Now this is seriously fascinating

Using seawater to grow crops.

It\’s always possible that there\’s some economic hitch in here: one that I\’m not competent to divine. But they do seem to be saying that there isn\’t one, that this is actually profitable, without subsidy.

So, parabolic reflectors concentrating on a heat exchanger which heats up seawater which is fed into a greenhouse where plants are grown hydroponically. There\’s a bit more about cooling it as well.

If this does work then absolutely great. No soil issues, no fresh water issues. Very small (backup only) fossil fuel costs.

I have a feeling that this will only work as what I would call \”truck farming\” though. It\’s not going to work for mass carbohydrate crops like rice, wheat or potatoes or maize. Which do, after all, still provide the majority of calories around the world. But for high value (relatively of course, this is farming and food we\’re talking about) items like tomatoes, strawberries, cucumbers, peppers etc they do indeed claim that it works.

And if it really does work then there are island communities (Cabo Verde is mentioned in the piece, but there would be many more like the Caribbean ones) that should just be gagging for this.

I don\’t know if it really does \”work\” in a proper economic sense. Perhaps one of our resident farming experts could tell us? But if it does it sounds like a damn good idea to me. There\’s plenty of places around the world with shitty soil, vast amounts of sunshine and seawater close to hand.

24 thoughts on “Now this is seriously fascinating”

  1. Solar desalination is nothing new in desert areas. Most such systems use PV together with reverse osmosis or a membrane-based technology; so I’m curious as to why this man is boiling the water instead.

    Once you’ve created the clean water, what you do with it is a completely separate matter. It might be more economic to provide clean drinking water for sheep; or maybe to build hotels with vast swimming pools in the desert and attract tourists (it worked for Dubai and Las Vegas). Food production doesn’t necessarily provide the most revenue from that clean water.

  2. The current set up processing 10,000 litres of water a day would be churning out 3.5 tons of salt a day. The proposed new greenhouse, 40 times bigger, would presumably churn out 140 tons of salt every day, or 50,000 tons a year. Dealing with that is going to be non-trivial.

  3. It’s a bit hard to understand why they’re using 10,000 litres/day to irrigate 1/2 an acre, under glass. 5 litres/m2 would be more than adequate, planting in the ground in the open air. Certainly is for me at similar temperatures. Under glass, using hydroponics, the water use should be a fraction of that.
    The only thing I can think of is they’re using a lot with their evaporative cooling but, given they’ve access to presumably cool seawater, they shouldn’t have too much trouble precipitating much of that out again. It’s not too dissimilar a problem to distilling the fresh in the first place.

  4. Chris, I think that is wrong by a factor of 100. Sea water contains approx 3.5 gm/litre salt. 10,000 litres therefore contain about 35kg – and so on.

  5. There doesn’t appear to be any explanation as to what happens to the vast quantities of salt that are produced.

    It can be smuggled into quiet coves around Britain on row-boats after the health fascists have banned salt in food.

    More seriously, can it not just be dumped at sea?

  6. I think it should be moulded into kiln dried bricks, coated in plastic and used to build a dazzling palace of salt

    Obviously

  7. To Andrew M’s query (#1) about why they don’t use osmosis or a membrane system, would that perhaps also filter out the nutrients?

    If it’s hydroponics then there’s no soil, I think? So assuming the plants are getting all the nutrients from the seawater rather than bags of fertiliser, then they need to get the salt out of the seawater whilst leaving the nutrients in.

    I’m utterly ignorant about all of this, but my guess is that that is the new clever bit.

    It might also explain why they need so much water (bis, #4), if it’s providing the nutrients at a very low level of concentration.

  8. Tim, ever noticed the health facists that often have a go about what other people eat or drink are often the same people who on the subject of abortion claim ‘its my body my decision’? Without of course extending that to its conclusion.

  9. “There doesn’t appear to be any explanation as to what happens to the vast quantities of salt that are produced.”
    Jeez!
    Hasn’t it occurred, there’s a very convenient place to dump it where it will do no harm whatsoever? Where it came from in the first place.

  10. “Most such systems use PV” they seem to be using solar induction (similar to a solar power tower) with gas for a backup. PV probably would be much more inefficient. The gripes from the inventor seems to be that they’ve actually made something useful so that’s un green as we all know you can’t make economic things and still be environmentally friendly! 🙂

  11. blink in spain-“Hasn’t it occurred, there’s a very convenient place to dump it where it will do no harm whatsoever? Where it came from in the first place.”
    You are correct, I apologise for my mistake, my sums were a little wrong.
    I imagined that dumping 50,000 tons of salt in the sea right next to when the water was piped in from might drastically increase the salinity of the incoming water.

