*1.1. Di*ff*erent Types of Electric Buses*

Electric buses have a very low operating cost compared with conventional buses, but a higher investment cost of the battery and chargers, and sometimes additional cost of the driver waiting during charging and for extra buses required due to the charging time. It is not possible to minimize all these cost at the same time, so there is a need to find a cost-effective compromise, which depend on the timetable and bus route properties, and that is why several different charging strategies are relevant for analysis.

Charging at the end stops means that the buses can have smaller batteries than buses charged at a bus depot, as they can charge after each trip. This can be cost effective as long as there are many departures per hour, allowing the chargers to be frequently used. The chargers are used very little if the bus route has low bus traffic density, and a low utilization of the chargers increases the cost per trip kilometre. One of the drawbacks of charging at the end stop after each trip is that there is a need for extra buses to have time to charge.

The operators want to minimize the number of buses for a bus line since the investment in buses is a major cost driver. That is why the second charging strategy in this paper, end-stop charging off-peak, is included. All buses then drive during peak times without charging. Between the morning and afternoon peak times, typically 09:00 to 14:00, all buses are not needed in traffic, so then they can charge. This will reduce the number of buses, but it will also require bigger batteries onboard since the buses need to be able to drive for about three hours without charging. It is not obvious which timetables and bus routes that could make one or the other charging strategy more cost effective.
