4How 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 can power a typical conventional car? Assume:a.39 kWh of electricity are required to generate 1 kg of hydrogen in an electrolyserb.The energy content of hydrogen is 143 MJ/kgc.The energy efficiency of the fuel cells used is 55%, and that of the electric motors 85%d.The energy content of unleaded petrol is 34.2 MJ/litree.The conventional petrol car has an energy efficiency of 28%.
man are you way off. a 1 Kg of H2 contains exactly 33.1789 Kw-hr lower heating value of energy (from webBook.nist ). To make 1 Kg of H2 you will input 85 Kw-hr of electricity. Look up lower heating value and upper heating value, I don't have time to teach you everything. B, that is the upper heating value, why are you switching energy units, to confuse us and produce magic? lower heating value is 119.444 MJ/kg C the conversion rate of 55% is based on upper or lower heating value. Since a fuel cell CANNOT recover the upper heating value, your 55% is on lower heating value. D another slight of hand. The 34.2 in the lower heating value for gasoline. Lets keep it simple. The highest efficency H2 production units built require 1 BTU of natural gas to get .5 BTU of H2, thats 50% efficency. Multiply by .5 * .55 * .85 23.375% you A assumption is wrong, but lets go with that 39 kWh 140 MJ and you say in b, there are 143 MJ, wow, a 102% efficient system, that alone will save the world. Any way, 1.02 * .55 * .85 is a 48 % efficient system So you need 28/48 of the energy as a gasoline car would need. or 34.2 * 28/48 or 20.08 MJ which is 5.556 kW-hr. In real world, it will take about 12.5 kw-hr to replace 1 liter. In the US, 12.5 Kw-hr costs about $1.85 and a liter of gasoline costs about $.50, I'd rather use gasoline.
