[uticus]

> So, after all those television-watching Britons go to bed, Dinorwig’s generators are run backwards.

> It’s a remarkably efficient process, with about 75% of the energy available for reuse.

Not an (hardware) engineer, so wondering: are turbines typically efficient running both ways? Or would a turbine in this scenario have tradeoffs compared to turbines that are designed for running in one direction only?

The best I can come up with from the comfort of my armchair is that straight gears are typically equally efficient in either rotating direction, but often gears with angled teeth are used when one rotating direction is primary.

[adhesive_wombat]

The Dinorwig turbines are (like most hydro plants) Francis turbines. The blade still have an angle. Like a PC case fan, the angle is the same direction whether or not the turbine is "braking" or "pumping". But there very likely are tradeoffs in the turbine design to keep both functions relatively efficient.

There are also what are called ternary sets, which are the generator turbine, the torque converter (a massive clutch) and a pump. A good diagram in here: https://voith.com/corp-en/11_06_Broschuere-Pumped-storage_ei.... These are used at another Welsh pumped storage station: Ffestiniog.

Helical gears (the ones with angled teeth) are used not because one direction is better than the other, but because they have a larger contact area and allow larger forces for a given tooth size (module) and lower vibration because multiple teeth mesh at any time rather than one-by-one. The angle can go either way, and, indeed, can go both ways on one gear (a herringbone gear) to nullify the axial loading.

[bee_rider]

It couldn’t be much worse, right? Otherwise they’d have just installed another turbine facing in the other direction.

[uticus]

I have no idea.

I can easily imagine a turbine being a good chunk of the installation BOM cost and budget constraints saying price recoup in x years that extra parts doesn't balance against. And in this scenario, then no, another turbine facing the other direction would not be an option - though it is only efficient one way.

[bee_rider]

That’s fair.

You were clearly looking for an answer from somebody who knew something about the field, but I decided (for some reason) to come in with, like, over simplified first principles speculation. I hate it when people do what I did, haha. Sorry!