A group out of MIT made an announcement that they are able to harness solar power with a low cost – lower cost than a conventional desal plant – that was able to deliver 6 liters per hour per square meter of collector. Published in the Journal of Energy and Environmental Science, the paper outlines a device that functions as a multi-layer still, using several evaporation and condensation steps to produce water that exceeds current drinking water standards.
As users on a Hacker News thread pointed out – this is a very energy intense process that requires 173 kWh of solar energy, compared to the 3.2 kWh often used for all of the processes in a conventional desal plant like San Diego’s Carlsbad site. The MIT group isn’t radically altering how the current municipal distribution network for drinking water would work – it is instead providing a technology that would allow for a more off-the-grid (“OTG”) approach for desalination, in the same way that generators allow electricity in wilderness cabins. Depending on the setup costs, it’s easy to see a set up where intercoastal waterways and other marshy areas could support units like this that generate reliable small volumes of liquid to support a single household that might not otherwise be able to justify the cost of a desal situation.
Desalination Materials: Ceramic Pressure Exchangers
Looking at how an OTG situation could change how certain areas can create clean water at a lower cost calls back to past technologies that allowed the centralized growth of desalination. Desal occurs at high pressures – this is one of the biggest differences between air and water filtration.
Salt ions are tiny, and even with cross-flow or tangential filtration, it takes very fine pores (~2 nm or less) and high pressure to create potable water from a saline source of water. The energy required to create that pressure was costly and couldn’t be easily recaptured.
The invention of a specialized ceramic pressure exchanger by Richard Stover allowed desalination plants to conserve and recycle that energy, dramatically lowering the cost to create drinkable water.
