Does the energy consumption model include the effects of wind speed ? That can have a significant effect on resistance to motion of a train, and it can get quite windy across the Pennines.
Also, almost all batteries have a finite number of times that they can be recharged, and many gradually lose capacity when they get old. Can this affect the economics of battery train operation?
The model is not that sophisticated, I also don't know whether wind was included in the original power usage specs I pinched. I presume that it isn't as I would assume that eventually it would all cancel out.
I have factored at least 10% remaining capacity which would give some margin for extra energy usage. Also in an out and back you'd probably get some benefit of reduced energy usage on the return. Finally you could just increase some of you dwell times to take on some more energy if bad weather is predicted.
Also an actual purpose built BEMU is likely to have less drag than a class 800 even if it's in a headwind.
The batteries I have assumed are LFP types which can take in the region of 5000-10,000 deep discharges. Though obviously not every trip will include a full discharge, either way you are looking at the battery lasting more than typical periods between major refurbishments. The battery is likely to cost in the region of £250k so it's no biggie if it needs to come out then, that equates to about £70 per day per train so even with finance costs it's not going to impinge on ticket costs.
The other key points are that this is a very dynamic area. With battery life you aren't fighting physics to improve it so there isn't hard limits on how long cells can last for. The energy storage market also means that there won't be a point at which cell life isn't worth increasing and designers will go focus something else.
Remember that if you're going to recover the kinetic energy of the train under normal braking, then the batteries will need to be able to accept charge at a rate equal to, or even higher than, the maximum rate of discharge used buring acceleration. This will be several Megawatts.
Stadler claim that their FLIRT Akku has a full recharge time of just 15 minutes under the wires.
I used to have a Tesla so yes I understand variable regen depending on charge!
My model isn't sophisticated enough to handle that at the moment. As I stated before I was using a class 800 as the basis of the model, the energy consumption figures for that were inclusive of regen braking.
As a ground up BEMU will probably do better from an energy efficiency perspective I am currently happy to assume that some loss of energy recovery will be acceptable when the battery is at high states of charge to deliver a similar range performance as in the model.
Does anyone have a typical deceleration profile for an approach to a station, I'll incorporate it in future runs?
My early figures indicate that once SOC get below ~60% multiple MW of regen are possible.
There are a few solutions I can think of to the issue. The technological ones are:
1: Fit a bigger battery rarely take it past 70% SOC.
2: Fit a super capacitor and use it to accelerate away from the station KERS (having done some maths on this current super capacitors have approx. 1/15th the capacity of an LFP battery, ergo they'd need to be 15 stops between charges to make this worth doing)
3: Bank on charge speeds increasing in general
Or none technically, adjust route timings, trade slower braking and/or longer dwell/charge times for faster acceleration. Have the schedules cognisant of SOC of BEMUs.
If we go full BEMU with 3-4x EMU power outputs then we'd be looking at getting minutes back on the schedule every time it pulls away from a station, which gets me back to the concept that I think eventually all intercity trains will end up being BEMU (or maybe have a super capacitor onboard) just for the extra performance without needing to vastly improve OHLE.
