Comparison of solar technologies for driving a desalination system by means of an organic Rankine cycle

In a previous paper the authors analyzed a low power (100 kW) solar organic Rankine cycle (ORC) as the mechanical and thermal energy source for desalination processes. Such a solar ORC is powered by parabolic trough collectors with direct vapor generation (DVG) technology. To this day, however, there are still no commercial implementations of said technology. For this reason, in this paper we analyze a solar ORC configured to use thermal oil as heat transfer fluid (HTF) instead, a technology which may be classified as conventional. As in the previous paper, the analysis is performed with toluene, octamethylcyclotetrasiloxane (D4) and hexamethyldisiloxane (MM) as the working fluids in the ORC. The results obtained indicate that, in a cycle with a recuperator effectiveness of 0.8, it is possible to achieve with LS3 parabolic trough collector overall efficiencies between 20.6%–14% with toluene, 18.3%–11.9% with D4 and 17%–10% with MM for condensation temperatures between 35ºC–115ºC. These values are between 16%–9% for toluene, 14.5%–7.4% for D4 and 14.4%–7.8% for MM if IND300 PTC is used. The condensation temperature range considered is wide enough to analyze the use of the heat rejected by the cycle in a distillation process.