The latest refurbishment of the existing battery locos retained lead acid cells - and not replaced by newer technology batteries was for two reasons AIUI - one was there is no need for lighter batteries in a battery loco you need weight for adheson and that may as well be the battery cells, the other was far far too many hoops to jump through (and pay to jump through) to safety approve and certify a different battery technology. You can be sure if not approving just an alternative battery type is so significant it becomes a problem, then approving anything else will still be more of a problem. I'll cite the Schoema diesel conversions to battery as an example of complexity and costs (and in this case not progressing) type approval is; it does not matter what the blocking point is (in Schoema case AIUI it is EMC) all safety approval is complex and costly.
Existing LU battery locos operate in a strict regime. They do not operate on running lines in traffic on battery, they only use battery within possessions with traction current off, or in the few non electrified yards (e.g. Ruislip). Nor do they charge off running lines, they only charge while static in depots (either off traction current rails or shore lines). All that is because of potential gas build up of - yes - hydrogen during charging. Not just H2 but O2 and in explosive mixtures. If the regime is such that thou shalt dare not give off H2 from an existing type, you can be pretty sure H2 as a fuel ain't going to go very far without significant costly work.
And. The valid point was made upthread about the L62-L67 never lasted due to complexity. Well, introducing anything more than battery-electric will introduce complexity.
And. Add the costs of re-fuellng plant which will need new handling equipment (for ALL fuels) and specialised handling equipment for anything exotic be it hydrogen or plutonium or compounds thereof or anything else. This all adds great costs to an enterprise that can't even afford new trains for it's core business - so engineers luxuries won't get a look in.
Mines locos are a red herring. LU is a fully electrified railway; thus it is logical for the auxiliary source to be directly compatible with an electric loco. ITYF any mines loco referenced here are for unelectrified mines railways, hence these always need a local power engine source.i.e. they seek an alternative to an internal combustion engine of some sort, not an alternative to battery, surely?
Anyway, I ask a variation on 130 in the post above, can anyone cite where actually are there series productrion hydrogen powered underground mines locos anywhere in GB, or anywhere else - which means exclude past tests and prototypes that are no longer in use. For GB I am struggling to think where there are even working underground mines locos anywhere, excluding preserved and tourist operations. and it is GB safety compliance that will have to be got through.
I suggest the only reason anything other than battery appears now, which is before ITT, before tender, is that is standard wording put out to cover everything and to be seen to be attempting to be green. Since batteries are 'green' anyway, a goodly number of boxes are already ticked.
I do not like to dismiss progress, and never move forwards, and ever cling to old technology - but in this case I'll make an exception, I just do not see how anything else is going to be practical - and more importantly economic - when you take into account the huge varying needs and limitations of this Victoria and Edwardian and 1930s tunnel infrastructure we have.
And, I'll end with adding there was a project about half a dozen or so years ago to go for engineers locos replacements - and they were exactly as suggested, battery + electric, and no more.
IMHO the replacements will be no more than battery electric as they are now, possibly a different battery type if it can be assured, or, possibly, a hybrid with a alt. fuel diesel engine for surface charging, which would be useful as they could then theoretically charge while away from Ruislip, but I have no idea if that is necessary anyway.
