After all it's not as if by 2040 all our electricity will come from green sources, lots of it will still be generated by conventional gas power stations
However, the BEIS projection is that the CO2 intensity of electricity will more than halve by the early 2030s*, so diesel trains will look very high CO2 compared to electric. If a CO2 price is applied to diesel, this would tend to push the case for electrification
*Page 36 of this doc.
https://www.gov.uk/government/uploa...ted_energy_and_emissions_projections_2017.pdf
Diesel fuel is 48MJ/kg and 38.5 MJ/l
Lithium ion batteries are about 0.5 and 2
I.e batteries are a very large and heavy way of storing energy compared with fossil fuels
This is, of course, entirely true - but it's a false comparison to make.
Firstly, electric drive efficiency will get you about twice as far per MJ than a traditional diesel engine
Secondly, you can get quite a bit of energy back with regenerative braking, rather than using rheostatic braking to warm up the sky (I've seen 17% for 390s)
Thirdly, there's no need to lug a diesel engine about, which on a 22X means >2 tonnes of battery before there's any weight penalty
And the final major point is that nobody would be expecting a BEMU to go 1-2 days between refuelling, you'd use them on routes where they could be recharged from existing electrification.
Back on topic - the above is relevant because - taking in the high cost of sustainable hydrogen - it starts to push the opportunity for hydrogen trains further and further and further towards the fringes of the network.