Fresh Water from Solar

As solar gets cheaper and cheaper it might be time to think of what could be done with all that excess capacity, or just explore non-traditional uses for this sort of electricity generation. Many places around the world already use desalination to make fresh water from abundant salt water. The problem is the expense (as well as the pollution) from the energy used.

I was wondering what it would take to make your own fresh water using solar. Lets use a rough figure of 15,000 kWh for 1 million gallons of water. This comes to 15 wH per gallon. That is, a 15 Watt energy source can make a gallon of water per hour. This is rough and maybe not to scale, since the numbers are probably for larger and perhaps more efficient large installations. But perhaps not.

A normal 400W solar panel running for 8 hours would give over 200 gallons of water. Assuming an American uses 50 gallons of fresh water per day (probably a large number due to various forms of waste and inefficiency) this means one solar panel can supply an American family of four with it’s fresh water needs. I’m a bit surprised by this. Given some of my water bills I wonder if it may even be cost effective in many places where municipal water is available. Somebody check my math.

Update: several home reverse osmosis units are available for about $300. They don’t seem to be using any sort of excessive power and claim to produce on the order of 500 gallons per day. Could be much less than one solar panel to produce clean water for a family of four, and you could do it easily today.

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