I think using H2 to power cars is a dumb idea, particularly for the reason you mentioned. Nature has invented many energy-dense liquids and solids that would work much better (some of which we use in slightly modified form). I'm not sure density matters so much if you're sending the H2 through a pipe, and of course the low density is an advantage if you're using it for buoyancy. But the main idea is to transport the water without all the extra weight of the oxygen, not that weight is always an issue. On 23-Apr-15 20:13, meekerdb wrote:
One problem with H2 as a fuel is its very low density. H2 powered cars suffer a significant inefficiency just in having to compress the H2 in order to get a reasonable sized tank.
Brent
On 4/23/2015 3:42 AM, Mike Speciner wrote:
What if you used solar to just split off the hydrogen? Then transport just the hydrogen and use it to reconstitute water wherever needed, simultaneously retrieving at least some of the energy? How efficient could that be made? I know there's work being done to produce hydrogen directly from sunlight and water (though I don't know if it works for salt water), and of course there's work being done on hydrogen fuel cells. If you aren't worried about Hindenburgs, you could also piggyback other transportation on the hydrogen.
On 23-Apr-15 00:23, meekerdb wrote:
On 4/22/2015 8:07 PM, Henry Baker wrote:
Thanks, Gene for the terrific analysis.
Let's say that RO requires 5 kWh/m^3.
'A typical "150 watt" solar module is about a square meter in size. Such a module may be expected to produce 0.75 kWh every day, on average, after taking into account the weather and the latitude, for an insolation of 5 sun hours/day.'
It's not clear why you should convert to electrical power in order to desalinate water. You need some for pumping the water around, but you can use solar energy directly to heat and distill water in imitation of the atmospheric rain cycle. It'll take some research to figure out how efficient this would be, but I think it's a lot more efficient than going through the solar photons to electricity step.
Brent
http://en.wikipedia.org/wiki/Photovoltaic_system
1 cubic meter = 264.172052 US gallons
Each person requires ~ 50 gallons = ~1/5 m^3 of water per day, or about 1kWh per day for energy for desalinization.
So each person requires about 2 m^2 = ~21 sqft (~ size of a large 3'x7' bed) of solar cells just to power his/her desalinization needs.
Clearly, there is more than enough roof area on most (California) homes to provide enough power to desalinize the water for its occupants. So even if we're off by a factor of 2-4x, this is still reasonable.
So perhaps the answer is piping seawater to people's homes and doing distributed desalinization?
At 06:40 PM 4/22/2015, Eugene Salamin via math-fun wrote:
According to [ http://en.wikipedia.org/wiki/Desalination ], reverse osmosis requires 3-5.5 kWh/m^3, just for the reverse osmoses, and excluding the energy needed to operate the facility.
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