Portable Distillation Unit Cleans Sea Water on a Sunny Day

A number of solutions have been put forward to address the daunting problem facing roughly a billion people on this planet: a lack of clean, safe drinking water. Climate change is only making the problem worse. Some experts say that 50 percent of the global population will experience some form of water stress by 2030.

A large percentage of these people live near an ocean. Since 97 percent of the world’s water is found in the ocean, it makes sense to use sea water, if possible, as a source that can be purified or desalinated for drinking and cooking purposes. Although desalination tends to be energy-intensive and costly, it has inspired a number of recent improvements.

Among the solutions aimed at this sizable opportunity is a large-scale solar desalination plant in Saudi Arabia, a joint effort between IBM and the King Abdulaziz City for Science and Technology. This approach uses concentrating solar power (CSP) to drive a nano-membrane reverse osmosis system.

Another project in France uses wave power to generate mechanical pumping action that forces seawater through a set of reverse osmosis filters. A smaller, portable solution has been developed by a team at MIT.  This system, which is primarily intended for disaster relief, features a set of solar panels, a water storage tank, a desalination pump and a filtration system.

A new solution was recently announced by Desolenator, a London-based company that launched its first product with a successful $150,000 Indiegogo campaign. Like the MIT product, it too is portable, but it differs from all the systems mentioned above because instead of relying on reverse-osmosis filtration, it purifies dirty water -- including sea water -- by distillation: the simple process of boiling the water and then condensing the steam back into a liquid. While simpler and less reliant on specialized filter materials than RO systems, the need to boil the water requires a great deal of energy.

That’s where there innovation kicks in. While most solar photovoltaic systems try to eliminate heat since it does not contribute to the generation of electricity, the Desolenator captures the heat using insulation, and then uses it to preheat the water to the point where it is nearly boiling. This reduces the amount of energy required to complete the process in a small integrated boiler powered by the solar panels. A single solar-powered unit can provide 15 liters of clean water per day, enough for the drinking and cooking needs of a family of six.

In a sense, it’s a form of combined heat and power (CHP), a technology usually associated with fossil fuel power plants. A few years back I wrote about a couple of other companies, Naked Energy and Cogenra, that combined solar PV and solar thermal, though neither of these used it for desalination.

Inventor and CEO William Janssen told the BBC that the Desolenator can produce desalinated water less expensively than any other option available.

The product has been recognized in various venues, including winning second place in the Climate KIC launchpad (Europe’s largest clean tech business idea competition) and being shortlisted for an Ashoka Award.

The company plans to use the funds raised in the Indiegogo campaign toward a pilot program that will eventually put 1,000 Desolenator units in a village in Tamil Nadu, India -- a next step on the road to scale.

This seems to be a very promising idea, though I do have a couple of caveats. The company's slogan -- "Water independence, just add sun” -- is a bit misleading, since it implies that the unit can simply pull water out of thin air. This is theoretically possible. Dehumidifiers do it, but this device does not. What it does requires an input water source which is then purified using only the power of the sun.

Other minor concerns worth mentioning include the fact that desalination produces distilled water, which is characterized by an absence of minerals often found in naturally occurring water. Experts differ as to the health impact of drinking distilled water. Surely it is better than drinking contaminated water, but over the long term, mineral supplements might be required for optimal health.

Any desalination process will also produce salt as a byproduct. At its rated 15 liter output, the Desolenator is likely to extract approximately one pound of salt per day. By design it maintains the salt as brine to avoid clogging the pipes, cleverly removing additional heat in the process. At some point, though, this brine will need to be removed and responsibly disposed. According to CEO Janssen on this point, "The brine flow (residual salt in seawater) is not an issue in [the] case of the Desolenator technology. The rate of flow of water through the system is relatively high. This means that the salt content of the water coming out of the system is hardly any higher than the seawater going in. Thus the brine water can be disposed of without any objection."

I won’t argue, but it’s probably not something you want to water your vegetable garden with. Better to salt those veggies after they’re cooked.  In an ideal world, I would think, the brine would be returned to the ocean, or upcycled in some constructive way such as adding it to mud to make stronger bricks.

Image courtesy of Desolenator

RP Siegel, PE, is an author, inventor and consultant. He has written for numerous publications ranging from Huffington Post to Mechanical Engineering. He and Roger Saillant co-wrote the successful eco-thriller Vapor Trails. RP, who is a regular contributor to Triple Pundit and Justmeans, sees it as his mission to help articulate and clarify the problems and challenges confronting our planet at this time, as well as the steadily emerging list of proposed solutions. His uniquely combined engineering and humanities background help to bring both global perspective and analytical detail to bear on the questions at hand. RP recently returned from Abu Dhabi where he attended the World Future Energy Summit as the winner of the Abu Dhabi blogging competition.

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