>> I've long thought that a home "gasometer" system should be viable -
>> miniature version of those used here for coal gas in days of yore. 
>> .
>> Electrolyse water to Hydrogen and store enough for a few days 
>> heating
>> demand. Oxygen a bonus.

> Not really a "bonus", isn't it? Pretty much the same amount it 
> generates it
> also consumes when burning the hydrogen.

No.
It can happily burn atmospheric Oxygen with no cost or great problems 
and you can save the pure gaseous Oxygen for some other purpose if you 
value it. The main difference is that using pure O2 you have no 
emissions problems whereas with atmospheric Oxygen you get some 
Nitrogen products - but not vast amount at near atmospheric operation.

Ideal for driving a Whispergen :-)

The following calculations (E&OE) suggest that a 2m tall x 2m diameter 
tank (6 m^3) will store about 20 kWh of Hydrogen at essentially zero 
pressure.
That's $NZ2-$NZ3 worth at present.  If you halved power costs due to 
night store supply and cycled this daily thats an annual 'saving' of 
around $NZ500 per year. You'd have to have economies of scale to make 
that worthwhile - would probably support a $2500 - $4000 range price 
tag all up. Done on  a very large scale this would help delay power 
line upgrades and would thus have further economic benefits.

Quick calculation for use as a home peak-shifter.
Hydrogen combustion energy is about 39 kWh/kg.
1 kg = 500 mol =~ 11 m^3 at STP.
Hmm - a bit voluminous.
About 0.3 m^3/kWh at STP.
Compress that to 1 atmosphere above ambient and halve it.
To get say 20 kWh which is a useful heating load for 1 day for most 
houses requires 6 m^3 at atmospheric, 3 m^3 at 1 atmosphere.

Even a 6 m^3 tank is "only" a 1.8 m per side cube or a 2m high by 2m 
diameter tank - not overly large compared to many water tanks here.

You could store hydrogen over water with  floating tank with no bottom 
or pump water in and out (lots of water) - maybe to a second tank or 
use a bladder or bag. The latter is doable but liable to have a 
shorter lifetime and Hydrogen diffusion is liable to be an issue.

Storage in metal hydrides would get volume down but add to cost and 
other issues.


        Russell.. .

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