Interesting question. I used to try to find the perpetual motion notion in these setups, but am still looking. Still waiting for the motherload to be delivered. . .
For the hydro based pumped storage, the "excess" power is stored as water that isn't allowed to go through the generators, i.e., the water is left in the upper lake.
Here. Think of this in component parts. The Load (all the homes and businesses), the Generator (just the generator), the Turning Thingee (the thing that spins the generator) and the Energy Supply used to make the Turning Thingee turn.
The goal of the PoCo is to keep any one Generator spinning at exactly
the same RPM all the time so that the 60 HZ frequency of the generated electricity stays rock steady. Valves or carburetors regulate the amount of the Energy Supply used at any instant in time to power the Turning Thingee to exactly match the turning push needed by the Generator to keep its RPM steady.
The thing that's easy to forget with macro
generators is that they act just like the little one at the construction site. When I turn on my drill, the generator loads down the motor and the carb governor gooses the motor and the generator stabilizes on the correct RPM. -- At home (on the grid) when I turn on the light, the same thing happens. . .it's just that the generator is so huge that its large inertia makes my light's load seem like it has no effect. But turning on my light does
slow the macro generator, and, if the RPM governor controlling the valve or carb is good enough, it will adjust the amount from the Energy Supply just enough so the Turning Thingee will keep the Generator rock steady at 60 HZ.
Any Generator has a maximum output beyond which it will hurt itself, same with the Turning Thingee. So the valve or carb only let in Energy Supply up to "the Max" and no more. Don't want to break the machine.
Lots of energy is lost, wasted, before going out of the Generator as electricity. The small construction genset loses are representative of the Macro. . .the exhaust gas heat, bearing and piston frictions, incomplete combustion, generator bearing friction, windage, hysteresis of the core and impedance in the wires. Normal generation efficiencies at the PoCo level are 20% electricity, 80% waste. There are schemes like using waste heat for the community that improve the efficiency some.
Last, the size of the construction genset is like the Macro. If I use a large 5 KW tool just a few times a year and the rest of the year I use small tools that together total to 2 KW and I buy the generator for the large 5 KW load, then most of the year I waste the ability of the generator while I wear out the Turning Thingee (the engine). As you suggest, Virgil, charging batteries stores energy and is kind of like the Pumped Storage. The motors that pump the water uphill introduce an additional loss of energy, but the cost of pumping verses the cost of running a powerplant big enough to handle the peak demand makes the pumping economically worth while.