I'm not actually sure that that would be the major problem. A heat pump is basically a motor, which can cause a lot of noise in electrical circuits. I'm not sure you would want 1000s of electric motors turning on in unison. I wouldn't like to say whether that is a solved/solvable problem though.
The grid has a lot of inertia and a motor can go from full load to none, or from no load to extra-high startup load, in a fraction of a second.
So we're back to "just as fast" for this use case.
Where does the inertia come from? I understood inertia in the grid to come from turbines and motors spinning up and down, which seems to be different from what you're suggesting?
Capacitance in the wires?
With something like a heat pump compressor, you're connecting or disconnecting it completely with the flip of a switch. It's also an asynchronous motor and unable to feed power back into the grid at all, it's a pure load.
To put it another way. Say if energy use jumps X%, inertia may make up Y% difference in the short term, you'd still have to put in more than X% in the slightly less short term, and it would take longer to make up the Y% shortfall. Is the Y% shortfall not big enough to be important here.
If you add more load, you start dragging down the frequency. The more inertia you have in the turbines, the less the frequency is impacted. I'm not sure what you mean by "spinning up a turbine" in this situation. Do you mean to produce more power? You don't spin turbines faster to do that.
> To put it another way. Say if energy use jumps X%, inertia may make up Y% difference in the short term, you'd still have to put in more than X% in the slightly less short term, and it would take longer to make up the Y% shortfall. Is the Y% shortfall not big enough to be important here.
Yes, you have to make up the deficit. But the alternative means having a brownout. In a choice between "drain some inertia to cover the increased load, then overproduce by .1% to refill the inertia" and "don't cover the increased load, voltage freefalls until load drops", I prefer the former.
Reading around, as the amount of renewables (solar) increases this might become an issue due to less turbines being in use.
"spinning up a turbine"
As in spinning up to speed. It can't go 0 to X000 rpm instantaneously. Inertia!
Didn't realise they were designed to spin at a constant speed though, thanks.
Solar is trickier but it's also more flexible in how it injects power. The real issue is not lack of inertia but the fact that it can lose production when a cloud comes by.