Rick,
there's more to the show than certain interest groups would have the average punter believe.
In an AC system, every generator and synchronous motor is sitting in lock step with each other, and their mechanical inertia adds to the ability of the grid in total to to manage "stuff"...in theory, turning on your lights when you get home from work causes something somewhere to respond...load increases to the grid drop the frequency a little (power is torque*RPM, so dropping frequency immediately levels out the power...it's the signal back to the generator that it needs to load up)
Thermals, nukes, GTS, Hydros will respond to that via their governor response. Same as your mower, when the speed drops, the governor will open the throttle valves (thermal, Nuke, Hydro), and the electronic control systems will start to feed in more fuel.
conversely, when the load drops, e.g. by a smelter tripping, or a transmission line outage, the frequency immediately rises (same power spread over less load), and the governors will drop the power output to get it back to normal...again, the thermals, nukes, hydros and GTs will do that automatically, then their control systems will start backing off the fuel.
The grid will be connected to these machines and ask their control systems to ramp up or down as needed for their pricing, and position in the pricing (bid) structure.
The Solar/wind don't do any of this regulation...they harvest energy and pump it into the grid at whatever the source is providing at the time. They don't ramp up when the grid gets loaded, and they don't ramp down when load drops off.
As they become a bigger part of the system, they make the regulation of power flows fall onto a fewer number of machines capable of doing that control...
Other things are power factor correction, which the big machines can do by changing the excitation of the generator, or changing the local voltage (changing transformer tappings).
Again, the wind/solar don't provide that.
It can be done, Static VAR Compensators (VAR being Volts Amps Reactive, the square root of -1 part) involve capacitor banks that are switched in and out as needed.
There's been thermals converted into "synchronous condensers" where the turbine is cut off the generator, and the generator spins, controlling local volatage, frequency, and power factor.
Immediate frequency response can be done with batteries, but has to be backed by something that can hold the load up.
Problem is that the solar wind get to generate first, are bid at zero, and get whatever the thermals are getting for their load, but don't have to provide the system stability.
System stability is undervalued while all the old tech stuff can still provide it. But the systems are becoming less stable.
As the push for renewables continues, the stability part will (IMO) become the money maker rather than straight energy conversion...and people won't be happy paying more for the "imaginary" part of power delivery.
