Funny, it's using a lithium ion supercapacitor.
Self discharge is usually of the order of weeks to months, so Toyota must just have had an energy capacity issue (not surprising since they hold 25 times less energy than Li-ion batteries per kg - EDIT: this one's only 5 times less). Its trump card is that the charge / discharge power is ten times (EDIT: this one's only three times) that of any battery, which is excellent for maximising regenerative braking, but works fine at low powers too. Supercaps would work brilliantly coupled with a small battery, but that requires complex control which in racing is typically legislated to the hilt...
The 33 hp power rating given for the Sián is that of the electric motor; you don't add the rate you can fill your fuel tank to your car's power output, do you?
It's also only the power rating when used for acceleration; I'd wager it can be pushed much harder than that for short bursts, e.g. in braking...
Not sure I follow your thought process here. Yes it's lithium ion but supercaps are vastly different from regular batteries in the way they absorb and release charge.
Now I'm no electrical engineer, so smarter people please correct me if I'm wrong, but here's my general understanding:
Supercaps - high energy density but limited total energy content, high charge/discharge rate but cannot stop doing either midway (i.e. once it discharges it spends everything it has at once)
Batteries - lower energy density but higher total energy content, lower charge/discharge rate but more flexible discharge pattern (i.e. can discharge to say 50%, hold, and discharge a bit more later)
So even though the Lambo can charge to 100% and deploy all that charge quickly, it cannot store a lot of it and once it's gone, it's gone until the next heavy braking zone. If you're on a track with mostly high speed corners with no heavy braking zones, the system won't ever recharge to 100% and it's benefits will be minimal. Whereas a traditional battery hybrid supercar will still have some charge left and free to deploy it whenever, wherever in this situation.
I'm not talking at all about self discharge in terms of the power store losing electricity long term. Batteries lose a little charge when sitting there for long periods of time, but I'm not sure about supercaps.
As for the power rating, I'm not sure what the issue in my interpretation is. It's basically the extra power the system gives that can be put to the ground. I mean the motor is sitting in the gearbox itself. Can't get anymore direct than that. I just wonder how many people who buys the car will be able to tell the difference of extra 33 hp at full throttle, compared to say, Aventador SVJ given the similar performance numbers.
Don't get me wrong I love the car's looks and the novelty of supercaps in a road car, but IMO the system feels like a quick add on just to say "we've done a hybrid".