hydrogen from solar
 

would it not be possible to extract hydrogen from water using solar panels at home and then compress it with a hydrogen compressor [the expensive bit] for use either as a fuel supplement or as a complete replacement to petrol.
dunno just a thought...

Yes, you can do that. But, its horribly inefficient even though its renewable.

Solar PV is at most ~15% efficient, then you take the electrolysis efficiency hit, and I don't even know what that is, then you take the ICE engine hit on top of that which is probably around 20% efficient in normal use, and then add the compressing power on top of that. You're talking about a MASSIVE solar array to power a car. At least 5X the solar power vs an EV. You're much better off using that solar energy to charge an EV.

Edit, forgot another loss.

There is no reason to make hydrogen from solar or own a hydrogen compressor unless for some reason you have a constant lavish over capacity of PV all the time.

The efficiency of a cold electrolysis rig is around 20%.

I calculated it will take more like 10 to 20 times the power to run a hydrogen from electrolysis car as opposed to an EV.

Hydrogen sounds nice, but is not exactly so cost-effective in short to medium term.
http://fotolog.com/cripple_rooster - blog oficial: Hidrogênio: futuro do pretérito?