Strategies to Enhance Performance of Solar Driven Desalination
Dongare, Pratiksha Digambarsing
Halas, Naomi J
Doctor of Philosophy
Solar-driven evaporation-based distillation processes provide a promising solution to meet the increasing global fresh water need by purifying alternative high salinity sources like seawater and brackish reservoirs. With more than a billion people around the world lacking access to clean water and electricity, it becomes important to develop solutions capable of completely off-the-grid operation. Given the amount of sunlight incident at a given location per unit area per unit time, it becomes crucial to utilize the available photons as effectively as possible to maximize the clean water production. In our recent work, we demonstrate that photon flux redistribution, by focusing incident sunlight with lens arrays into small “hot-spots”, on top of a photothermal membrane dramatically increases – by more than 50% - the flux of distilled water. This large boost in efficiency results from the nearly exponential dependence of water vapor saturation pressure on temperature, and therefore on incident light intensity. We also demonstrate that the energy used for phase change in distillation can be recovered from the distilled water to preheat the input water and matching the feed and distillate flows achieves a resonance condition in heat transfer. The purified water production is maximized at the resonance condition and can be optimized for a given system size, system losses and incident light intensity. Exploiting the inherent but previously unrecognized optical nonlinearity and resonant heat recovery should enable the design of substantially higher-throughput solar thermal desalination methods. These mechanisms are capable of enhancing a far wider range of photothermally driven processes as light-driven chemical reactions, separation methods, and thermal energy storage.
Solar; Photothermal; Desalination; Nanophotonics