It sounds likes you are describing synchronous condensers: https://en.wikipedia.org/wiki/Synchronous_condenser

Yes! Thank you. I had no idea they were called this. It was difficult to believe that something like this didnt already exist.

What you're describing is effectively a utility-scale flywheel, which at least one company is trying.

https://www.revterra.io/

I believe the idea is to shift to synthetic inertia, which like synthetic diamonds, can actually be better than the real thing, but people get weirdly sentimential about the flaws in the one they are used to.

The terminology seems to be somewhat in flux.

If an inverter based resource has the right software and control scheme setup, it can mimick either inertia or primary frequency reserve. Although I think they're generally calling it all FFR (fast frequency response) now anyway.

When a frequency event occurs, the rotating masses of conventional generation arrests the decline in frequency for a very short amount of time (this is caused by inertia), and then the control schemes of generators respond to assist with fully stopping the decline and some degree of recovery (PFR or primary frequency response). After that, your secondary reserves of (regulation) help take it back up and then (spinning reserves) until frequency is back at nominal.

So, yeah FFR can be better than the conventional approach of inertia + PFR. Everything has to be configured properly (not any different than conventional resources, except FFR is still pretty new).

Are we claiming there are zero downsides to synthetic inertia when compared with its real counterparts?

That appears to be the case in Australia’s NEM grid, where utility scale batteries are able to meet synthetic inertia needs [1] (as well as preliminary trials of grid forming inverters in Chile, which NREL took part in [2] [3]).

[1] https://www.energy-storage.news/news/australian-transmission... (Australian transmission operator’s commercial arm to tender for 300MW unsubsidised battery project)

[2] https://www.nrel.gov/news/features/2020/renewables-rescue-st... (Renewables Rescue Stability as the Grid Loses Spin)

[3] https://www.nrel.gov/docs/fy19osti/73207.pdf (NREL: Highly Accurate Method for Real-Time Active Power Reserve Estimation for Utility-Scale Photovoltaic Power Plants)

Also https://reneweconomy.com.au/inverters-are-solving-grid-issue... ("Inverters are solving grid issues at fraction of cost of spinning machines")

> The operators of four large scale solar farms in north Queensland have found that “tuning” their inverter settings has enabled them to solve “system strength” issues at a fraction of the cost of the current default mechanism – spinning machines.

> Ian Christmas, head of engineering at Edify Enegy, told a Clean Energy Council large scale solar forum last week that the inverter tuning at four key solar farms – Whitsunday, Daydream, Hayman, and Hamilton – would address recently declared system strength issues in that part of the grid at one twenty-fifth of the cost of installing a synchronous condenser.

> He also said it could be done in a fraction of the time – around four months compared to fourteen months or longer for the alternative. “It’s significant enough (in terms of price and time) that it is a no brainer,” Christmas said.

> That a cheaper solution has been found for system strength is significant, because it highlights how new technologies are proving that they can provide many of the services previously thought only possible through spinning machines, such as those used in coal, gas and hydro plants.

I’d assume the extra complexity would be a huge downside. If the control logic of the synthetic inertia can be disabled, it won’t work.

A heavy rotating mass will continue spinning no matter what until mechanical losses (or external forces) stop it.