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Comment by _whiteCaps_ | Hacker News Reader

> This is the first time a project of this kind will be used anywhere in the world and ESO believes it could be a “huge step forward” in running a zero-carbon electricity grid.

I'm trying to find some stats on this, because flywheel UPS aren't a new idea:

https://www.finning.com/en_IE/products/new/power-systems/ele...

https://en.wikipedia.org/wiki/Flywheel_storage_power_system#...

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What is different in this case is it is not really an energy storage system (at least that is not the main intended purpose), but only to provide stability to the grid frequency. A huge flywheel in a vacuum to provide a reference to millions of distributed PLLs. I don't think the idea is to always have it spin at a fixed rate with minimal losses.

In the case where a flywheel is used as a UPS, the rate at which it is spinning will vary in accordance with the stored energy.

You can get constant spin rate but variable energy storage / release by adjusting the moment of inertia, e.g. if you have movable weights within the rotor you can move these inboard or outboard, moving it inboard uses energy while increasing the spin rate, and moving it outboard releases energy while slowing the rate. Using this in combination with "conventional" direct axle energy input / release means you can store or release energy from the system as a whole while also keeping a constant rate (within the bounds of the total energy storage capacity of the system).

Is this used in practice? It sounds like a rather substantial engineering challenging considering how much energy the wheel is storing. I remember MIT had one of these for sparking the old tokomak, they had to plan for it to fall off, destroy several buildings without killing anyone, and then land in the river... and that was a solid wheel that did nothing but spin.

But isn't the point that it provides inertia towards stabilizing the frequency? I don't think it matters whether you can vary the energy stored if it's just acting as a, well, wheel... if the goal is to give you a bit more time to bring more generation online or take it offline then it seems like a simple system would be fine. It's not storing power, so it can only ever slow the drift to give more flexibility.

As you say, I suspect it probably isn't used much in grid scale applications. The device image in the article would imply that it is just a simple damper, i.e. the angular momentum acts to reduce any frequency change, up or down. It doesn't look like it does any storage, but then the article is somewhat content free.

What you are describing is essentially a centrifugal governor: https://en.wikipedia.org/wiki/Centrifugal_governor, I think?

You've seen what your washing machine does when you get a blanket off-balance in it.

Imagine if one of the motors on the flywheel stopped responding to inputs.

Windmills had governors which were horizontal wheels with two or more pendulums attached to the outer edge. The angular velocity is trying to lift the pendulum and gravity is pushing it back down, so velocity increases much slower than momentum.

The only problem you need to worry about there is seized bearings or foreign bodies unbalancing the load.

There are other devices that replace gravity with springs. You might be able to do the same with permanent magnets. But I believe each of these relies on the device being able to put up with larger strains than the pendulum.

It's kind of off topic, but your description reminded me of the executioner's sword "Terminus Est" from the Book of the New Sun series. It had a liquid metal (mercury I think) core that would collect at the base when held upright, making it easy to hold. When it was swung, the liquid would flow to the tip, putting more weight at the point of contact.

The point here is that the flywheel is so massive that the amount of energy required to bring it below (or above) the allowable frequency range is practically very large.

Large steam/gas turbines running on the grid have a similar effect. Even without hot gas running through them, they can provide rotational inertia for grid stabilization purposes. This flywheel is basically an extremely heavy version of the same idea, and powered exclusively by the grid itself.

You wont be able to ride out a scenario where there is a long-term lack of generation capacity, but this flywheel could buy the precious seconds/minutes required to spin up peaker plants and other contingencies.

How much mass are we talking about here? I'm curious and the article doesn't give any numbers. Order of magnitude at least?

No clue - I was hoping for numbers myself.

I'm curious about this is well. I imagine it must be huge to handle the scale of the grid!

Rotational energy goes up worth both the square or the radius and the speed, so it is much better bang for your buck to have a the mass centered on an outer rim connected to a hub by spokes and spinning really fast rather than just something uniformly heavy. The mass close to the centre doesn’t do anything for you.

The heavier it is also requires bigger more expensive bearings and accompanying system to get the thing spinning in the first place.

I looked at a flywheel that spun at 12,000 rpm. It was going to be located in an underground vault in case it ever got off its pedestal bearings it wouldn’t mow people down.

Like anything that stores energy but doesn’t generate the economics aren’t great.

> A flywheel-battery hybrid storage system has been installed in Ireland, a system that the companies involved claim is the first of its kind.

From 2016. Apparently part of the charm of flywheel storage systems is that they're always the first of their kind :)

(I suppose you could argue that the Irish one was the first with batteries and this is the first without, but really I suspect neither are either)

Here's what I was able to dig up, hopefully someone will be able to take this and run with it:

* nothing obvious at https://www.nationalgrideso.com/news * minutes from a 2011 meeting suggest that ESO was talking to Beacon Power at the time: https://www.nationalgrideso.com/sites/eso/files/documents/18... * http://credenceturbine.com/business/flywheel-energy-storage-... mentions Beacon Power providing a frequency regulation flywheel in 2014 for a 20 MW plant * "Techno-Economic Assessment of Energy Storage Technologies for Inertia Response and Frequency Support from Wind Farms" 2020 July 02, https://www.mdpi.com/1996-1073/13/13/3421/pdf discusses some details

This company is quite advanced, but now focusing more on research and IP:

http://afstrinity.com/company/

I've seen a system meant for hospital ride-through that packed an amazing amount of power into a relatively small enclosure using carbon fiber wound flywheels. For short durations you can get away with this because you're only going to operate one of those. Larger installations would need multiple of those and then you need to get very serious about containment so that if one of the flywheels ever fails it doesn't set off a chain reaction.

The nice thing about the fiber would units is that when they break they self destruct completely within the enclosure. The fiber acts as energy sink by breaking up, as opposed to a steel wheel that will spit out sizeable chunks across fairly larger distances (many meters).

Another player in that market:

https://vyconenergy.com/products/ups/vdc-products/

Grid stabilization is better done using superconductors rather than with flywheels.

I remember back in the early 2000’s my father was investing in a company building a flywheel. They were working on installing one in New York, not really sure what happened but I believe they installed one or two before the company went bust.

I remember standing next to a washing-machine-sized one of these in the server room at a local factory.

Yeah, I remember going to work with my dad (~20 years ago) at a datacenter for a large national bank. Power to the building was supplied by three large flywheels, which were in turn (usually) kept spinning by electric motors driven by street power. If they lost outside power, they had three diesel engines that they could spin up and clutch in before the flywheels spun down too far.

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