehr Province in Iran. Solar data used in this study contains indices of "Clearness Index" and "Daily Solar Radiation" over a period of 16 years from 2000 to 2016. HOMER and Excel were used for technical-economic feasibility of the proposed systems. For this study, a new model of BWRO-2S-130/75 desalination system is tested and proposed. The results indicate that the proposed photovoltaic systems are technically and economically feasible. It was also found that the reliability of off grid photovoltaic system using fuzzy time function provided better results than using the simple method. The results of the evaluation of proposed photovoltaic systems by HOMER software shows that annual electricity production for Delvar and Deylam port are 72,336 and 47,915 kWh respectively which is promising. Also, maximum of 228 m(3) and a minimum of 148 m(3)/day of potable water can be produced with cost of 1.96 to 3.02 $/m(2) for Delvar and Deylam port respectively. Results indicate that using the proposed system of desalination would be economically feasible for Delvar, since the predicted water cost is cheaper compared to existing water price of $2.5. The new model of BWRO-2S-130/75 desalination can meet the water demand of the selected city.