Power Grids

I understand that power supplied in any grid should match load demands.
How is this done in large grids supplied by coal/oil/hydro/nuclear/wind/solar/etc power stations, when the power demand varies unpredictably?
Is it real-time monitoring of power demand or is a constant maximum power supplied at all times with unused power going into storage?

Thanks in advance.

Ever thought of searching Wikipedia?
https://en.wikipedia.org/wiki/National_Grid
https://en.wikipedia.org/wiki/Electric_power_transmission

The point is that the grid provides voltage, not power as such. The power is determined by the load. It's like a battery. The battery just sits there with it's power (energy) not going anyway until you add a load. A generator can be running and providing a voltage but if there's no load, there's no power being used or generated.

As the load on the grid increases, then the power stations sense that the generators are being loaded more and crank up the power driving the genrator: more coal to the boiler, reactor power increased, more water through the turbines, etc.

thanks

Thanks all!