For all those desperate for another fix of facts and numbers, there's some in
a long railengineer article dated October 2020 and
a US presentation from April 2019. So these data can be added to the knowns list:
The
DC▸ bus voltage is 750 V, as it was before conversion. It's a very hard thing to alter, even if they have changed pretty much everything that connects to it, and of course it's essential to allow the option of third rail power.
The one thing I can't source explicitly is whether the new batteries are around 100 kWh capacity, like the initial ones. I think they are; I just can't work out where I saw that. But that's not all used; they are operated between 20% and 80% charge by agreement with Hoppecke. The bottom 20% is "get you home" reserve, but how can the top 20% be used as a reserve? My guess is that as they get older the upper limit of charge is allowed to go up to keep the same working range of 60 kWh.
The planned and/or guaranteed life of the batteries in service is seven years, after which they are either recycled by the makers at once, or used in a trackside buffer store for ten years first.
The fast charging is done per vehicle, and for this train that's two batteries each end. It has room for three, and for COP26 the third one was said to be "for resilience". Given the nature of that one-off deployment away from its home depot, this makes most sense if it was a spare that could be swapped in in any siding by moving a few cables or borrowing a forklift.
Exactly how many batteries are attached could have been altered, and indeed it could still change. There is room for three under each motor vehicle, and five under the central trailer. It may well be that the arrangements for using all of those, and for fast charging them, don't exist yet.
These new batteries need built-in cooling to cope with the "in excess of 1000 A" charging current per battery. So each fast charger needs to supply nearly 2 MW. I think that's within the range of what third rails and shoes can manage, though they do say they are using ceramic carbon shoes. Being static on the rail for several minutes may make the heat build-up worse, perhaps.
The objective to "fully replenish" a battery in 10 minutes, taken literally, but for 120 kW working capacity, requires 720 kW (a little under 1000 A). That has to be doubled for the vehicle. Balancing does waste charging current, and liberate heat, but it would be surprising if it added 10% to the charge current. But the numbers do match, more or less. Note that charging a battery needs a higher voltage, but the extra power isn't recoverable, so without extra information the numbers may not mean exactly what you think.
The US presentation includes a figure of 2 kWh per vehicle mile, which is a lot less than 9 kWh per km for three vehicles (nearly 5 kWh per vehicle mile). I wonder which is right? Either way, an 8 km round trip to Greenford would not take 10 minutes to replace. That's just as well, since keeping the current 2 tph with one train (as suggested by
GWR▸ ) only allow 6 minutes total for both ends.
If the highest figures apply, and it used 80 kWh per round trip, it needs to put back 20 kWh per battery. In two minutes that needs 600 kW - which can be done, according to the data above.
