As another commenter says, it's actually easier the more generators you have because the rotational inertia of all the spinning masses is larger. This (and the storage problem) is one of the reasons that wind and solar destabalise grids - they are interfaced to the rest of the grid by converters that create ac sources - but there's no real rotating mass there, so the inertia is tiny. The result is that as we add more renewable power to the network, it becomes less able to 'roll with the punches' of loads coming on and off line.

PS One of the answers in the SO thread mentions JET in the UK. I spent a few summers there as an electrical engineering student (it's home to the MAST and JET fusion reactors). When the JET tokamak ignites a plasma, it can't sustain it for very long (we are not yet at the point of extracting enough energy to sustain the reaction). As a result they need to ignite the plasma and keep it hot. They can't do it for more than 1-10 seconds. During that time, they draw massive amounts of power - they're permitted to draw up to 1% of the UK's capacity for a short period, whilst they simultaneously dump all the energy stored in two gigantic flywheel generators housed in a nearby building. I've never been there when the flywheels are running but I've climbed around beneath them. There's nothing quite like massive engineering :)

> This (and the storage problem) is one of the reasons that wind and solar destabalise grids - they are interfaced to the rest of the grid by converters that create ac sources - but there's no real rotating mass there, so the inertia is tiny. The result is that as we add more renewable power to the network, it becomes less able to 'roll with the punches' of loads coming on and off line.

Other problem is that for renewables to be profitable you want to push all the energy out all the time, especially in peak. Even now solar installation users have problem with that when there is too many small solar installations installed on same street the voltage goes too high and the inverters just trip and stop pushing the power to the grid, losing owner money.

We just need to have more cheaper storage solutions. Technically utilities could just put a bunch of batteries near concentration of residential solar and just basically sell the service of "storing the kilowatts" to them (say "you can receive 80% of what you put into it in next 48 hours"), all while having the capacity to use that stored joules in case a peak needs to be handled

If the inertia of turbines helps cover small loads, couldn't that be scaled up with a bunch of flywheels connected to motor/generators? Seems like it would be better able to handle sudden changes in the network than batteries+inverters.

Yes - this is precisely what was trialled in the UK a few years ago. You can basically take old decommissioned generators and just take power to spin them up - thus, you've just (re)created rotational inertia on your grid. It's a bit absurd, but it does work!

It's not hard to keep it in phase. Once it's synchronized it is actually rather hard to not keep it in phase.

Generator spins at 50hz Motor spins at 50hz

Add load to the motor, it starts slowing down both itself and the generator. Generator governor increases input energy, frequency goes up. Both are in phase all the time.

Remove load, both start spinning faster. Reduce governor to regulate it to 50hz again.

It's a bit harder with inverters but the idea is similar, you follow the grid phase and if you want to send energy to the grid you will be slightly early to the grid phase and if you want to take energy from the grid your phase will slightly lag.

> Heh, it's easy to model when you have a few generators, especially when one is much bigger than the others on the grid. But what's fun these days is you can have an absolutely huge number of generators. Keeping things in phase just seems insane to me.

The difficulty is not "keeping them in phase", that just happens (aside from initial connection), it's the whole load prediction and handling, when to tell which plant to start producing more or less energy, with variety of plants having shorter or longer ramp-up/down periods

It's a bit like they are all connected together by gears. All the generators are in phase.

The most difficult bit for an operator is to make sure the generator is synchronized before they actually connect it. Only after it's synchronized can they start actually feeding power in.

You can't just turn these things on and off at will like a regular motor. To extend the gears analogy, gears need to be synchronised before they can engage - just like synchronous AC generators.

During the Texas blizzard power outages, the state was supposedly minutes away from a black start scenario[0]. Estimates are that it would have taken weeks to restore power to the state owing to the complexity of syncing everything back together.

[0] https://arstechnica.com/tech-policy/2021/05/texas-power-outa...

I was here in Austin during that power outage. A few days was horrible enough as it was. If it had been weeks, I think we would have died.