dear Mervyn, solar distillation will not leave behind any salty reject water. imagine a salt flats and you cover it with clear plastic sheeting. you have salt left over. and you have distilled water.
Published by Eros Kaw, Biocleaner Inc. - Chief Tech Support
1 Comment
No one should discourage new concepts, but a shot of reality is needed to put them in context.
Referring to your statement that there is no salty brine left over....that is inaccurate. You still have a considerable amount of salt mixed with contaminants from the ocean water left behind. And it will take quite a while longer to reduce that brine to dry minerals, far longer than is practical if one wants maximum water production, and then you need to dispose of it. Where does all the salt get disposed of?
If it is above ground you will need impermeable basins where millions of tonnes can be stored because rainfall will dissolve the surface salt and produce brine which will leach into soils and water ways, and aquifers and kill everything it touches. Then once that basin is full....what do you do with it, and where do you find the next one? And there needs to be a method of covering those mountains of salt as the wind will blow it onto adjacent land, rendering them infertile.
What you are creating are massive storage sites on land for salt contamination...a ticking time bomb for future generations to deal with.
Another choice will be to ship it back out to sea and dump it, at considerable expense. It will have to be loaded onto trucks and shipped to ocean terminals and loaded onto special ships that are equipped to dump at sea .... and any coastal country employing this method will need a lot of them because the trucking, loading, shipping and dumping will take considerable time....that is not therefore a cheap proposition! And it must be in deep water because the sudden shock on marine ecosystems of high salt concentrations will kill marine life, even in open water.
The concept of solar distillation is not new, but the logistics in dealing with the waste material need to be overcome FIRST! Nothing is a simple as first envisioned!
Saying that we can duplicate the natural evaporation process and solve all our water problems isn’t recognizing the scale of the problem, especially for agriculture. Let’s look at Saudi Arabia for instance.
They are the largest mechanical producers of desalinated water on the planet, producing 5,760,000 m3 a day. At your requirement of electricity that comes to 14, 400,000 KW hours a day, every day…without end. Now most of that can be derived from solar but any operations at night time requires another source of electricity, if of course it produces anything at night. And on days of heavy cloud, and cooler temperatures, there won't be much in the way of fresh water production.
But, there is no indication of the scale of the unit, and the output of distilled water, ie: m3 per hour, and natural desalination at room temperature is very very slow! Since these units cannot operate well at night due to the drop in air temperature (even in the desert) and with no sun, they can only produce for part of the day…..and at what volume? I suspect a minimal supply!
Now consider this … Saudi Arabia is only 30 million people, and that 5,760,000m3 a day only supplies 70% of their drinking water, and only 6% of the total water use in the country. Which means they use 94% of their water for industry and agriculture, and that’s a small amount because they import 90% of their food (and have very little manufacturing) and don’t use a single drop of desalinated water to produce the remaining 10%, which comes from aquifers.
It’s fine to say….”here is a simple system, why don’t you people recognize what God has given us!” It’s quite another to duplicate the natural system at enough scale to create an adequate supply, especially for agriculture which is 15 times greater than drinking water requirements, and in greater shortage for future populations due to drought and climate change in dry regions.
Solar desalination and in particular your system is viable for small scale production, but has many hurdles to overcome in disposal of the toxic bi-product, and those ensuing costs. As well as the fact that it will only provide a portion of the drinking water requirement and won’t be of scale to provide what agriculture requires.
It’s one solution on a small scale, and relatively cheap, but it isn’t gonna save the planet from a fresh water shortage.
A 25mm rainfall over 24 hours (a drizzle) covering 100sqkm (just 10km/10km produces 2.5 million m3 of fresh water. On an area of that small size, basically a postage stamp for any agricultural region, you’d have to produce that 2.5 million m3 every week at least, in a hot desert climate. In Saudi Arabia, they require 1000mm in less than 90 days to produce a crop of wheat. (That's 11mm per day or 11 times what this estimated calculation amounts to) How many of your units would it require to do that??? Probably several hundred or more!
Let’s speculate at the numbers. 2.5 million m3 divided by 7 days = 357,142m3 per day. Desalination at room temp is very slow, and you’d be lucky to get 10 m3 per day out of a unit. And even if it was a massive operation at large scale, (way too expensive for developing countries to build a lot of) you might get 1000m3 per day (but I doubt it) . That means you would need 357 massive units operating nonstop just to accumulate 25mm over one week, nonstop. Units that size would require a footprint of at least 15 acres, including piping, water intake and bi-product discharge facilities…That means you have to cover 5,355 acres with desalination plants, just to produce 25mm of fresh water to 23,000 acres of agricultural land weekly. And in a desert climate, you'd need 10 times that much to irrigate a crop.
It will be a good addition for small scale drinking water, but isn’t reasonable to speculate that it will produce all the fresh water required for agriculture.
Published by Mervyn Byron