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View Diary: Alternative Energy Round-Up #4 (20 comments)

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  •  and as for drinking the water (2+ / 0-)
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    RosyFinch, CoEcoCe

    yes, it comes off as steam and can be condensed to give distilled water. But you don't want to waste it on humans, this is pure water - it should be routed back to the electrolysis unit which needs high purity water.

    •  ah! good point, so can water be also (0+ / 0-)

      produced on site, to supplement the self-generated water for the fuel-cell.?

      because if all the needed elements can be made locally then imagine dumping thousands, of even more of these water/electricity boxes all over the world to produce clean water and power in a democratized de-centralized way...
      fantastic.

      •  only 'makes' water if you burn gas (1+ / 0-)
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        CoEcoCe

        if you use solar to make H2 via electrolysis then you need to return the water produced by the fuel cell back to the electrolysis unit - which require high purity water, much higher purity than you do.  Waters stores 'de-energized' hydrogen, hydrogen gas stores energy; it's a closed loop that will need occasional additions of small amounts of water to make up for the hydrogen that leaks out.

        And even if it burns natural gas, the amount of water produced isn't much.  If you use 1 liter of methane:

        CH4 + 2 O2 => CO2 + 2 H2O

        you get 36 grams of water, close enough to 36 ml or about 1/28 of a liter of liquid water. A human needs 2 to 4 liters of water a day, and that's skipping bathing and so on.  So you'd need to burn 60 to 120 liters of natural gas a day to get that.  There's 28.3 liters per cubic foot, so you need to burn 2 to 4 cubic feet a day to get enough water to live off of.  Now in the U.S. a typical gas fueled (heat, hot water, cooking) home will consume 150 to 250 cubic feet of natural gas per day, producing roughly the same number of liters of water.  For 3 people per system that's a tad less than a poor peasant in dryland rural China gets and about half of what a person in the U.S. uses.

        That water comes at a cost of 48 grams of CO2 for every 36 grams of water, or around 1.34 kg CO2 per liter of water - and also produces about 4 kWh of electricity (4 kWH in 24 hours, or and average of 166 watts continuous output)  That amount of power is likely in excess of the needs of a poor family in the 3rd world (not all of which is developing), they're not likely to pay for what they can't use so they'd consume less gas and generate less water.

        For known technologies bigger is generally more efficient. Big wind turbines generate power, little rooftop wind turbines make take more energy to make, install, maintain, and dispose of then they will generate over their life.  

        A composting toilet takes you 'off the grid' in regards to sewers. But for high rise apartments and the shanty towns of developing nations there isn't anywhere near enough open ground to dump the output of the composting toilets onto; it would have to be hauled away by trucks at a higher cost - dollars and energy - than a sewage system would. And composting toilets waste the energy in the sewage; the garbage and sewage generated in the U.S. could generate an amount of methane equal to around 1/5 to 1/3 the total natural gas consumption of the country. But that only works in large systems that take advantage of the volume/area relationship (cube vs square) of big vs little containers; small systems make some gas, but not nearly as much and leave the effluent with a much higher BOD/COD than the big systems. The big systems have the potential to capture almost all the nutrients in the sewage and garbage for return to farmlands, the little ones leave those in the liquid effluent.

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