I've been curious about using a supercapacitor for energy storage for some time. I don't think the value proposition is to replace a battery for the same purpose, but perhaps in a similar location in the drive train, with a different function.
A supercapacitor charges and discharges very easily. Charge is stored as charge, rather than requiring chemical conversion to store energy and chemical conversion to release energy.
The contrast with a battery is that a battery must be large - not just to provide range, but also to allow maximum discharge current. How many "C"s are you willing to push your battery to in order to accelerate? If you keep the discharge per battery low, you need a larger capacity battery to source a given amount of current. That adds significant weight, and significant cost.
A supercap in a series hybrid would just function to provide power spikes at acceleration / deceleration, and keep the motor at peak efficiency.
I'm more interested in using supercapacitors as temporary energy storage, between a generator (or alternator with appropriate converter) and my electric traction motor. If I can supply the large current needed for acceleration and accept the large current generated with braking...that is the benefit.
This would need to be paired with an ICE or microturbine or free piston generator or... that would run near optimum efficiency to keep the supercapacitors at a programmed charge level.
I think that Ariel is working with Delta Motorsports on this sort of idea, and a couple of Chinese companies are as well (techrules comes to mind, but I think there is another that I can't recall at the moment).
Hypothetical (until I pull the switch
A tube frame car that weights 1700 lbs with low drag. Current versions use an ICE with a 160 HP engine and a 4-5 speed. The engine and transmission weigh about 205 kg (450 pounds). From my rough estimates, I could get a sufficient synchronous motor and gear reducer for 75 kg. Supercapacitor would weigh (much less than batteries) about 180 kg for 500V. I need a 20-30 kW generator. I could go wankel, microturbine, or freepiston...all of which are in the 15-20 kg range.
All told, on paper it looks to be about 75 kg heavier than the ICE version, with plenty of acceleration, optimum efficiency of the ICE, and no battery issues. Since an electric motor can be mounted transversely with gear reducer dumping power out on a parallel axis to the motor rotation, very low losses occur between motor and wheels.
Any thoughts on this sort of application?