One small hole: the oxygen is released in form of...[drum roll, please] ... carbon monoxide [unpleasant poison, but could be used as a gas fuel or for synthesis] - their charcoal is going to end as carbon monoxide (which nobody is going to release on large scale) or dioxide, which is... [drum roll, please] ...a "greenhouse gas". The whole thing is an 120+ years old manufacturing process for zinc, but uses sunlight as a heat source instead of burning even more coal for the purpose.
Since zinc is [in theory] recyclable like a catalyst, they are virtually burning carbon (charcoal) in water vapor, generating hydrogen and CO or CO2.
So how is the Zinc turned into hydrogen to be burnt in your car??? How much hydrogen to you get per pound of Zinc? What are the other byproducts?
It sounds like both charcoal and sunlight are consumed to produce the end product.
I'm not even slightly chemically literate... But it sure sounds like there's some major holes in this story...