A physical model always assumes idealized conditions (driving on a flat surface, constant wind, etc.). Reality on the road is more complex. Here are the main physical factors for deviations and how you can simulate them in Watttrip.
Many believe cold weather primarily affects the battery. However, an often-underestimated factor is aerodynamics: Cold air is denser ("thicker"). At -10°C, the car has to displace significantly more air molecules than at +30°C in summer. In physics, air resistance is calculated using this formula:
F_L = 0.5 * ρ * cw * A * v²
What do these letters mean?
How to test it: Go to the Detail Calculator and change the outside temperature from 25°C to -10°C. Check the KPIs (below) for the "Air Resistance [N]" value. It will increase significantly because Watttrip converts the real temperature into air density ρ.
Every extra kilogram (passengers, luggage) must not only be accelerated when starting but also pushes the tires harder onto the asphalt. As a result, rolling resistance increases linearly with weight:
F_R = c_R * m * g
What do these letters mean?
How to test it: In the Detail Calculator, change the "Number of People" (the tool calculates 80 kg per person). Observe the "Rolling Resistance [N]" in the KPIs and the purple "Roll" path in the flow chart. Both will increase immediately.
When looking at consumption data, people often only consider the average speed. But an average of e.g. 100 km/h can be achieved in two very different ways: Either driving constantly at 100 km/h with cruise control (extremely efficient), or constantly accelerating to 150 km/h and then braking hard down to 80 km/h because of slower cars.
These constant, heavy accelerations demand extreme power peaks from the engine. A combustion engine is often pushed out of its optimal efficiency range (injecting disproportionately more fuel), and during subsequent braking, the hard-earned kinetic energy is simply converted into useless heat at the brake discs. Even in an EV, thermal losses in the battery and motor increase during constant full-throttle sprints, although it recovers a large portion when braking.
How to test it in Watttrip: That is what the "Max. Speed (Trip)" field is for. If you have an average speed of 100 km/h and increase the "Max. Speed" from 110 km/h (very steady driving) to e.g. 160 km/h, the mathematical model recognizes that you are accelerating and braking hard. It calculates a dynamic Peak Factor in the background, translating power peaks and the associated friction and braking losses into a noticeably higher consumption.
In a combustion engine, heating is "free" because a massive amount of unused waste heat is generated (anergy). An EV is so efficient that it produces almost no waste heat – the heating (PTC heater or heat pump) must draw power directly from the battery. At sub-zero temperatures, heating the cabin alone can require 3 to 5 kW of power. Especially in slow city traffic (where travel time is long), this drives up the consumption per 100km significantly.
How to test it: Watttrip features an integrated dynamic heating curve. At 20°C, the model assumes ~1.2 kW for AC & electronics. If the temperature drops to 0°C, this value jumps up. Look at the red line "Board/AC" in the flow chart. It gets significantly thicker in the cold!
If you are stuck in stop & go traffic, you are driving slowly (which is theoretically good for air resistance), but destroying any efficiency. A combustion engine continues to idle during standstill, burning fuel without covering a single meter. The EV, on the other hand, stands silently and uses power almost exclusively for heating/AC or the radio.
How to test it: Use the "Traffic" dropdown. If you set it to "Stop & Go", Watttrip calculates a massive idle consumption penalty for the unavoidable standstills of the combustion engine.
Driving uphill requires a massive amount of energy to lift the car upwards against gravity. This builds up so-called potential energy:
E_pot = m * g * h
What do these letters mean?
Although EVs recover part of this energy when driving downhill, charging losses of about 20-30% occur during the power conversion (Motor -> Inverter -> Battery -> Inverter -> Motor). Therefore, consumption on a mountain trip is always higher than driving on flat terrain, despite recuperation.
Important note on the calculator: Watttrip currently calculates a trip on flat terrain (sea level). If you drive from Munich over the Brenner Pass to Italy, your actual consumption will be higher than the tool predicts due to the elevation gain you have to overcome.