# Setting Up and Operating Electric City Buses in Harsh Winter Conditions
## 2 Theoretical Background
### The Effect of Ambient Temperature on Electric City Buses' Electric Consumption  
It is already widely communicated that the range of electric vehicles varies with temperature [31]. Research results also confirm this observation. For example, previous studies have shown that the range of electric buses decreases a lot as the temperature drops below zero degrees [32]. This happens because the functioning of the lithium-ion battery varies with temperature [14]. In 2015, [PERSON] et al. [33] studied public electric bus energy consumption during the coldest months in Latvia (Jan-Mar) and found that the bus consumed 2.86 kWh per kilomet. In 2015, a study estimated that an electric bus with a light aluminium chassis (9000 kg curb weight) consumed on average 1 kWh/km [34]. Electric Commercial Vehicles project (2012-2016) reports that the voltage drop caused by the internal impedance and the applied current at cold temperatures is the reason for reduced battery capacity [8]. In addition, [PERSON] et al. [32] report that temperature drops from around 10.0 \({}^{\circ}\)C to around 0 \({}^{\circ}\)C caused battery-electric buses to lose around 32.1% of their battery capacity. Another study found that ambient temperature impacted energy consumption a lot in the case of a DC/DC-converter, heat pump and drive motor [35]. However, power steering and an air compressor did not have an insignificant impact.  
Ambient temperature and several other factors influence the range of electric buses, such as topography, the road pave (sand, concrete), and the road's surface conditions (wetness, snowfall, sheet, ice). [PERSON] and [PERSON] [36] studied the relationship between ambient temperature and demand for heating power. They found that traffic congestion can result in a 60% overall increase in energy consumption. They also found that auxiliaries may consume 70% of the electric bus's energy during winter, whereas they generally consume almost 50% of total energy use [36]. In addition, the driving style affects the use of energy. For example, fast accelerations consume lots of energy [20]. Preheating the battery and indoor air before starting the bus, on the other hand, saves energy [16]. However, heating the bus cabin during the drive also reduces the range. Research shows that heating and cooling can consume 35% of all energy in electric cars [37]. While the energy consumption of an electric bus increases, the battery's state of charge and the travel range are reduced [38]. Therefore, researchers have proposed a fuzzy braking strategy of which electricity consumption was shown in a simulation platform to decrease by 9.8% compared to the normal braking energy management control strategy [39]. Then again, using a novel sorption air conditioner was shown to save cruising electric vehicles' mileage by 100 km [40].  
The bus body and insulation materials also impact how efficiently a bus passenger cabin is kept warm or cool, which again affects the energy usage of the bus [32]. For example, [PERSON] et al. [41] estimated that the average energy demand due to ambient heat loss of bus structure and opening the doors at the stops was 12-14 kWh. The bus was 12-m long, had 100 passengers and three doors, 150 kW electric traction motor and 33 kW installed power for the heating system [41].