certain electric loco builders/ operators are pretty proud of how much energy their regen braking captures, reducing the use of friction braking to virtually zero.
This is always under ideal conditions. Transformer and inductive device (e.g AC motors) highest efficiency occurs at a certain load point, and so manufacturers will state that as their claim (IC engines, for instance, at certain revs and intake pressure, often without accessory loads counted, like A/C, pumps and alternators). Under certain conditions, like regional service, locos (and EMUs) will display an ideal recovery of about 30% from braking, but of course, that's relative to the amount of energy used to achieve that speed (kinetic inertia) in the first place. Long distance, that ratio will sink, ditto short distance due to losses overwhelming the recovery gain.
Make no mistake, regenerative recovery makes a lot of sense, especially since it's so easily attained with modern control systems, but let me restate the point in this context: Catenary v. Hydrail, by the simple theory I understand at this point, catenary will recover slightly more due to the much lower source impedance. Think of it as a much larger flywheel, and suddenly you apply a negative (regenerative) force to it. The greater the moment mass of the flywheel, the lower the source impedance, and thus the greater the breaking effort/regenerative capture.
Another analogy: A large engine in a car on the highway v. a smaller one. All other things equal, not only do you get greater acceleration, you get greater deceleration when you take your foot off of the accelerator with the larger engine. With the smaller engine, the mass of the vehicle is far more prone to 'freewheel' the engine since resistance is so much less.
The way to make a Hydrail unit act more like a catenary source is to add more battery. But then you lose thrust to mass ratio even more. One of the huge advantages for off-vehicle power source for catenary locos is that thrust to weight ratio. It's unmatched by any other practical means at this time, save for perhaps linear induction, but has a host of problems too, and isn't inside the sphere of this discussion.
Hydrail has its uses, doubtless, but not for GO RER. Beyond the catenary network, yes, but even there sourcing the hydrogen is still highly problematic. In Germany's case, it's far easier, as it's part of a much larger federal program to supply H as an alternative fuel.
That does not exist in Canada, or many other nations. It's peculiar to Germany for reasons I'll reference if challenged. That's a massive point you touch on, and one that the 'obfuscators' don't care to discuss, let alone mention.
Edit to Add: Since this aspect is extremely important in the discussion of Hydrail (and one the 'proponents' are unlikely to discuss) I'll attempt to define 'source impedance' as that relates to battery storage v. catenary.
I've looked at various definitions, the easiest ones aren't entirely correct, the more correct ones are too technical for the layperson, and the point for this purpose gets lost.
The
output impedance of an
electrical network is the measure of the opposition to current flow (impedance), both static (
resistance) and dynamic (
reactance), into the load network being connected that is
internal to the electrical source. The output impedance is a measure of the source's propensity to drop in voltage when the load draws current. The source network being the portion of the network that transmits and the load network being the portion of the network that consumes.
Because of this the output impedance is sometimes referred to as the
source impedance or
internal impedance.
https://en.wikipedia.org/wiki/Output_impedance
This can be explained much more easily with an intuitive analogy, and a gear-box (or continually variable xmssn) into and out of a flywheel is one analogy that could do so. There's irony in that, as the early Routemaster buses tried this form of energy storage, and they came up against the 'energy density' problem: Propensity for catastrophic failure of the storage device. In the case of the Routemasters, the flywheels would de-laminate in an explosion that destroyed the bus. We're seeing this now with Lithium-Ion batteries, albeit a chemical reaction, not mechanical.
I'll see what I can find on-line later that puts the flywheel analogy in a more understandable way as per 'source impedance'. You've already touched on it with the tram analogy. At the risk of technically misstating this, "underpowered" will have to suffice for now.
Late Edit to Add: Wow! I went looking for the reference to the Sixties Routemaster mechanical flywheel experiments, and if you pardon the pun, that's come a full revolution since. I know Paul and a few others will find this very interesting, I suggest reading the entire article, this is another branch really of the Hydrail discussion, more comment on this later:
Urban legend: Hybrid bus technology
By
Kate Cummins 29th November 2010 12:00 am
[...]
flybus project in depth
The CVT/flywheel system offers an alternative to battery-based engines. The Flybus project began last year with the aim of demonstrating a viable alternative to battery-based hybrid buses. Earlier this month, construction of the first prototype vehicle began, which – according to project leaders – could deliver up to 20 per cent savings in energy consumption.
The project is headed by transmission company Torotrak, with contributions from Ricardo, Optare and Allison Transmissions. Research is based around Torotrak’s Continuously Variable Transmission (CVT) technology, together with a high-speed composite flywheel for an energy-storage system known as ’Kinergy’.
The team has used the high-speed flywheel, which recycles the kinetic energy that would otherwise be wasted in the brakes. As the bus slows, instead of converting its kinetic energy into heat in the brakes, the CVT transfers energy to the flywheel, spinning it up to speeds of around 60,000rpm.
When the vehicle pulls away from rest, the CVT returns energy from the flywheel to the bus, meaning there is less work for the engine to do and reducing fuel consumption. In the process, the flywheel gives up energy and slows down until re-energised during the next vehicle deceleration.
According to Torotrak’s engineering director, Roger Stone, the technology offers easier installation than battery-electric systems. It also provides comparable gains in fuel economy in a package that is half the size, half the weight and a quarter of the cost. [...]
https://www.theengineer.co.uk/issues/29-november-2010/urban-legend-hybrid-bus-technology/
Edit to further add:
Note reference to "Torotrak"above. That was seven years ago. Fast forward to this year, and due to being subscription only, I'll only quote a few paragraphs from the Financial Times:
Torotrak suffers as focus switches to electric cars
Traditional technology manufacturer loses out as groups invest in alternative energy
FEBRUARY 5, 2017
[...]
https://www.ft.com/content/456cc28e-e976-11e6-967b-c88452263daf
As indicative as this is for 'the electric route', it does not follow that Hydrail will do the same for catenary, *even if* it does for diesel.
