It could be that the Airlander does not need to carry a lot of batteries. If solar cells are just enough to power the front fans, then it can run on these during the day and the diesels at the back at night. Relatively small battery packs at the front motors would be required for power during take off and landing.
The main advantage of electric power is that it allows the ducted fans to operate in any attitude, up to and beyond vertical, which aids getting airborne. if this was required from the current car-derived diesel engines, re-certification may be necessary. Vectoring the fan has got to give more vertical thrust than the current vanes in the prop wash, however good they are.
It is worth noting that the Airlander 10 is intended to lift 10 tons on 1400hp, whereas the Lancaster carrying the Grand Slam bomb needed 4 x 1620 hp to get itself and bomb airborne. How the range of the two compares, at max takeoff weight, would be interesting..