In today’s blog I have borrowed a lot of the material from my group mates Johan Larsson, Magnus Broback and from our manager, Jessica Sandström.
Volvo Buses has gained experience of charged electric buses, since the introduction of the Sunwin (Joint venture in China with 50% Volvo ownership) Super Cap bus in 2006.
Super capacitor since 2006.
Fast charging at every bus stop for 40 seconds. The system has challenges with high infrastructure cost and low energy storage capacity.
Battery electric buses since 2010.
Battery swap system: The system has challenges with: Low battery utilization and time loss when swapping.
Battery overnight charging: The system has challenges with: Limited range and heavy and expensive batteries.
Volvo 7900 Hybrid was an in-house development and the first automotive application using lithium-ion battery technology. Volvo has more experience in automotive battery and control technology than any other HD automotive manufacturer.
When comparing opportunity charging to overnight charging, then the high utilization of charging infrastructure and the limited battery weight in the opportunity charging concept makes it superior in cost efficiency compared to overnight charging.
Opportunity charging has “unlimited” daily mileage giving high fuel saving.
The opportunity charged buses can be used in slow and rapid bus routes. By increasing the speed of the buses it:
- saves times for travellers
- gives higher passenger transport capacity.
Overnight charging limits the daily range and the passenger capacity.
In dialogue with cities I have found that some bus routes are today limited to less than 200 km and thus potential routes for overnight charging. Still, the ambition of the city is mostly to raise the attractiveness by higher speed and higher capacity. To go for opportunity charging is thus a future safe choice.
Each bus route has characteristic power consumption and it varies with the climate.
The system design needs to handle different routes and climate. I have been in dialogue with many cities to analyzing each route in the city to determine their specific needs. Again, mostly we find that opportunity charging and the battery buffer used, account for all eventualities.
Opportunity charging is ideal for electric supply by solar and wind
Many cities have decided to decrease imports of fossil energy and to increase local and sustainable electricity. Opportunity charging makes sense, to utilize the energy when it is most available.
To conclude, all types of electric buses utilize much less energy than diesel or gas alternatives. The longer the daily distance, the stronger the benefit.
Compromises are needed:
Passenger capacity <-> Battery weight
Driver/bus utilization <-> Charging time
Cost for fast charging stations <-> Battery cost
We find that:
– High utilization of charging infrastructure and the limited battery weight in the opportunity charging concept makes it superior in cost efficiency towards overnight charging.
– The opportunity charging concept allows 17% more passengers.
– Overnight charged battery buses are convenient for testing the new technology in small scale, but have strong limitations in the daily range. This restricts it to slow routes, therefore with limited benefits.
-The opportunity charged buses can adapt to long workdays, high passenger capacity and high mileage. Thereby they deliver strong benefits for the city.
In the choice between different types of electric buses this is why so many cities now inves in opportunity charging infrastructure:
– The city wants to incest in a system that is future proof for increased mileage and speed.
– The city wants to secure transport/passenger capacity.
– The city wants to secure a reliable battery system that minimizes the risk of the investment (Volvo Turn Key solution allows cities to pay by the kilometer).
– They want to reach out to all routes, longer and faster transits as well as the down town business district.
– The city wants a local energy source and buses energy use that match the supply by renewable energy.
– The cities have analyzed the bus traffic pattern and found that the bus stops at the same spot every now and then for several minutes and wants to take the opportunity to charge the batteries to prolong the life and extend the distance.