More Generating 240 volt AC

eh? That I really don't believe. It might store liquid Hydrogen but it will be at normal temperature but a rather high pressure. I suspect some semi educated mejia graduate journo has just looked up the temperature that hydrogen liquifies at under normal atmospheric pressure...

Or even the correct figures, which show that the maximum available boiling point for liquid hydrogen is -240 C at 13 bar. At atmospheric pressure, it's -253 C. Liquifying Hydrogen at normal ambient temperatures involves pressures "off the scale" according to NASA's handy webpage on the subject. :-)

The -250 C figure is straight off the BMW website, by the way. ;-)

I thought there was supposed to be a metal hydride tank system which avoided the need for high pressure storage ?

Steve

That off the scale pressure doesn't surpise me. I still doubt that the stuff is being stored at -250 ish deg C though. See Mr Taylor's comment about a metal hydride system.

OK so s/semi educated mejia graduate journo/semi educated marketing droid/

I did, & I checked. Current state of the art seems to be that MH storage is too low in hydrogen storage density, & too complex to run to put into a series production vehicle. The tank BMW quote is about 55Kg total weight to hold 8Kg of gas, (About 15% of the storage weight is fuel) MH storage density is currently peaking at about 10% of the metal hydride weight, then you have the parasitic weight of the heat exchangers, pressure vessel & general plumbing complications to recover the gas from the hydride. Cryogenic liquid storage at reasonably low pressure seems to be the most efficient storage method at the moment. Lets face it, if it could be done with less weight for the same fuel flow rate as cryogenic tanks, NASA would be using it instead of liquid hydrogen for rocket fuel. :-)

The figures quoted support other reading I've done over the last year or two in general science magazines here & in France.

In article , AJH writes

I agree. 50:50 seems to work for us, except in the winter (see previous post etc.)

Quite understood. It's this elegant solution that I like.

Indeed. Ideally, if I get the extra tank it will be the heat exchanger for the solar system. I'll move the gas to the lower coil on the main tank and either ignore the higher one or fit a valve to give the choice of either. There are unused spigots for a circulating DHW system I can use to connect in, such that it should convect nicely if the tanks are in reasonable proximity.

Indeed. I wanted a thermal store for that reason (and the ability to cope with peak demand better than a tank), but nobody locally was up for it. On balance it hasn't worked out too bad, and we do notice the reduced energy use from the solar 'boost'. Yes, our bills have risen, but probably not nearly as badly as they might have done.

Regards,

Simonm.