When the Volvo hybrid double deckers, with bodies built by Wrights, were handed over to the London Operator Arriva it was also the launch for the Volvo hybrid double decker bus.
Arriva received 6 hybrid double deckers by Volvo. They will primarily be used on rout 141. As for the Single Decker (7700 hybrid) Volvo uses the four cylinder version of the D7 engine B5L. The Volvo in-house parallel hybrid technology, ISAM drive train, recuperates the brake energy to save fuel. The fuel saving will be likely to exceed 30% in the everyday use in real traffic.
The new bus has attracted a lot of attention. I have gathered some of the references below:
Recent Volvo Hybrid Double Decker references