I took a look at the website for the guys with the do-it-yourself plug-in hybrids. I think the guys are sensible people with coherent arguments, and they have been misrepresented by the press that loves headlines. It is the press that claims 80 MPG or whatever. The guys (California Cars or whatever they were called) acknowlege that they are running much of the time as en electric vehicle; indeed that is their aim, and pictures of the EV button on the 'European Version' of the Prius highlights the fact they are thinking ELECTRIC VEHICLE, with a small engine to run as a normal hybrid over longer distances than battery only operation would allow.
For a very few people, that would make envirnmental sense. Those people are the ones with access to green electricity, eg a guy with an old watermill by the river past his house running a generator and recharging the vehicle when not in use. Clearly most people don't have green electricity. It might also make economic sense to people with dirt cheap electricity and expensive liquid fuels.
The thrust of their argument is environmental - liberation from oil, and they note the use of OFFPEAK electricity. The batteries effectively provide a storage of the electricity for late use.
Looking at things from a global planning point of view, balancing loads on electricity networks is maybe better done by using a timer to start dishwashers and washing machines, heating water in a well agged boiler overnight and using it during the day etc. If there is a need to store offpeak electricity in batteries for later use, it is far more sensible to have the batteries fixed in the house and burn liquid fuel for a vehicle, than to carry the batteries around. So while they have the best of intentions, what they are proposing is not the most efficient way forward.
Basically, electric only vehicle operation only makes environmental sense where green electricity is available, and economic sense where the electricity is low cost. It is good that people are doing the research and proving the concepts and for some eco-warriors the idea would actually work, but for Joe Public, clean electicity needs to come first and so the plug-in hybrid guys are sort of way ahead of their time.
When their time does come, and there is an excess of commonly available green electricity, in excess of what is required for more deserving cases - like households - they will still be up against green fuels like vegoil, bio-ethanol etc.
If a carmaker sold plug in hybrids with a wind turbine for your roof, big enough to power the house and have enough left over for the car, fine, otherwise forget it. Clearly this is technology worth looking at, but its going to remain odd-ball and not mainstream for a long long time.
Honda make gas (as in gaseous) powered cars and due to refuelling problems, also sell a compressor so that people can refuel their cars from the mains gas in their houses.
So my remarks about the car maker selling the turbine to recharge it are only 99% jest. There is a 1% of prediction in what I'm saying.
I think ultimately many people will buy vehicles and buy a refuelling mechanism to match it. Kits are available on the internet to make vegetable oil from vegetables, with combustion in mind. We can see the trend in operation on these fora [forums] with people doing biogas conversions due to having a source of biogas, or people in the country doing vegoil conversions.
As oil supplies drop below demand, alternative sources are required. The oil companies cannot pretend hydrogen is a one size fits all pullover, and diversity is the key. This forum is scattered with fringe ideas that will take niche shares of a future car market.
Plug-in hybrids is going to be one of those niches. Prius and Ford Escape plug-in recharge conversion kits will appear on the aftermarket and some time or other an OEM might advertise their green credentials by selling a plug-in hybrid car. But clean electricity for cars while household electricity is still dirty, ain't going to happen big-time and any push in that direction is misguided.