[PSUBS-MAILIST] Flywheel energy storage

[Antoine Delafargue via Personal_Submersibles]

Hello
As a venture capital investor in energy storage startups I have tracked
several startups in the field, many of which did not make it as lithium ion
batteries got cheaper.
There are still some active like Chakratec in Israel. But the targeted
applications have narrowed down to cases where high power vs energy
capacity (like ability to do a full discharge in less than 15mn) and where
tens of thousands of cycles are needed. This is not what subs need.
Otherwise it is just too expensive.
Over time i have been impressed by the amount of beautiful engineering that
has gone into these things, notably to make them spin faster (kinetic
energy scales with speed squared, whereas it is just proportional to
rotating mass), with carbon fiber rotors, frictionless magnetic bearings,
vacuum chamber and as Cliff said failure management.
Using them in a moving platform would not be good for bearings too.

Regards
Antoine





Le dim. 21 mars 2021 à 18:54, Cliff Redus via Personal_Submersibles <
personal_submersibles at psubs.org> a écrit :

> I really think there is merit to the concept of using a high speed
> flywheel system as a replacement for batteries and some of the ballast.
> Tim correctly points out issues associated with induced forces and moments
> on the boat if the flywheel is not gimbaled or if there are not two
> counterrotating flywheels.   I briefly looked into flywheels before I
> developed the R300.  One of the interesting issues is how you design for a
> potentially catastrophic failure where the flywheel comes apart.  Because
> there is so much kinetic energy that could be released over a fraction of a
> second if you had a flywheel come apart, a lot of advanced high speed
> flywheels are made with layered composites that are designed to delaminate
> slowly and turn into a big bundle of strands rather than come apart in
> pieces.  If you like, planned failure.   I ran across an interesting book
> on flywheels many years ago that discussed the optimum shape of a high
> speed flywheel.  They used a computer model to predict the perfect shape
> for maximizing kinetic energy storage  while holding the stress in the
> flywheel more or less constant  regardless of the radius.  It turns out the
> shape is no where near what a low speed flywheel looks like which has a lot
> of mass in the rim and a then web.  Advanced high speed flywheels are thick
> at the axis of rotation and get thinner as the radius increases.
>
> For for a flywheel to work, I think you would need to couple with a
> motor/generator that could be driven with a small IC engine when the boat
> is on the surface.
>
> Cliff
>
> On Sunday, March 21, 2021, 10:30:50 AM CDT, Sean T. Stevenson via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> I was just envelope sketching a concept design, and I was struck by a
> thought: would a sub design using flywheel energy storage instead of
> batteries be feasable? I guess it would depend on design mission duration,
> and how frequently one could reconnect to shore power to spin it up again,
> but it occurs to me that if you could achieve the necessary storage
> capacity (kWh), there are several advantages to mechanical energy storage
> over chemical in the submarine environment.
>
> Thoughts?
>
> Sean
>
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