> A heat pump (a compressor and some fans) can be switched on or off just as fast as a heating element,
This is not true, and the article specifically addresses this. A heating element can be switched on and off roughly five orders of magnitude faster (100 000× faster) than a heat pump.
This is not really an issue. Usually you have 4-5 seconds to react for the "hot reserve". Also for the known peaks you can preventively switch off the loads (it is amazing what happens at 7:02am when everybody switches on their kettle at the same time, even worse with water supply and flushing peaks).
In addition such systems sometimes measure frequency deviation and switch off/on the load when it goes out of bounds.
The result is that this works really well for fast balancing as soon as you have few hundred installed spots in one grid. And there is real money in it with ROI 1..3 years for the service provider.
Disclaimer: my electronics engineering company has worked with research, design and engineering of such load balancing hardware
You clipped out the qualifying phrase, “as far as the article is concerned”, dumping a few extra MW of electricity for 30 mins or a few hours. I don’t see a need presented in the article to rapidly switch a heating element on and off a few 1000 times a second.
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.
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?
The inertia largely comes from all the turbines and synchronous motors that stay connected.
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.
Ok I don't understand how that kind of inertia would help in this situation.
If a turbine is running, and supply and demand are at equilibrium, if you then added another load, that inertia wouldn't help maintain equilibrium, it would slow down spinning up the turbine hampering that goal, wouldn't it?
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.
> Ok I don't understand how that kind of inertia would help in this situation. If a turbine is running, and supply and demand are at equilibrium, if you then added another load, that inertia wouldn't help maintain equilibrium, it would slow down spinning up the turbine hampering that goal, wouldn't it?
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.
When you bring a new turbine online you get it up to speed before connecting it, and you can do this long before it's actually needed. So inertia hurts your response rate slightly but the main factor is how fast you can get your boiler or water pipe ramped up. That's why you see gas turbines as good peaker plants, they have very little to ramp up.
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.
You don't need it to switch on and off 1000s of times a second (is that what you're referring to?) you need it to switch fast enough that it could do that though. If it takes too long you would get brown outs and surges.
Maximum switching resolution is about 10ms in Europe (50Hz) and 8ms in the states (60Hz). As you usually switch at the zero crossing. In real life it is usually two-three orders of magnitude longer due to calculation and communicaton overhead.
I'm not an expert, but I'd think letting external factors control the switching on/off of your heat pump would have two downsides: (1) efficiency, and (2) wear and tear.
If you're talking about a heat pump used in air conditioning, at least, longer cycle times result in better dehumidification and higher efficiency. If you interrupt the cycle, you're effectively short cycling.
This is not true, and the article specifically addresses this. A heating element can be switched on and off roughly five orders of magnitude faster (100 000× faster) than a heat pump.