The dream of electric vehicle

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To travel 100 km in a normal driving style, a 1500 kg car needs about 20 kWh energy. Careful drivers can reach 100 km with 16 kWh and sporty drivers can go up to 25 kWh. The car energy is stored in gasoline or diesel and one liter of gasoline consist of 9 kWh energy. Having a full fuel tank of 40 liters the total energy available is 360 kWh (this amount of energy is consumed in one year by a modern fridge). To produce mechanical power out of gasoline energy, we have the Internal Combustion Engine power train efficiency transformation of about 28% (most of the energy is lost by heat during combustion). Doing the math, out of 360 kWh we get 100 kWh mechanical energy and this provide a range of 500 km (average consumption of 8l for 100 km).

40 liters of gasoline provides 500 km range for a conventional car.

A very good Li Ion batteries (Panasonic 18650 or 2170) has volumetric energy of 0.6 kWh per liter, 15 times less than gasoline. To produce mechanical power out of electric energy, we have the Electric Motor power train efficiency transformation of about 90% (only 10% is lost by heating and magnetic field). To store 20 kWh mechanical energy (the equivalent of 100 km range) we would need 37 liters. The electric power train is assumed to have the same mass as ICE power train.

In the same fuel storage volume, electric cars have only 100 km range.

To increase the autonomy of an EV to 500 km we would need 110 kWh LiIon battery.The calculated volume is 183 l and with specific density of 0.25 Wh/kg* we get 450 kg for the battery pack. Let’s consider also the battery electronics, each LiIon cell requires voltage/temperature monitoring. Using the example of Tesla S, with 13.5 Wh energy on a cell, we get 1666 cells for 20 kWh and 8148 cells for 110 kWh, so the electronics will add some additional mass.

*The volumetric or the “gravimeter” density of 18650 batteries is higher compare to prismatic cells used on Leaf, iMiEV, Zoe, Kia EV, eGolf with values in the range of 0.1 kWh … 0.15 kWh).

To have 500 km range an Electric Vehicle require 500 kg Li Ion battery.

Would you still need 20 kWh energy to drive 100 km? An educated guess will be NOT. Having a car with 2000 kg, the requested energy will increase to 25 kWh per 100 km, remaining then only 300 km range.

Related to autonomy, an electric car can reach same driving range as conventional car by increasing the battery mass. But, to keep weight under control the car manufactures shall find ways to reduce the overall mass of the vehicle or to use lighter but more powerful LiIon packs. The good news is that each year the volumetric energy is increasing with 10% and the process will speed up if EV cars will be sold in big volumes.

According to Tesla, the price of 1 kWh LiIon storage is about 273 so a rough estimation for 500 km range is 30.000€, for the battery. Do not expect this to be the price paid by the final customer but let’s keep the optimistic approach. In comparison to conventional car, the storage tank for 40 liters gasoline cost maybe 50€? including fuel level detection and electronics. For the active energy, the price for domestic 1kWh is 0.

To reach acceptable price for end customers, the OEMs reduced the range of EVs to 100km to 200 km, but this mean they sell small volumes of such cars. Till 2016, 2 Mio EVs were sold world wide, compared with 93 Mio ICE car sold only in 2016. However, it is expected to reach even number of sold cars in 2039 and in 2030 the price of 1 kWh LiIon storage to be 73€. Bloomberg cite.

Waiting timeRecharge waiting time for actual EVs with 20 kWh battery is 30min but only if the charging is done at 50kW station. And you get 100 km driving pleasure. For 500km you will need 2.5h or to charge in 30min from a 200kW station. That’ huge but guess what? Tesla is proposing already this 50kW level for charging stations. It’s easy to understand why