  12. Maybe it’s a confusion in the article, but I can’t see where the “inventive step” is here.

    Solar powered evaporation / condensation is nothing new. We used to call it rain.

    Desert soils are not necessarily infertile, so why choose somewhere that needs hydroponics?

    My suspicion is that the diesel engine is designed to pump CO2 into the greenhouse (which is there to ensure concentration of the gas), CO2 being a well known source of plant food.

  13. If anyone’s interested there’s an article about this on Wiki:
    http://en.wikipedia.org/wiki/Seawater_greenhouse

    Looks like that 10,000 litres/day may either be: 1) The seawater uptake In which case much of it may be returned to the sea at a higher salt concentration.
    2)The amount of freshwater the system can produce as a by product
    3)Or, one supposes, made up because an impressively large number always helps.

    As usual with Graun technology articles, this one is a bit light on…well…the technology. But lotsa luverly woo, of course.

  14. On the feasibility or not.

    Its a high capital cost, which is not going to be offset by cheap land. However, if you can get high yields, if you are replacing produce flown in from far away and if you can get a premium price, then it might just work.

  15. Chris G: “I imagined that dumping 50,000 tons of salt in the sea right next to when the water was piped in from might drastically increase the salinity of the incoming water.”

    I think not. The ocean is big. Dumping 350 kg per day won’t make a lot of difference. Particularly if you can do it as a water solution and pump it further away in a pipe .

  16. bloke in france
    “Maybe it’s a confusion in the article, but I can’t see where the “inventive step” is here.”

    It is quite clever. If you want to raise crops in very arid conditions, you need to use a lot of irrigation because you lose an enormous amount through evaporation. Putting the crop under glass conserves the water but now you’ve literally a greenhouse effect. The temperature under glass goes too high to grow anything. Evaporative cooling reduces the the air temperature & the clever part was realising it didn’t matter if you use seawater to do it. As you’ve a flow of salt free moisture running through, why let it go to waste if it can be captured at the other end by condensation? You now find you’ve, effectively, built a big distillation plant with crops growing in it.
    What’s a little puzzling, though, is why they’re expecting to be collecting salt. If it’s crystallising out in the evaporator stage, it’d be quite a problem clearing it. I’d have thought running the flow at a rate where the brine concentrates but doesn’t precipitate would let you just pump the stuff back into the sea. Much easier operation & it’s not as if the salt was really worth anything. Salt pans, where you run the seawater in & just let it evaporate, are simplicity itself. The value is created bulldozing it into heaps & trucking it out.

  17. has anyone seen the dazzling piles of salt at Aigues-Mortes…originally built by Louis XI – Saint-Louis- for his crusade, and now high above the “catastrophically rising sea-level”. And in one ot the towers of the fortress, there is a story about a body of a captive that was preserved in salt for ransom. It makes you think.

  18. So Much For Subtlety

    Serf – “However, if you can get high yields, if you are replacing produce flown in from far away and if you can get a premium price, then it might just work.”

    If. This is in South Australia? If I remember the area right, it is just to the north of the place Jacob’s Creek wine comes from. So agriculture is not unknown in the region. Dubai might be a better bet.

    19pjt – “I think not. The ocean is big. Dumping 350 kg per day won’t make a lot of difference. Particularly if you can do it as a water solution and pump it further away in a pipe .”

    Environmentalists and regulations are tough on desalination plants. They too dump their salt back in the sea, but they are constantly watched to make sure even local concentrations of salt do not rise too high. It shouldn’t be a problem but that doesn’t stop anyone trying to make it one.

  19. So Much For Subtlety

    Richard – “To Andrew M’s query (#1) about why they don’t use osmosis or a membrane system, would that perhaps also filter out the nutrients?”

    They are boiling the water. This is what is usually known as stupid. So the nutrients would stay with the salt anyway. It is stupid because of what they want to do is modest so it is needlessly expensive.

    If you want to do this sort of thing, why bother boiling the water? With solar collectors that use oil to transfer the heat. Insanely expensive. Build a Greenhouse. Run channels of salt water down the middle. When the sun shines, the water will evaporate. Bring in the fresh salt water along pipes that you lay where you want plants to grow. That pre-warms the salt water. The fresh water will condense along the outside of the pipes. It will also trickle down the sides of the greenhouse, especially at night.

    Problem solved. Cheaply. Or at least cheaper.

    I sense some fools and their money about to be parted.

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