There is 35.8 Megajoules of energy in a litre of diesel, costing £1.20 (2017). Only 10.74 Megajoules of this energy is translated into useful energy at the wheels - about 10.74gajoules per litre.

Assuming the charging of an electric car is 85% efficient, We will need to supply

\[\frac{10.74}{0.85 \times 0.6}=20.61 \: Megajoules\]

of electrical energy for the car to have the same useful energy as a car with an internal combustion engine.In 2017 1 KWh electricity cost about 13p. A KWh hour is equivalent to 1000 W supplied for 3600 s, or

\[1000 \times 3600=3.6 \times 10^6 \: J\]

21.61 Megajoules energy is equivalent to

\[\frac{21.61 \times 10^6}{3.6 \times 10^6}= 6 \: kWh\]

which would cost 78p.Hence electric cars are cheaper to power.