# Setting Up and Operating Electric City Buses in Harsh Winter Conditions
## 4 Results and Discussion
### Monitoring and Estimation of Energy Consumption
Figure 9 shows electrical energy consumption as a function of temperature so that each blue dots represent one drive between the start and end station. Since 2019, it has been possible for the operators to choose between diesel fuel and electricity for heating the battery and the interior. The measurements show that most drivers had opted for fuel heating. This option was removed from 2020 onwards, and the fuel heater was controlled automatically; it was activated only when the ambient temperature was below -15 \({}^{\circ}\)C. This can be clearly seen from the figure. The figure also has a polynomial curve fit to data, which have been carried out in two separate cases due to the diesel heating. Below 0 \({}^{\circ}\)C, the fitting is carried out to temperature data between \(-15\) and 10 \({}^{\circ}\)C. At temperatures above zero degrees, a fitting was made to those values. The energy consumption (EC) is shown in Equation (1), where \(T\) is the temperature in degrees Celsius. \[EC=\left\{ \begin{array}{cc}5.4\times 10^{-5}T^{3}-2.7\times 10^{-4}T^{2}-0.05T+1.6,&T\geq\ 0\ ^{\circ}C\\ -0.04T+1.6,&T<0\ ^{\circ}C\end{array} \right. \tag{1}\]  
The graph shows that the average energy consumption increased by about 0.4 kWh when the temperature decreased to 10 \({}^{\circ}\)C. Air conditioning increases consumption when the temperature is above 15 degrees. Its effect is approximately equivalent to an increase in consumption at temperatures below zero. Figure 9: Energy consumption as a function of temperature (blue dots—samples; red line— polynomial curve fit). Two outlier groups are interesting: (1) Although there is considerable frost, there is small consumption, and (2) high consumption near zero degrees. A common feature of the first case is the short duration when doors are open, meaning few passengers and little heat escaping from the doors. There might be several reasons for the second group: snow, slush or slippery road. In any case, they have the doors open for a long time, indicating a lot of passengers. Table 1 shows energy consumption (kWh/km) for different cases for 2019 and 2020-2021 separately due to the change in the heating mentioned above. The data is the same as in Figure 9 except that the cumulative passenger entry and exit time shall be at least one minute. There are some high values for 2019 since the winter was rather cold and snowy. The highest six values occurred when the temperature was between \(-1\) and 5 \({}^{\circ}\)C. This reflects the fact that snowy weather, particularly snowmelt, increases consumption significantly. Winter 2020 was warm and had hardly any snow, but 2021 had cold and snowy winter. The median energy consumption was 0.8 kWh/km greater when the temperature was below zero than over zero. Again, there were some high consumptions near zero degrees, which can be observed from the figure. The median difference between driving the route when the snow was melting and without melting was 0.2 kWh/km. The distribution of melting cases was twofold: either it had little effect, or the consumption increased greatly. Understandably, a small melt has little effect, but if the vehicle is driven in slush ice, consumption increase considerably. The results show that the weather and climate affect the operation of buses and the entire electric bus system. Four electric buses travelled approximately 500,000 kilometres (2019-2021) using an average of 1.43 kWh/km electricity. However, this number also includes the energy use by cooling systems during summer and heating during winter, as they could not be separated in the monitoring setup. The average energy consumption during thermal winter was 2.1 kWh/km and 1.2 kWh/km during thermal summer. Thermal winter starts when the average temperature is below 0 degrees Celsius at least five days in a row. Thermal summer starts when the temperature is over +10 degrees Celsius at least five days in a row. In Tampere, the thermal winter was 7 December 2020-22 March 2021, and thermal summer was 10 May 2021-14 September 2021.