Most flywheels in use are on gensets and only last a few seconds, keeping the generator spinning until the genset has ramped up to speed.
There are standalone flywheel systems but they're not nearly as common now that genset flywheels are around, in part because they have atrocious recovery time, they're far more complex and expensive (they tend to spin at significantly higher speeds, do so in a low-viscocity gas or vacuum, etc..and don't utilize a power unit that already exists) and they cannot help start a generator whose starter has failed.
Their main advantage, like you said, is that they don't degrade with age or use, but they're also compact and far less hazardous than large battery rooms.
Their major downside is that their recovery time is atrocious. There was a huge outage at an SF datacenter many years ago that was caused by multiple short outages. The flywheels didn't have time to spool back up between outages and eventually didn't have enough kinetic energy to carry things until the generators came back on.
Pumped hydro operates on a scale orders of magnitude larger than flywheels and batteries and has a response time of seconds, which is plenty sufficient for a grid-scale operator, because the grid has enormous inertia. It's the fastest responding form of large-scale power generation (natural gas takes minutes or more, nuclear takes days.)
One of its major successes has been in the UK, where for decades pumped hydro has helped the grid sustain "TV Pickup" - everyone flipping on their electric kettle between BBC programs.
Yeah, pumped hydro has response times on the order of 10s of seconds, but the capacity is only useful for short term generation. For example, the UK has 24 GWh of installed PHES capacity. Last year the UK used ~915 GWh per day on average, so best case about ~40 minutes worth of consumption.
PHES is for peaking and grid stability, not long term storage.
What is long term storage in the context of renewables? Scaling UKs PHES capacity times 40 so that it lasts a whole day doesnt seem like an impossible task. I might be naive, but it seems extremely possible, given how those 24 GWh capacity were achieved with little to no political support.
There are standalone flywheel systems but they're not nearly as common now that genset flywheels are around, in part because they have atrocious recovery time, they're far more complex and expensive (they tend to spin at significantly higher speeds, do so in a low-viscocity gas or vacuum, etc..and don't utilize a power unit that already exists) and they cannot help start a generator whose starter has failed.
Their main advantage, like you said, is that they don't degrade with age or use, but they're also compact and far less hazardous than large battery rooms.
Their major downside is that their recovery time is atrocious. There was a huge outage at an SF datacenter many years ago that was caused by multiple short outages. The flywheels didn't have time to spool back up between outages and eventually didn't have enough kinetic energy to carry things until the generators came back on.
Pumped hydro operates on a scale orders of magnitude larger than flywheels and batteries and has a response time of seconds, which is plenty sufficient for a grid-scale operator, because the grid has enormous inertia. It's the fastest responding form of large-scale power generation (natural gas takes minutes or more, nuclear takes days.)
One of its major successes has been in the UK, where for decades pumped hydro has helped the grid sustain "TV Pickup" - everyone flipping on their electric kettle between BBC programs.