One of the most significant 'construction sites' on the way to net-zero is transport. Electric vehicles are replacing combustion engines; public transport is expected to increase, while individual transport is expected to decrease. Buses are a particularly attractive option to expand public transport: Unlike rail, they require little new infrastructure. If motorized individual transport decreases with the expansion of bus capacity, there will be enough space on existing roads for additional buses.
To fulfill their mission of sustainability, buses must run on electricity, however. Today, diesel buses are increasingly being replaced by electric buses. But this process is only just beginning: In 2023, barely three percent of all buses on European streets were electric. 'If the bus fleet remains constant, it will take until at least 2055 before more than 95% of all European buses are replaced by electric ones,' says Harald Desing from the Technology and Society department at Empa in St. Gallen. 'That's after 2050, the year when Europe and Switzerland aim to reach the net-zero target - and many countries and regions have set themselves even more ambitious goals.'
In a publication recently released in the journal 'Environmental Research: Infrastructure and Sustainability,' Desing explored the potential of another way. 'By retrofitting existing buses for electric operation instead of replacing them with new ones, we can fully electrify the bus fleet around 15 years earlier - while saving emissions and raw materials,' says the researcher.
**Easy Conversion for Fewer Emissions**
As part of the EU research project 'CircEUlar,' Desing explored the potential of this so-called 'E-Retrofitting' for the European bus fleet in detail. His study shows: The conversion would be technically and economically feasible. 'There are already companies today offering E-retrofits for diesel and petrol vehicles,' says the researcher. The big advantage with buses is that the process and required parts could be standardized. 'Unlike the wide variety of cars, city buses have only a few model ranges, each produced in large quantities,' Desing explains.
The average lifespan of a diesel bus in Europe is about 20 years. The decommissioned vehicles are usually sold to other countries, where they continue to run for decades - and continue to cause emissions. 'That's not the most sustainable solution. Climate change doesn't stop at national borders,' Desing says. Retrofitting prevents the bus from continuing to run on diesel elsewhere - and the conversion itself causes about 20 to 50 percent fewer environmental impacts per bus than producing a new bus.
To convert a diesel bus into an electric bus, the engine and transmission essentially have to be replaced. Instead of an exhaust and diesel tank, batteries are installed. Any auxiliary drives for the air conditioning, braking system, and power steering can be relatively easily converted to small electric motors. 'With standardized retrofit kits, an individual conversion would take only a few days. The electrification of the fleet could thus take place without major impacts on ongoing operations,' the researcher explains. And: The parts removed consist largely of steel and aluminum and can be recycled.
**Faster and Cheaper to E-Bus Fleet**
Another benefit of retrofitting: Fleet operators wouldn't have to wait for the 20-year lifespan of their vehicles or artificially shorten it, but could undertake the conversion at any time. This could even extend the lifespan: 'Buses are replaced today because they no longer meet modern emissions standards, such as for particulates or noise,' explains Desing. 'When the drive system is replaced, the body and interior can often remain in service much longer.' Bus operators can thus save costs in the long term. Alternatively, these savings could be invested in expanding the bus fleet.
The additional charging infrastructure for electric buses was not the subject of Desing's study. However, the researcher is confident that it could be implemented relatively easily. 'In places with existing overhead lines, buses can be charged while driving,' the researcher explains. This would enable additional cost savings during retrofitting, as a smaller battery would suffice.
To pursue this promising strategy further, the technology for E-retrofitting would need to be standardized and scaled. Although he focused on the European bus fleet in the study, Harald Desing also sees potential for other countries and regions - although this would need to be investigated in more detail first. Retrofitting trucks, which still drive in larger numbers on the roads, would also be conceivable.
Media
Contact
Anna Ettlin
Communication
Tel. +41 58 765 47 33
redaktion@empa.ch