Unique study by TNO of the performance of zero-emission buses

22 Sep 2014

In 2025 the five thousand or so public transport buses will no longer produce harmful emissions. That is the deal made between the government and Stichting Zero Emissie Busvervoer. To achieve that target many technical questions have to be answered, so the Ministry of Infrastructure and the Environment has asked TNO to study the actual performance of electric-powered buses.

TNO noticed that there were many questions concerning electric transport among the authorities and public transport concession granters. Much was already known about the emissions and fuel consumption of cars and trucks but zero-emission buses are quite a different matter. In urban areas certainly speed is continually changing, there is constant braking and accelerating, doors opening and closing, heating and cooling. 'So the questions that needed answering were how electric-powered buses actually perform on the road, what is the actual range on one battery, how does consumption vary when circumstances change and how energy-efficient is a hydrogen-powered bus? Manufacturer specifications, TNO had already found, tend to be much more optimistic than actual facts when it comes emissions and consumption. So we subjected the buses to a series of extensive tests. This generated a unique treasure trove of useful data for all of those involved in public transport,' TNO expert Gertjan Koornneef.

Evaluating deployment

Many relevant performance parameters were measured and calculated on the basis of field tests. First of all, TNO had to design the test method. In the world of bus transport procedures were in place to measure the fuel consumption of diesel buses but not for electric buses. Two bus concepts have been tested in practice: hybrid buses (electric plus fuel) and buses powered by various types of battery. Later this year tests are scheduled for a hydrogen-powered electric bus.
Koornneef: 'The results of the tests give the authorities and bus companies insight into how zero-emission buses can be deployed on their routes, from a vehicle point-of-view. These results are also important for the granting of concessions and, of course, for determining government policy and legislation.'

Minimum and maximum range

Within the electric, hybrid and hydrogen concepts, all kinds of variations are possible. TNO has tested buses with different types of battery, for example with a large battery that has to perform, in principle, all day long in both warm and cold weather, and smaller batteries that are able to recharge quickly a couple of times a day. The focus here lay mainly on those factors that affect energy consumption and, therefore, range.
'Not only did we measure the performance of the buses but we also made calculations. Everyone knows that using the air-conditioning or heating has an impact on the energy consumption but we ascertained that in extreme cases this uses just as much energy as is needed for propulsion. So, by quantifying everything, you can estimate the minimum and maximum range for a specific type of bus in particular circumstances for your urban and regional bus routes as well as optimise the energy consumption for zero-emission buses,' Koornneef concludes.

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