Volvo announced that its three Plug-in hybrid buses that have been evaluated in Gothenburg, Sweden since June reduced fuel consumption by 81%. Of course, as they use less fuel and consume some electric energy, the resultant use of energy is 61% less than a diesel bus Euro 5.

Current collector on the roof of Volvo Plug-In Hybrid Bus

Current collector on the roof of Volvo Plug-In Hybrid Bus

Plug-in hybrid vehicles are unique because their energy consumptions depends on a ratio of EV mode versus hybrid mode, which depend on route and infrastructure.

We don't know for sure, but maybe Volvo's battery pack in the bus has 10 kWh of energy. Recharging takes place at the terminals via a current collector mounted on the roof. Only 5-6 minutes are needed to recharge, so even at 10 kWh must put out approximately 100 kW of power (if we assume that 6 minutes is a full recharge).

In Gothenburg, to lower energy consumption by over 60%, buses are driving in EV mode most of the route - for about 85% of distance. The remaining 15% is when the diesel engine kicks when the bus needs some extra power (parallel configuration) or the battery is depleted. Volvo is saying that this exceeds expectations.

Johan Hellsing, who is the Project Manager for the field test at Volvo Buses said:

“Our performance results are even slightly better than we had anticipated. The plug-in hybrid consumes less than 11 litres of fuel for every 100 kilometres. That's 81% less fuel than the equivalent diesel bus consumes.”

Volvo Plug-In Hybrid Bus

Volvo Plug-In Hybrid Bus

If 11 liters per 100 km are 19% of conventional bus, then a conventional bus on the same route must be using around 58 liters. This seems rather high for this size of bus in Europe, but the press release indicates that this particular route has many long, steep gradients.

The question that remains is if the savings of energy will offset the difference of the more expensive plug-in version and the expense of building the special infrastructure.

To date, Volvo's plug-in hybrid buses in Gothenburg accumulated 10,000 operating hours. Series production of these plug-in buses should begin in 2015 and Volvo already has signed contracts to supply the buses to Hamburg and Luxembourg.

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