Yet-another technology that will save us.
Call me back when I can a) buy a car with it, b) that car doesn't cost more than a conventional car (including long-term maintenance and, say, 10 years replacements of COMPULSORY items - e.g. batteries, fuel cells, etc.), c) that car gets me approximately the same MPG as currently, or better, d) that car has a range that means I can hit Scotland on one tank like my current 15-year-old car, and d) I can actually buy the damn fuel for it in the majority of petrol stations.
Because I've heard a story like this every month for the last 20 years and still haven't seen a car that can do that (or even come close) without using petrol. Hell, the *only* electricity supply point I've seen in my town for electric cars is actually in a council car park to fuel their little run-around cars (so it's not for public use). It's barely used (I assume they have a depot somewhere and that one's "just for show") and when it is, the little van is basically parked there overnight in order to charge.
I don't even need it to be a huge car, a little Smart-like thing would do. Hell, if it was single-person it would still work for commuting. But the practical problems of getting the car in the first place, and then driving it around in any reasonable amount or any reasonable distance mean that all the fancy new-age cars in the world can't cope with the average commute (who cares about replacing some old granny's car with an energy-efficient one if she tops up £10 in fuel once a month? She will NEVER make the cost of the vehicle and that vehicle's environmental impact back in her new car. The people you need to move over are the £400/month crowd and the commercial users).
1) Car cost (for fuel components and engine for that fuel, because the rest is pretty standardised)
2) Fuel cost
3) Fuel capacity
4) Fuel longevity
5) Fuel availability
6) Fuelling time
Spot the problem? Yes, it's the fuel. Nothing else, just the fuel you're using. You can run a can on whisky if you want, for proof of concept, but the fact of the matter is that it will mess your car up and/or not compete with petroleum-based fuels. Until it does (or the petrol runs out), you don't really have much of a product.
You know who've been seeing the most success in energy efficiency taken over the decades? Dairies with their milk floats. Hell, when I was a nipper, they were all-electric and it's a small step from them to make that electricity come from a renewable or cost-efficient source if you really want it to.
Sure, I've seen a lot of "hybrid" cars around. I've also seen their repair price tags but one thing I haven't seen is their second-hand value (which I'm assuming to be almost non-existent), which is where a lot of cars end up. Not many people own, or have ever owned, a vehicle from new. Not many people will pay for a "new" car that basically needs the value of the car paid again for replacement parts and zero secondhand value.
But an LPG conversion for my 15-year-old car costs £800 and will only take up my spare-wheel space. It might damage my valves over time but, come on, it's a 15-year-old car already so new "more resistant" valves are included in the conversion price and will probably last longer than the car anyway. And I can "save" the cost of the installation within a year of driving. That's what you're competing with, not top-end brand-new vehicles.
By comparison, even the cheapest all-electric car, fuel-cell car or any other alternative vehicle costs more than I've ever paid for every car I've owned, every repair I've ever had + several year's-worth of fuel before I can even get it moving.
It's all pipe-dream and fantasy until you make a viable vehicle that can do all that, and I can stroll into any petrol station and find a pump for it. Hell, I found a 4-star pump the other day so technically I've seen as many of those lately as I have electric filling points (and I've seen zero hydrogen points whatsoever).
Progress is good, but this is like telling me that in fifty years time we'll be eating pills and flying our own cars around. It's a great fantasy, and makes a good science project, but until it's viable the petrol is going to be favoured. You need to make it viable before we are priced out of petrol, too, because if the only alternative is expensive petrol, most large fuel users will HAVE to still use the petrol anyway.