Science Buddies: "Ask an Expert"

Hello guys, how are you? It's my first post here.
I already found a topic in this forum about the same subject, but it seems dead, as the author do not post anything since Sep/2014...

I live in Brazil - SP, and currently there is a lot of talk about a lack of water in the next few months... So I decided to work in a possible way to get water from alternative sources.

In my researchs I found an article in wikipedia talking about an Atmospheric Water Generator (link: http://en.wikipedia.org/wiki/Atmospheri ... _generator) and decided to give it a try.

I'm thinking about making a "green" one, that means, one that use only renovable sources of energy (energy from wind in this case).

I made a drawing of my project. (Yes, I know that I suck at using "Paint"... )

Please tell me what you think (see image bellow)

Image:

Direct link if not displayed properly: http://i60.tinypic.com/35am615.jpg

I also have some doubts about this project... Could you please help me?

-First of all and most importantly: Is this project possible to be done?

-Which kind of motor should I use to generate like "12v" of energy to make the Peltier device work? (in the store I saw one that says 12v - 70w)

-Do I need to use something "between" the motor and the peltier device to avoid it to being damaged for example if the winds are too strong and I get more than the expected voltage?


Thank you all, and please sorry if I wrote something wrong. English is not my language and I wrote it with the help of google translator.

That's a fascinating problem, and you're going to find it's not as easy as you want it to be.

1) A computer fan can't be used as a generator. You can modify one (http://gadgetmakersblog.com/computer-fan-generator/) , or make your own with a cheap DC motor and a fan blade or propeller of some kind. You won't get more than a few watts at best though.

2) It takes a lot of energy to condense water out of the air. Commercial devices exist (here's a review from a few years ago: http://www.treehugger.com/clean-water/t ... -from.html) that do this exact function, but plugged into the wall. They draw 450 to 500 watts and can collect perhaps 3 gallons of water (24 pints) per day. If you only had 1/10 of the power, 50 watts, maybe you could collect 1/10 of the water (this is just a guess) or 2.4 pints per day.

Generating 50 watts continuously would be part of the challenge then. You can't generate continuous solar energy. If you had a nice sunny day you can count on 8 hours. average 50 watts, you would try for 150 watts during the sunny part of the day. That might require 15 square feet of solar panel. Using wind is something I'm not all that familar with, but a commercial windmill intended for sailboats and campers that puts out 100 watts in a moderate wind looks like this: http://www.energymatters.com.au/aerogen ... p-511.html and is about 1 meter or so in diameter.

If I were tackling this, I'd first set up your collector and power it from a wall supply. Make careful measurements of the ambient air temperature, the lowered temperature you achieve with your cooler, how much condensate you get and the amount of current consumed by the cooler (calculate power as watts if you like). Once you know what kind of output you might get and how much power that requires, you can tackle the problem of generating that power. A commercial windmill is pretty pricey. There are a lot of ways you might build one of your own - modify a computer fan if that sounds like fun, stick a propeller or a windmill blade on a little DC toy motor, or perhaps try a more elaborate windmill design. Solar is a lot easier to get but you will need a good bit of solar panel surface area. Figure about 10 watts per square foot.

I think a demonstration device is manageable if you have a reasonably unlimited amount of power. You'll find out that cheap, small power generators don't make much and that Peltier junction coolers aren't terribly efficient. If you consider using wall power as a plan B, go ahead and start experimenting. Running this on green/free energy is a tall order.

Howard