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How Uneconomic Would It Be To Produce Fresh Water From Sea Water Using Solar Power?

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sandyRoe | 11:55 Fri 11th Sep 2020 | Science
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Countries like Australia and Saudi Arabia, for example, have coastlines and lots of sunshine. The costs involved must be prohibitive or they'd be doing it.

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I don't know the answer but can state with some authority, the Perth, P&K has no need of this witchcraft. :-)
14:16 Fri 11th Sep 2020
// it is expensive because large amounts of thermal energy are needed to heat the seawater.//
I don't know enough about how this would work to comment in too much detail, so the best I can do for the time being is refer you to the wiki article below:

https://en.wikipedia.org/wiki/Desalination

Best I can tell, it *is* adopted in many of the places you mention, but it's not yet efficient or economical enough to be a main supply of fresh water.
Loads of countries who enjoy sunshine and hot weather do have de-salienation plants. Malta often suffers water shortages when their underground cisterns start emptying. They have a desalination plant in Marsasloxx Bay. How do you know a lot of these plants do not harness solar energy to operate them?
It would be low cost according to this report:-
https://www.sciencedaily.com/releases/2019/01/190107131242.htm
well it takes lecky to desalinate and if the country concerned has a lot of the old current bun then solar is a good way to produce it but the cost benefit equation is a complex one that is dependent on the exact conditions available.
if globally, we are using too much water, then taking it out of the sea is only a short term solution..and one that will only be economical coastally
// it is expensive because large amounts of thermal energy are needed to heat the seawater.//

It is not necessary to heat the seawater, danny. There are thousands of desalination plants around the world and most of them use the "reverse osmosis" principle. This is effectively a sophisticated "straining" system and very little energy is needed:

https://en.wikipedia.org/wiki/Reverse_osmosis

There is one on the river Thames in East London:

https://londonist.com/2015/10/london-s-desalination-plant
About half of the water supplied to Perth, WA comes from desalination. (Source: https://www.watercorporation.com.au/Our-water/Desalination )

It takes 3.5kWh of energy to desalinate 1 cubic metre of water at the Perth plant. (Source: https://www.amtaorg.com/wp-content/uploads/07_Membrane_Desalination_Power_Usage_Put_In_Perspective.pdf )

A solar farm such as this one planned for Cornwall
https://www.goodenergy.co.uk/media/1096/delabole-solar.pdf
takes up 25 acres and produces 3MW of electricity.

Reaching for my calculator shows that the power from that solar farm (when it's running at full output, i.e. when the sun's shining brightly) could desalinate 857 cubic metres of seawater per hour.

The average household consumption of water in the UK is around 0.35 cubic metres. (Source: https://energysavingtrust.org.uk/sites/default/files/reports/AtHomewithWater%287%29.pdf )

Reaching for my calculator again shows that for each hour the 25 acre solar farm is producing maximum energy it could desalinate enough water for the daily requirements of 2455 homes. However it won't produce energy during darkness and it will run at considerably less output during cloudy conditions. Further, my calculations don't take into account the energy requirements of all the factories and offices where the residents of those homes will be working.

So the economics don't seem to be too good. In practice the Perth desalination plant draws much of its energy from wind power, rather than from solar power.
In the case of the Middle East and a few other locations, the presence of abundant oil and gas resources in local ownership means that these are usually the primary energy source of choice, at least for now.
I don't know the answer but can state with some authority, the Perth, P&K has no need of this witchcraft. :-)
I agree with Douglas - I am sitting in the aforementioned city and we are currently having a rare break between showers/torrential rain
The excuse that we don't have them is always that they need too much power. So build a few more nuclear plants and stop prevaricating. Don't need to rely on solar yet.
Fiction-factory can of course endorse that comment about Perth. I like Perth though- it Feels Like Heaven to me
The boss and I are having a wee 2 night break there next week.
Didn't Saudi Arabia once plan to tow ice-bergs from Antarctica to acquire fresh water? That must have been an April Fools joke, mustn't it? Or was it?
Thanks Chris.
Engineers from the Department of Energy of Politecnico di Torino has developed a new model to desalinate seawater in a sustainable and low-cost way, utilizing solar energy extra efficiently. Compared to previous solutions, it can double the amount of water generated at given solar energy, and it may be subject to further efficiency improvement soon.

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