Does regenerative braking, using supercapacitors, really save fuel in the case of diesel city buses?
A 10-ton diesel bus, fully loaded, that slows down, on average, from 30 km/h to 0 km/h each minute and keeps like this for 18 hours per day loses a total of kinetic energy:
60min * 18h * 10000kg *((30km/h)^2)/2 = 104kWh
104kWh is enough for that bus to run for 1 hour at 30 km/h, fully loaded.
In other words, each 18 days such a bus, using an efficient regenerative braking system with, say, supercapacitors, can not save more than 1 day of continuous run for 18 hours, assuming all conversions are 100% efficient. If the overall conversion has an efficiency of only 50% (a more realistic case) the bus will have to run 36 days to save 1 day (18 hours).
For me, it seems that the regenerative braking is not worth the effort (supercapacitors plus an electric motor / generator plus other mechanical complications which increase the cost of the vehicle and the maintenance expenses).
Is my evaluation correct or I am missing something?