“Only 1.35 kWh/kg H2 is required for compression to 700 bar, with an additional 0.12 kWh/kg H2 to reach a refueling pressure of 880 bar.”
https://www.hydrogen.energy.gov/pdfs/9013_energy_requirements_for_hydrogen_gas_compression.pdf
As stated earlier on Kg of H2 has the energy of three gallons of petrol. 20/3*1.35 is about 9 kWh those 6.66 kg of H2 have 798.91 MJ of energy to the LHV. 9 kWh is 32.4 MJ or about 4% of the lower heating value when burned. The catch is hydrogen used in a vehicle will be with a second law of thermodynamics fuel cell not a first law combustion engine so in that case the HHV or higher heating value is used since no combustion is done and the raw chemical energy is available 6.66 kg has a HHV of 944.92 MJ so in a fuel cell car the compression energy is 3.6%
Not really a factor in the overall scheme then. Thanks for the breakdown