Question

How much electricity (in kWh) would be needed to produce the hydrogen to power a hydrogen-fuel cell car for the same total vehicle km as one litre of petrol in a typical conventional car?Assume:

a. 63.0 kWh of electricity are required to generate 1 kg of hydrogen a high pressure electrolyser and pressurised to 350 bar suitable for on-board storage in a mobile application.

b. The energy content of hydrogen (HHV) is 142 MJ/kg (~40 kWh/kg)

c. The average energy efficiency of the fuel cells used is 44% (based on HHV), and that of the electric motors 86%

d. The energy content of unleaded petrol is 34.2 MJ/litre e. The conventional petrol car has an average energy efficiency of 20% (see the lecture materials)

Answer 1

t1 litre of petrol = 34.2MJ of energy. But the energy efficiency is 20% => 1 litre of petrol effectively = 20/100* 34.2 MJ = 6.84 MJ

Let x be MJ of energy that comes from Hydrogen. Then taking efficiencies into account, x* 0.44*0.86 = 6.84

=> x= 6.84/ ( 0.44*0.86 ) = 18.07MJ

1Kg of Hydrogen gives - 142 MJ => 18.07MJ is obtained from 18.07/142 = 0.1272Kg

to generate 1Kg of Hydrogen - 63 kWh of electricity is needed

To generate 0.1272Kg of Hydrogen - 0.1272* 63 = 8 kWh of electricity is would be needed