STM could save $3,500 a day with 100% electric bus fleet: Concordia study

A fleet of fully electric buses would allow the Société de transport de Montréal (STM) to save $3,500 a day, according to a study conducted by researchers at Concordia University.

The research team, led by Xuelin Tian, ​​who completed her doctorate at Concordia this year and is currently a postdoctoral fellow at Université Laval in Quebec City, is the first to conduct this type of study in a winter environment.

“The motivation for this study stemmed from the urgent need to decarbonize public transportation while ensuring reliable service in regions with demanding climatic conditions like Montreal, unlike other studies conducted in temperate climates,” she explained in an interview with The Canadian Press.

“The cold adds challenges by increasing the demand for heating the vehicle and reducing battery performance.” Slippery streets also reduce the performance of regenerative braking, which helps recharge the battery.

Thanks to connections established with the STM during previous research, his team was able to collect detailed data from 66,000 points across 56 routes operated by 40 fully electric Flyer XE40 buses.

The sheer volume of data collected is impressive. “We analyzed the records of approximately 50,000 trips in total, which is unique, thanks to the collaboration with the STM. We have never had access to such a comprehensive operational database before.”

More energy in winter

It will come as no surprise that electric buses use more energy in winter, that consumption is optimal in summer, and that spring and fall results fall somewhere in between. Thus, in winter, a battery electric bus (BEB) consumes 1.7 kilowatt-hours per kilometre, compared to 1.4 kilowatt-hours per kilometre in summer, representing a 26 per cent increase in cold weather.

Regenerative braking is also affected by the cold. The average recovered braking energy is 45.8 per cent, peaking at 50 per cent in summer and dropping to 32 per cent in February, typically the coldest month.

“Regenerative braking efficiency is greater in summer, but it is also linked to speed. The best regenerative braking performance is achieved with vehicles traveling between 30 and 50 kilometres per hour. At this optimal speed, 50 per cent to 60 per cent of the braking energy is recovered,” explained the lead author.

She adds that she was surprised that the incline of the routes – Montreal has no shortage of hills – has little influence on energy consumption. On reflection, however, this is an immutable law of physics: what goes up must come down. So, while energy consumption increases uphill, it falls below average downhill, and even better, the descent has a positive influence on regenerative braking.

Much cheaper than diesel

Where the study’s results become more interesting, however, is when compared to diesel buses. Operating costs for electric buses are on average 40 per cent to 60 per cent lower than those of diesel vehicles, both in summer and winter.

And what about hybrid buses? Their energy performance falls between that of electric buses and diesel vehicles.

“Typically,” the study states, “electric buses maintain the lowest operating costs, between $20 and $150 per day. Conversely, diesel buses have the highest daily operating costs, often exceeding $300, particularly in winter due to higher fuel consumption for heating. Hybrid buses fall into an intermediate category, with daily costs ranging from $100 to $250, offering savings compared to diesel buses, but far from the cost efficiency of electric buses.”

“Seasonal fluctuations are more pronounced for diesel and hybrid buses, while electric buses demonstrate stable year-round performance, thus demonstrating their economic advantage.”

Tian acknowledges, however, that there is a significant obstacle to conversion. “Obviously, these buses are very expensive. Government funding is crucial, both for the STM and for users.” Indeed, the Flyer XE40 costs around $1 million per unit, while a diesel bus sells for around $750,000 — a significant difference.

The STM has only just begun purchasing 100 per cent electric buses and its goal is to have a fully electric fleet by 2040, with the purchase of 140 vehicles per year. This fleet renewal should ultimately reduce the STM’s greenhouse gas emissions by 80 per cent.