Make it a Volt/Ampera-style thing. Chuck out half the batteries, replace them with half a DCi (so about 750cc and 40ish HP peak, or 20 at its most efficient settings (~2000rpm and 80% throttle)) as a generator... direct connection to the wheels optional, but apparently they managed it in the Ampera by dint of a crazy planetary drive a la the Prius (but not as ****).
A constant 20hp is enough for a 60mph cruise, and 40hp for mid-80s mph on the flat after accelerating up to speed. So you could go all day at 70 with the batteries gradually running down and the engine spinning at its most efficient providing the background thrust and the batteries filling in the balance of required power for fast acceleration and cruising, and being topped up both by regeneration and the diesel motor when you decelerate, stop, or cruise at a lower speed. And you wouldn't find yourself utterly boned if something went wrong with the battery system - you'd still have Fiesta Popular 900 levels of acceleration/hill climbing/max speed, albeit with Fiesta Popular 900 levels of Singer-like engine noise to go with.
(One may expect some concession to noisiness and fumes by the engine running down a bit or stopping entirely if you're doing less than about 20mph or pull up for more than 10 seconds)
Given that it doesn't necessarily need to run at all at lower speeds, it might even prove more economical in terms of weight and reliability/servicing to use a larger engine but without all the
-intercooler gubbins. If a 4-cylinder 1.7L-ish one can stick out 65hp, then a 3-pot (1.3L) plain diesel could manage 48hp peak (VW already made one with this output displacing 1.4L in the late 80s...), and a slightly chunkier 2-pot (with 1.0 capacity) could be high thirties. Again probably making around twenty with very good efficiency - certainly enough for a 90km/h cruise (even if not 100k) without increasing the engine throttle/rpm setting, or having to dip into the battery except for hill climbing and pulling away... and the level would then be made back up.
Charge it up at home, off the grid or from your own renewable sources, let the control system know roughly how far you plan to go/what route (so it can get an idea of what the power use profile will be and reserve enough battery to avoid racing the generator if there's a big motorway hill 20 miles before the finish) and how fiesty, laid back or parsimonious you want it to be, and off you go for what will hopefully be a three-figure MPG trip. Maybe stop halfway for fifteen minutes and plug into an EV point to juice it up a bit further without having to use more derv or have it chugging away whilst parked.
(Just a set of ideas that have been milling away in my head for a while; there are two, hard-to-blend approaches in "proper" hybrid design (ignoring all the stop-start and "tiny little booster motor" nonsense)... either having a small ICE that works moderately hard in concert with a decent electric motor so it never has to work -super- hard unless the battery is depleted (yer original Insight, Prius, and arguably the Ampera)... or a large one that only kicks in, with high gearing, once the car is up to speed or the battery is quite low, and cuts out at low speeds, so you have a decent amount of power on tap and a still pretty efficient cruising engine, that doesn't get used in its least efficient mode, ie creeping through traffic. A bit like the two approaches to economy cars - the 2CV route, with a weedy engine that would be more at home on a bike that you're *supposed* to drive in a fairly conservative manner, so it's always in the moderately-high percentage of max output zone that gets you the best HP-hour/kg of fuel... and what I will, for want of a better term, call the Vauxhall route - putting a comparitively large but detuned engine into the car along with high gearing. Even with your foot down it can't use too much fuel because of the limited HP, but it has tons of torque encouraging you to kick back in top gear, with wide-ish throttle and low rpm, cruising at speed very efficiently with power to spare. Each has a trade-off - the 2CV is underpowered and both uncomfortable and thirsty at speed, and the Vauxhall is unengaging to drive and thirsty around town. The two hybridisation modes counter each of those faults.
Now, if only we could find some middle ground that would work well ... I think the medium size diesel that runs as a constant generator thing may work as a strange blend of both?)
