According to Charlie Paton and his company SeaWater Greenhouse, the technology produces more freshwater than the plants in the greenhouse need. In fact, you could almost turn the function of the greenhouse on its head - it could primarily become a desalination plant that beats existing technologies on cost effectiveness and produces vegetables as a bonus.
Given that the recent World Water Forum in Japan concluded that a) there isn't enough freshwater, and b) that this will be a major problem, we wondered whether nanotechnology could help Charlie's greenhouses.
Nanotechnology is already producing stronger steels and concrete, so an initial thought was that it could be applied here. But the strength of the support structure is not an issue, so no luck there. Ditto on new aerogels.
What about the "glass" of the greenhouse? Nanotechnology offers smart coatings that are self-cleaning, can change colour on demand, or even produce electricity. One of Charlie's main problems came up here. The greenhouses are constructed using polythene: this is cheap but degrades quite rapidly when exposed to ultraviolet (UV) light. There are alternatives, but they are very expensive. One of the most publicized applications of nanotechnology is a new generation of sun screens based on zinc or titanium oxide. These keep out damaging UV while remaining transparent to other frequencies - a function of the nanoscale dimensions of the particles. Suppose you could produce a coating of such nanoparticles that could be sprayed on? Now there's a thought.
As for the polythene itself, might the new generation of nanoclay composites, which are being applied to food packaging and beer bottles, make for stronger and longer lasting "glass" for the greenhouses?
Then there's the matter of keeping out certain frequencies of light - the infrared that produces unwanted heat, for example - while letting others in. Patterns with sub-wavelength structures can do this. But is there an approach that could economically produce such material on a large scale? Well yes, the growing field of nanoprinting or soft lithography. This encompasses a variety of highly scalable, potentially simple and thus cheap approaches that can create nanoscale features. Another possibility.
What about the generation of electricity from solar energy, an area where nanotechnology holds great promise? The basic greenhouse design is planned to ultimately require no external power input, but adding some into the equation brings the possibility of more applications. Since many of the ideal sites for such greenhouses are not close to a grid system, efficient local power generation may indeed be an asset.
Already there seem to be many areas in which nanotechnology may be able to help out in the near future. There are more esoteric crossovers too, such as the deposition of calcium on the cardboard evaporators. Soft materials such as calcium carbonate (basically chalk) can create remarkably strong materials when built from the bottom up with a nanoscale structure. Take mother of pearl, for example. There is a lot of research in this area, part of the field of biomimetics. Might the cardboard evaporators prove to be a useful construction material when they come to the end of their working lives?
What will come of these discussions remains to be seen, but this story illustrates the variety of ways that nanotechnology might impact a particular application right now. In some cases, and this may be one, it could tip the scales just enough to turn an interesting experiment into an ecologically sound boon for resource-limited countries, and a global business to boot.