cities buses

Alternative power sources for buses – now and in
the future
Franz Redwitz talks about electromobility in public transport
Tighter exhaust standards, stricter legislation and increased sense of responsibility for the environment are fueling the development of alternative
means of powering. Franz Redwitz, Head of Product Marketing Bus & Coach
at MAN Truck & Bus, spoke in the leadup to Busworld 2013 about the development of alternative powering sources for buses, pointing to the fact that
electromobility does not automatically mean ecological friendliness.
MAN Truck & Bus
Dachauer Strasse 667
D-80995 Munich
Corporate Communications
Dominique Nadelhofer
Phone +49 89 1580-2001
[email protected]
Bus Communications
Mr Redwitz, what kind of a role does electromobility play for MAN Truck
& Bus?
Ralph Korek
Phone +49 89 1580-63864
[email protected]
Electromobility is obviously high up on the agenda for MAN, as throughout
the vehicle industry. But you have to take a differentiated view of things.
Purely electrically powered buses are at present neither economical nor
ready to go into series. There are a number of reasons for this: For one
thing, operating electric vehicles efficiently calls for large investment in infrastructure. Then, also important, you have operational safety, cost and service
life of the batteries. The batteries available at the moment are very expensive, plus they need to be replaced every five to six years.
Not forgetting the extremely high weight of these batteries. Even the next
battery generation won't match diesel or gas in terms of energy density. I'll
illustrate it by a comparison: The energy density of a modern electrical battery is maximally about 150 watt hours per kilogram. A liter of diesel on the
other hand gives you 11,800 watt hours per kilogram. So you see, batteries
have a long way to go in energy density if you want to drive a city bus fully
electrically for a whole day without any interruptions. The alternative is either
very high vehicle weight, or a special and pretty complex infrastructure for
recharging in between.
But the biggest challenge posed by electromobility is probably safety. Batteries consist of single cells that have to be combined into packages. The result
needs to be absolutely safe because you can't have an electric bus that's in
any way less safe than a diesel or gas powered bus. Batteries must be in-
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stalled and safeguarded in vehicles to prevent them exploding or releasing
harmful substances into the environment in case of a defect or accident, for
instance. That means another increase in vehicle weight.
There's a bigger demand emerging for emission-free zones in cities.
Isn't complete electrification an especially environment-friendly alternative for public transport?
There are different aspects to that kind of argument. The bare facts tell us
that an electric vehicle isn't automatically efficient or environment-friendly. In
Europe energy is generated from different sources and then mixed. If energy
won from wind power is mixed with current from coal-fired power stations, for
example, that also increases carbon dioxide emissions. Which means that
electric vehicles aren't the optimum way of reducing greenhouse gases.
A recently published study from DENA – the German Energy Agency – found
that biogas and electric power have an identically small carbon dioxide footprint. Taking the complete energy chain that's about five grammes per kilometer. But that only applies for two factors: The biogas must be produced
entirely from manure, biogenic waste material or waste water, the electricity
from purely regenerative sources. The study assumes this. The emissions
from all other types of fuel are 15 to 30 times higher. This isn't especially
surprising for conventional modes of powering. But it's often not realized that
supposedly clean fuels like ethanol or biodiesel cause substantial carbon
dioxide emissions.
Is going hybrid an alternative?
Yes, no doubt. In the MAN Lion´s City Hybrid we already have series produced and economical, future technologies up and running. In this way we're
constantly gaining experience in what's decisive to make electromobility efficient: in energy management onboard a city bus. With its serial hybrid drive
this low-floor bus saves up to 30 percent on diesel and CO2. While conventional buses convert their braking energy into heat – by service brake and
retarder – the MAN Lion's City Hybrid saves this braking energy in ultracaps
and transforms it into power to drive its two electric motors.
Another advantage of hybrid buses is the reduced noise. When pulling away
from a stop, the bus moves fully electrically. The diesel engine doesn't cut in
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until after a few hundred meters. That avoids bothersome noise where a
conventional bus causes most. The noise level in the interior is also extremely low.
Basically then, we're already offering a ready electric bus that can manage
without an internal combustion engine if, as the next step, you replace the
diesel engine by batteries or another energy source. A series hybrid vehicle
also presents the advantage of recharging during operation. In that way we
combine the best of two worlds. Experience with the MAN Lion´s City Hybrid
is very satisfactory: To date there are more than 200 MAN hybrid buses
working successfully in European cities.
What's the role of natural gas and biogas as alternative power sources?
In public transport you see an increasing number of natural-gas-powered
buses as an investment for the future, as an economical, environmentfriendly alternative to conventional diesel. Compared to other fossil fuels,
natural gas shows especially high CO2 efficiency. Natural gas also combusts
very cleanly, so engines emit low levels of air pollutants such as carbon
monoxide, hydrocarbons, nitrogen oxides and particulate matter. Using biogas, buses can even be operated CO2 neutral.
The price of natural gas is often lower than that of diesel fuel. Operators of
natural-gas-powered buses also frequently benefit from state incentives.
Given their very soft fuel combustion, CNG buses are especially quiet on the
When do you think we'll see fully electric buses in public transport?
Demands for purely electric operation of buses will increase. So there's no
getting around electrification, and longterm it will become a sine qua non for
all European bus producers. As soon as economical operation of fully electric
buses is possible – and there's appreciable demand for them – MAN will be
able to deliver.
In the Lion´s City Hybrid and a wide-ranging portfolio of CNG buses, MAN
offers CO2-efficient options as alternatives for the future of public city
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The MAN Group is one of Europe's leading industrial players in transport engineering with annual revenue of some € 15.8 billion (2012). MAN
is a supplier of trucks, buses and coaches, diesel engines, turbo machinery and special transmissions and employs 54,300 persons worldwide. MAN's business areas are all leaders in their markets.
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