Fluid Notes: Solar Power, Ceramic Pressure Exchangers and the Cost of Desalination

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.

Energy Recovery Inc’s (“ERI”) ceramic pressure exchanger made a major impact on the energy requirements to create drinking water using desalination.

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