Don’t Give up on Desalination

desert and stars

How we manage local water sources drastically alters how we grow crops and get drinking water. Cape Town is currently experience a water crisis that was in the making for decades because of poor water use policies. Desalination plants can help coastal cities provide water to their populace by separating salt from seawater. Wired has a good article on how one company is improving desalination techniques for growing crops, which, they predict can help bring plant life to arid regions.

The structure’s double-layered fibreglass roof transmitted sunlight but captured heat, diverting it through ducts into a compartment at the building’s rear. There, the heat was used to distill freshwater out of seawater for irrigation. The rest was vaporised and sucked through the growing space by fans to cool and humidify the plants, reducing transpiration. Paton calculated that a square metre of crops adjacent to the greenhouse would have required eight litres of water per day to offset what they lost in transpiration. “But inside we were using closer to one litre per square metre per day, and we were growing a better crop.”

Paton is also interested in the long term restorative benefits of his invention. Davies’ model predicted that the greenhouse’s cooling and humidifying effect would seep into the surrounding environment: “You can see there would be a plume of cool air coming off the greenhouse,” he says. And since the region hasn’t always been barren, Paton thinks greenhouses could return parts of it to the naturally vegetated state it was in before overgrazing and drought took hold. “I believe that when you get to, say, 20 years, you’d have enough vegetation to do the job of the greenhouses because they’re creating shade and shared humidity – changing the climate.” Because vegetation sequesters carbon, that also has broader ramifications for mitigating the effects of climate change.

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Using Seawater to Farm in the Desert

The future of farming in much of the world could look like something out of science fiction. Sundrop farms in Australia has a farm up and running that produces food using seawater pumped into a desert location where they use the power of the sun to power the entire process. Solar energy desalinates the water while purifying the environment (so no pesticides) of the greenhouse – the entire process is form renewable sources!

Seawater is piped 2 kilometres from the Spencer Gulf to Sundrop Farm – the 20-hectare site in the arid Port Augusta region. A solar-powered desalination plant removes the salt, creating enough fresh water to irrigate 180,000 tomato plants inside the greenhouse.

Scorching summer temperatures and dry conditions make the region unsuitable for conventional farming, but the greenhouse is lined with seawater-soaked cardboard to keep the plants cool enough to stay healthy. In winter, solar heating keeps the greenhouse warm.

There is no need for pesticides as seawater cleans and sterilises the air, and plants grow in coconut husks instead of soil.

The farm’s solar power is generated by 23,000 mirrors that reflect sunlight towards a 115-metre high receiver tower. On a sunny day, up to 39 megawatts of energy can be produced – enough to power the desalination plant and supply the greenhouse’s electricity needs.

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Wave Energy for Desalination

CETO Wave Energy has designed a system that uses tidal power to both pump water and desalinate it! Desalination is a growing necessity in areas lacking fresh water that have access to sea water; however, it is energy and cost intensive. By using a renewable resource, it makes desalination a viable option.

Unlike other wave energy systems currently under development around the world, the CETO wave power converter is the first unit to be fully-submerged and to produce high pressure seawater from the power of waves.
By delivering high pressure seawater ashore, the technology allows either zero-emission electricity to be produced (similar to hydroelectricity) or zero-emission freshwater (utilising standard reverse osmosis desalination technology). It also means that there is no need for undersea grids or high voltage transmission nor costly marine qualified plants.

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