Renewables like solar that can not be modulated are a PITA for grid safety as those plants that instead can, such as coal and gas, then need to scale for solar suddenly dumping energy into the grid.
Day-before markets exists for this sole reason.
It's through a smart inverter, of course it can be modulated.
Now, random consumer solar can't easily be modulated - yet. But nor can random consumer demand. If you've got a big solar farm then not only can you precisely control the output, you can also control the phase response of the output.
(if you turn the inverter off, what happens is the panel voltage floats up to the breakdown voltage of the photodiode that is the solar cell, and the energy vanishes into electron/hole recombination and slightly warmer panels)
You can easily disconnect solar plants from the grid - even remotely if the situation requires it (technically even gradually if it is supported by the specific plant). This is required by law in e.g. Germany: the higher the peak power the higher the requirements in flexibility generally speaking
> On–off keying (OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave.
https://en.m.wikipedia.org/wiki/On%E2%80%93off_keying
Idk how you define modulation. Note that on/off isn't a worldwide switch, but only one for tiny units with respect to the whole energy grid
The page you googled has nothing to do with how the power grid operates.
Non-dispatchable renewables like wind and solar can only be curtailed when their supply is not wanted.
Solar panel farms with advanced inverters in some markets actually make a significant portion of their revenue from the frequency control ancillary services, and Solar+storage is extremely dispatchable.
That is exactly what I meant, and renewables introduce uncertainty as the output can vary (think of a cloudy day).