Because the general consensus seems to be that large things like pumped hydro are good for centralized energy storage, while batteries are the choice for decentralized energy storage -- whether in your utility closet or in your EV.
Why should anyone choose a flywheel over a battery?
Advantages over chemical batteries:
>85% round trip efficiency (DC)
>No daily cycling limitations
>No degradation over time
>Full power over full State-of-Charge range
>No HVAC required
>Operates in hot and cold environments (-20C to 50C)
>Fast response time (<1 second)
>Sustainable and recyclable all-steel design
>Safe & reliable–no fire hazard
>Lower O&M cost
>30-year design life
None of these are exactly a problem, they just cost money to implement properly.
I would say this copy + pasted list is not great.
No HVAC required - ok but you do need to suck down a huge vacuum, which is a lot more difficult than traditional HVAC
Hot and cold - see above point
All steel - not sure about that, maybe for lower speed applications, which reduces the amount of energy stored
Safe & reliable - hard to say that a huge mass spinning >100k rpm is "safe". By itself there is no fire hazard sure. but what if your magnetic bearings fail and it hops off and starts trying to escape it's (vacuum) enclosure. Then you have tons of sparks and pressure differences and other non-fun things.
O&M - [citation required]
30 year life - surely with all the plusses listed, it should be longer than 30 year life?
1. Pumped hydro is currently best for long term-storage. The lack of other cost-competitive long-term storage options is currently one of the biggest issues with renewables and an active area of investigation.
2. Batteries are good for daily smoothing (i.e. when the sun goes down), but they have limited charge/discharge cycles, they lose charge over time, and they don't, as of yet, have storage capacities needed for long term storage.
3. As the article points out, flywheels are good at instantly changing output based on changes in the grid, so they're good for frequency regulation and onboarding/offboarding new energy sources. Their biggest downside is their limited capacity compared to other tech.