*4.7. TCO for Combustion Engine Buses*

We have now defined equations for the nine TCO parameters for two types of electric buses. In order to better interpret the variations in the TCO for these two types of electric buses, they will be compared with the TCO for combustion engine buses. We use the same way of determining the TCO of the electric buses based on the nine TCO parameters, with different values of most parameters. Since there is no need for combustion engine buses to charge, we can analyse them only based on the trips they drive and driving to and from the depot, as illustrated in Figure 11.

$$N\_{\text{BusTotalICE}} = N\_{\text{BusPeak}} \tag{48}$$

$$T\_{\text{ChgTotalICE}} = 0,\tag{49}$$

$$\mathcal{W}\_{\text{BatteryKE}} = 0,\tag{50}$$

$$N\_{\text{CHgTotalICE}} = 0,\tag{51}$$

$$P\_{\text{ChgTotalICE}} = 0,\tag{52}$$

$$N\_{\text{ChgPlacesICE}} = 0.\tag{53}$$

**Figure 11.** How the use of buses with combustion engines varies during the day.

Trip distance is the same for all types of buses, as it is determined only by the timetable and route. The total driving distance, traction energy use, and trip distance are calculated in the same way for combustion engine buses as electric buses, but with the difference of being based on a different number of buses during the peak time and midday.

Instead of calculating the cost of electricity, the energy cost of the combustion engine buses will be the fuel cost, which is determined from the required traction energy, just like for the electric buses. The cost parameter for the fuel takes into account both the fuel cost per litre and the fuel consumption per kWh of traction energy, i.e., there is no need to calculate the fuel consumption in litres explicitly. The fuel cost of HVO buses used in this paper is 3.5 SEK/kWh for traction energy, and 4.0 SEK/kWh for biogas. They are based on prices from Reference [1], which indicates a HVO price of 1.46 SEK/kWh and a biogas price of 1.25 SEK/kWh, and this paper has assumed an average powertrain efficiency of 36%.

Chargers are replaced by one fuel station at the depot. However, many bus routes share the cost of the fuel station, so we assume the investment cost of the fuel station to be included in the fuel cost per litre.