Though really, for heaven's sake, let's get hydrogen fuel cells working already. I'd certainly be up for it, if for no other reason than that they don't, AFAIK
, suffer the usual problems of being repetitively used at high power for extended periods from cold that both ICEs and battery electrics do - that plus they can be easily fuelled from completely renewable resources, the fuel can be generated well in advance and easily stored, it's not really any more flammable in an accident than a bunch of batteries, you can fill up quickly and go further on a fill, there's no fade effect, much of the required infrastructure is already in place, the cars will be lighter and therefore faster / go further for the same motor power and overall energy use, etc...
As for the Twizy itself ... it's a strange idea. Certainly carves a better niche for itself than the Aixam, GWiz, etc, which outside of London (and France or India) are cars looking for a purpose in a world much different from the one that spawned them and that they are poorly adapted to. Even on an afternoon's test run in a somewhat more capable Smart ED, I found it poorly adapted to the typical needs of someone running various errands in and around Birmingham (never even straying outside of the motorway "box"). The limited top speed was a pain on even brief (<10 mile) motorway and fast dual carriageway runs, the motor overheated quite readily when run continually up against the limiter and then pushed through a few stop-start lights on national-limit roads that would be unacceptable in any ICE car made after about 1970 (said overheating then causing the controller to progressively rob it of more and more of it's already just-about-adequate 40bhp), and even just on an errand that took from a base somewhere in an "8 o clock" suburb, into the middle of town, up to 12 o clock and then back round to 8 on the motorway, there was a serious case of battery anxiety going on, which turned into one of brinksmanship as I also had to be back by a certain time.
The Twizy's speed is even more limited, but then that may encourage you not to take on quite the same tasks as you would in a car. Sort of like being a slightly quicker moped; a C90 which won't fall over as easily in the rain. I forget what the range is but I think it was about the same as the Smart. Even if it was to run out on the way back, I would at least then have been on the surface roads through the middle of town and could more easily have got assistance. It's narrow so it can squeeze through traffic gaps more easily, e.g. the three-quarter-car-width where three lanes are opening up into four at a set of lights and no-one else thinks they can get through, but you can. Short and easy to see down both sides of for parking, etc.
I'm not convinced on the practicality vs cost front, but hey, if people can drop thirty grand on a "real" car, or six grand or more on a fancy motorbike, then they may be up for something like this. Especially if the running costs turn out affordable with the battery rental included.
I've been in a dealer which had a Twizy, and a Fluence, apparently both ready-to-run demonstrators (I didn't have the time, sadly), and they look like quite solid, usable machines, and the Fluence in particular has properly gorgeous styling for what is ostensibly a Focus rival. I can see them selling. The Twizy maybe to a particular type of urbanite who just wants something to spin down to the shops in to pick up a few backs of groceries and occasionally transport a tall pot plant, doesn't have much in the way of parking opportunities, and won't ever leave anything "in" it... and can't be having with the hassle of getting a bike license, buying the protective gear, figuring out how to load the shopping and plant onto the machine etc. It's sort of like a Reliant Robin turned inside out...
I'm interested, but, first, knock a couple grand off the price, make it hydrogen powered (or maybe even using some kind of weird LPG cell), and give it the ability to run up to, say, 110km/h not 80, because this is the UK not France and it's not having to deal with weird microcar / VSP / quadricycle laws. With that amount of aero drag, the current light quad regs should allow it plenty enough power to hit the 65-70mph zone, which is certainly fast enough for anything you'd want to do with it and wouldn't cause any hold-ups on the open road... plus it'd accelerate very smartly with the extra oomph. Performance would probably be then akin to my 125 bike instead of a C90 (...or a moped for the lower-output model), but without the risk of stalling off the line if you get it badly wrong, the need to shift gears, keep the engine buzzing, and change the
every 1500-2000 miles. And it'd have a rain cover and wiper - very welcome in this climate. It'd probably even have half a chance of fitting in my garage sideways on behind the Clio if they did the smart thing and gave it the ability to tuck its wheels in when you're parking it.