For Drinking Water in Drought, California Looks Warily to Sea

http://www.nytimes.com/2015/04/12/science/drinking-seawater-looks-ever-more-palatable-to-californians.html

by jsc123 • 11 years ago

3 5 11 years ago

Use solar power for desalination. It is very easy and, with some engineering work, I expect it could be made economical.

I learned to do this in the boy scouts: dug a hole, piss in the hole, put a cup in the bottom of the hole, cover the hole with a sheet of clear plastic then weight down the center of the plastic with a small stone.

The air inside the hole/plastic container will be quite a lot warmer than the outside air. Eventually water droplets will condense on the underside of the plastic then run down the slope and drip into the cup.

I can think of all kinds of ways to scale this up to industrial capacity.

Much of California is either desert or quite arid, but much of the arid area is right next to the ocean.

prostoalex• 11 years ago

Yeah, much of the "high cost of desalination" problem is "high energy cost" problem.

Much of the industrial solar capacity will come from gigawatt plants that utilities themselves are building - while small distributed systems are nice, eventually economies of scale play out better https://gigaom.com/2015/01/20/a-special-report-the-rise-of-a...

dalke2• 11 years ago

Direct solar desalination as you suggest has a limit of about 4 sq. meters/liter/day. (Says http://en.wikipedia.org/wiki/Solar_desalination ). The L.A. Department of Water and Power delivers some "545,910 acre feet of water to 694,705 accounts" (http://sustainablecities.usc.edu/research/Chapter%203.%20LAD... ). That's 673 million cubic meters.

To replace that water with desal would require 7E9 sq meters or 7 379 sq. km or 2849 sq. miles, or about 4x the size of the L.A. metro area. Assuming I didn't drop a few powers of 10.

There isn't the space for that in L.A. There's also pumping costs to get sea water up and through the desal system.

Reverse osmosis seems to be the way that everyone is going. Including indirect RO through solar power. Power is a lot easier to move around than water.

MichaelCrawford2• 11 years ago

Thanks for the calculations.

I expect there are ways I can improve upon that though. Note that there are lots of inefficiencies in the method I described, such as the resulting fresh water being hot.

Perhaps with the use of a heat exchanger to recover the waste heat...

For Drinking Water in Drought, California Looks Warily to Sea

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