"Wrt hydrogen storage + shipment: both California and Iceland had proposals (and trials) where hydrogen formed a significant part of the energy distribution network (audience reminder: hydrogen is not an energy source in the same way as fossil fuels). BMW even made a "production" hydrogen car. Were all these ventures doomed to technological failure from the start, or were there other issues e.g. Iceland trial's reliance on well known green pioneer, er Shell?"
Firstly Iceland is a state of 300k people. California is a state whose GDP would put it at *least* in the turnover of the top 20 world economies. Both are energy rich either by oil and wind or geothermal and hydroelectricity.
That's important because the issues around H2 are only *partly* technological. They can be solved on a (relatively) small scale. The problem is how much *money* you're prepared to invest to do so on a *large* scale.
I note the Iceland scheme was kick started by a Chemistry professor. Chemists *love* the simplicity of H2 combustion (barely 19 species to model H2/O2 combustion IIRC).
The California plans talks about a minimum of 50 filling stations but not *how* they make their Hydrogen. One of the US hydrogen reports indicates there is 1 million miles of natural gas pipeline versus 1200 miles of Hydrogen. This is not surprising. Room temp H2 piping is welded stainless steel. IE It's *very* expensive relative to normal gas piping. If you want to send as a liquid you're looking at "Vacuum jacketed" IE *concentric* welded stainless steel lines with a vacuum between. Liquifying it take 1/3 of the energy carried per unit mas of H2 your liquifying.
That suggests they will make H2 by catalytic processing of natural gas, a *highly* energy intensive process to produce the "clean" fuel. They will then take a shed load *more* energy either to compress it to a reasonable volume or liquify it.
My point is that Hydrogen has a *lot* of problems which make the idea of it as a "drop in" replacement for *any* fuel ridiculous.
Key point. Hydrogen is an *exceptionally* awkward fuel to make, transport and store due to its natural *physical* properties, which don't change unless you live somewhere like Pluto. It has *very* poor energy *density*. Ikg of gasoline gives c62Mj at roughly 1.4l. 1Kg of H2 gives c112Mj at c12.9l (*If* it's at -253c), but as you've spent 1/3 of that to liquify it in the first place. 20% more energy at only 820% more volume.
Desertec is attractive because it works *with* existing distribution networks, not against them. It uses pedestrian (but *very* large scale) technology to deliver a cost *effective* solution to the problem on a large scale.
If you ignore economics almost *any* scheme is viable on a small scale. However if it's not economic to begin with there is *no* incentive to grow and it will remain a dependent on (massive) state intervention.
You have to be clear *what* problem you are trying to solve. Call me an arrogant b*£$"$d but I think they have it wrong. Liquids fuels are easy to handle, store and move and allow vehicles to be "recharged" quickly. It is *possible* to make a steam powered car (and in the UK the steam powered speed record was recently broken), but why would you *want* to?
IMHO the ideal system would be a flywheel storage drive EV (no loss of capacity aging modes). However for the near term a system which uses the sun to generate electricity to charge a hybrid flywheel/fuel cell vehicle fueled by a renewable liquid fuel or near cryogen (LNG, LPG, Methanol perhaps). The concern is not so much CO2 in Earth's atmosphere, it's the *rising* level of CO2. Re-cycling that CO2 would slow it's growth and be relatively easy to do using *existing* infrastructure.