Re: The Physics Behind the Spanish Blackout

Carlos E.R. <robin_listas@es.invalid> wrote:

On 2025-06-10 12:08, Liz Tuddenham wrote:

Carlos E.R. <robin_listas@es.invalid> wrote:
 
[...]

>
Solar and wind can be made to impose a gigantic inertia with
appropriate
electronics. You can fixate the output at 50Hz, locked no matter what.

>
Only if the surplus energy is available to supply the necessary current.

>
Not needed.
>

>
Why not?

>
Think about it. Inverters can be locked in frequency to any timing
source.

 
If the source (grid) starts to fall in frequency the inverter will
either have to keep in step with it or supply massive currents as the
phase difference between the inverter and the grid begins to increase.
If the inverter tries to stay on-frequency, the time will come when they
are 180-degrees out of step, then things will get far too exciting.

 
Sure, same as any rotating mass that tries to oppose the drift. The
thing is, inverters have more "inertia" than rotating masses with a
turbine of the same power, if so configured or programmed to do.
Aggregating all of them, that's a huge inertia, way larger than rotating
masses.
 
Say, program to oppose 1% the drift. Whatever. There are engineers that
can study and decide what to do.

I think that you ignore main aspect of inertia.  You have a power
deficit and you need to adjust grid to compensate for lack of
power.  Inertia means stored energy which can be deliverd at
cost of lowering frequency.  IIUC in grid with rotating generators
and with similar deficit like in Spain it is supposed to give you
grace period of about minute or maybe 2 minutes.  In this time
control may try to activate new sources or start controlled
dropping of loads.  Current reporting indicate that inertia
in Spain was enough for 20 seconds and that was too little for
orderly reaction.

Sure, inverters can try to keep fixed frequency, but then
instead of too low frequency problem you get too low voltage
problem.  IIUC low voltage could lead to shutdown of the grid
in a fraction of second.

I can only say, if the cause of the Gran Apagón is found eventually to
be the lack of inertia in wind and solar generators, it is just a matter
of reprogramming the inverters or replacing them. An engineering and
economics problem, not a political one.

You can try to improve control algorithms so that they cope
better with short term power deficit.  Given scale of deficit
and observed result there may be space for improvement there.
But logically, you need some fast reaction energy storage.
Or some instantly swichable generating capacity.  But running
PV sources (or other) at say 80% of their true power (so that
you can instantly increase their output) looks rather unattractive
compared to energy storage.  You can use rotating masses,
for example run traditinal generator powering it from the grid to
keep it moving (so it does not need a turbine) or grid scale
battery.  Fast reaction energy store give you time to
activate slower sources like hydro or fast start gas powered
generators.  Or to drop loads in controlled way.

The point is that if you have power deficit, then grid can not
work well.  And without energy storage you may lack time to
switch on extra generating power (assuming that it is available).
Instantly dropping loads may be possible, but if it is the
only short term balancing mechanizm, then effect on loads may
be nasty.

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                              Waldek Hebisch