eli5: Why is it so difficult to desalinate sea water to solve water issues?
In: 1972
Energy energy energy. The absolute theoretical minimum energy needed to separate water from seawater is about 1.1 kilowatt hours per cubic meter. The practical theoretical limit for a perfect machine of reasonable size is about 2 kWh per cubic meter. At average American electricity rates that’s about $0.20 a cubic meter. Not bad, cheaper than Dasani!
The cost of actual plants being built today is not too far from this, about $0.40 or $0.50 per kWh.
But it takes about 1 cubic meter of water to grow 1 kilogram of corn, and 1 kilogram of corn sells for about $0.20 at the time I write this.
So you can see that for drinking water desalination is a practical option, but for agriculture it can’t compete with places that have natural rainfall and irrigation.
https://www.sciencedirect.com/science/article/pii/S1470160X14002660
https://pubs.acs.org/doi/10.1021/acs.jchemed.0c01194#
https://markets.businessinsider.com/commodities/corn-price
https://smartwatermagazine.com/blogs/carlos-cosin/evolution-rates-desalination-part-i?amp
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