THE INTERNATIONAL REPORT
DAIMLER REVEALS E-MOBILITY
Alternative fuels were recurring topics in the recent major Busworld exhibition in Kortrijk, Belgium. There is now an unprecedented situation where not only traditional bus manufacturers are offering options to their well-established diesel ranges, but there is a new challenge from specialist battery manufacturers who are developing buses to use their products.
The latter are on a very steep learning curve, but they are helped by the availability of proven construction and drive systems. Two examples are Alcan’s aluminium-framed bodywork and ZF’s electric drive axles.
When I talk to friends in Daimler Buses, they sometimes lament that their company appears to be slower than others to develop new alternative technologies. While some competitors have been developing and promoting hybrid and electric buses, Daimler has been satisfying current transit bus demand with typical efficiency and success.
The company has already sold more than 5,000 Mercedes-Benz Citaro buses with the latest Euro VI diesel engines. Their tailpipe emissions are remarkably clean, and fuel economy is up to 7-8 percent better than on previous models. However, the company is not resting on its laurels.
In a high-level debate for manufacturers at Busworld Kortrijk, Thomas Tonger, Product Planning and Management, Daimler Buses, lifted the lid on his company’s proposed future developments. He described the latest Citaro with either diesel or CNG engines as nearly emission free. The full size plug-in hybrid bus is only partly emission free. Daimler’s preferred route was to go to zero emission driving for city traffic using E-CELL and F-CELL vehicles. He predicted that, in 2030, 70 percent of city buses sold in Western Europe will have a zero-emission drivetrain.
It might surprise you to learn that Daimler Buses has been active in electro-mobility for more than 40 years. The first electric test bus was built in 1969 and the first electric hybrid bus in 1978. The first fuel cell bus, known as the NeBus, was running by 1997 using an early Ballard fuel cell pack. To the best of my knowledge, these were used internally for research and development.
Fuel cell development has progressed rapidly, especially in downsizing of the stacks without any loss of power.
NeBus was followed by a fleet of 36 fuel cell buses which entered service in 2003 and 2004, three in each of 12 cities, mainly in Europe. They accumulated more than 2.15 million km. They ran in a variety of climates, from very hot to very cold, and in different terrains. Safety was paramount, so that if a serious fault occurred in one bus in one city, all the others were taken out of service as a precaution until a remedy was found. The fuel cell buses were popular with drivers and passengers and produced a large amount of valuable data. This included various methods of producing hydrogen.
The third generation followed in 2009 and the 23 buses of this type have accumulated more than 1 million km in service, in Germany, Italy and Switzerland. There has been considerable development in fuel cells, so that they are now smaller but just as powerful as the earlier generations. They use less hydrogen, therefore fewer storage tanks are required on the roof of the vehicle.
The most important difference between the second and third generations was that the former were not hybrid. This made it easier for engineers to assess how the fuel cells and generator were working and to identify any fault. The third generation buses are hybrid and that helps with fuel economy.
The fourth generation of Citaro F-CELL buses is currently predicted for 2019-2021. One of the advantages of the current generation is that they have sufficient range for a full day’s operation. Furthermore, Daimler can collaborate with its colleagues in other divisions to share costs of research, development and manufacturing of fuel cells.
Tom Tonger’s presentation gave a clear indication that the E-CELL bus would require opportunity charging during the course of each day, and that it might be launched around 2019. This timing might well be inspired, because the development of all-electric buses is moving fast and much of the technology is at a pre-production stage. Furthermore, other divisions in Daimler are working on electric vehicles.
While regular top-up charging greatly reduces the weight and size of batteries, it adds to the time spent at each end of a route and that can be a problem if a bus has been delayed in traffic. There have been reports of two or three buses waiting to use a charging system. That kind of delay can potentially lead to the requirement for an additional vehicle or two, and additional drivers, on a route.
On the other hand, if a vehicle is to have sufficient range for a full day’s operation, then the weight of batteries can be a penalty in terms of the total number of passengers that can be carried. BYD has demonstrated that its latest batteries are now two thirds of the weight of the previous generation, but still offer the same daily range.
If that kind of development can continue, it looks very promising. It might mean that buses do not have to be recharged every time they reach a terminus, but only a few times each day, using batteries with more storage capacity but without a weight penalty. There is also the option of opportunity, inductive charging from beneath the bus and that system can be used easily by other electrically powered vehicles, like taxis and municipal vans and trucks.
RATP, Paris, plans that 80 percent of its 4,500 buses will be all-electric by 2025. They have ruled out the possibility of opportunity charging, saying that it would be impractical and very expensive over such a large route network with so many vehicles. Paris has a significant number of bus routes which terminate at metro or heavy -rail stations, also dense traffic that can delay buses on route.
There are quite a number of other reasons why the timing of the introduction of the E-CELL and F-CELL models might be well calculated. Towards the end of 2015, the third SAENA (Saechsische Energieagentur) Conference was held in the German city of Dresden. This was largely a domestic event, where 26 speakers gave various accounts of the operation of all-electric buses in their cities.
In many cases, there has been political pressure to use zero-emission buses and transit authorities will only learn about them if they have practical experience on the streets. Reports were quite mixed, with electrical consumption being considerably higher in winter conditions, where heating is required.
On the relatively small scale of trials in Germany and other European countries, the electricity grid is capable of recharging battery buses overnight, and where necessary during the day. It will be a challenge when whole depots are converted to the operation of battery buses, with demand for large supplies of electricity overnight.
Currently, the manufacturing and transit industries are banking on the higher purchase price of electric buses being recuperated over a five to six year period by the much lower costs of electricity. There is a risk, probably quite remote at this stage, that governments will seek to recover the loss of taxes on fossil fuels by raising taxes on electricity for vehicles.
Major companies with vast electrical engineering experience, such as ABB and Siemens, are also becoming active in electric bus projects. One of the challenges for the industry is to ensure compatibility of systems between different makes of vehicles, so that recharging becomes as simple and universal as refueling with diesel.
The development engineers at Daimler will be following progress on all these issues with keen interest. The E-CELL and F-CELL models will have to be ready for volume production and sales, which makes introduction in 2019 an interesting challenge.
Doug Jack is with Transport Resources in the United Kingdom.