Recently, thermosiphon has been considered as an economically competitive approach for the withdrawal of thermal energy from molten salt. This feature of thermosiphon is particularly attractive for concentrated solar power (CSP) technology because molten salt can be used both as the direct receiver and thermal energy storage material, and pumping requirements can be minimized. However, the thermosiphon loop must be properly designed; otherwise the heated molten salt can flow in the reverse direction or solidify before heat exchange is fully carried out. In this paper, the dependence of important molten salt flow characteristics such as temperature, velocity and friction factor on the thermosiphon loop dimensions is theoretically investigated. The model is carried out for the withdrawal of 1 MW of thermal energy from the molten salt. The economic assessment of the conversion of this energy to electricity for reverse osmosis desalination is also carried out. It is observed that by using the minimum possible value of leg length and maximum possible values of diameter and pressure head, the lowest decline of temperature and highest velocity of flow can be achieved along the loop. Fresh water production is more valuable than electricity and steam production by 460% and 480%, respectively.