Thread by @BurggrabenH

Here is my theory how the major incident - a so called blackout - occurred at 12:30 CET today in the power system of Spain & Portugal:

1/n

At the time of the incident, Spain and Portugal operated the grid at very high renewables share of about 66% - i.e solar (55%) and wind (11%; eolica)

2/n

While this isn’t unusual for Spain, it does mean that the grid operates with little inertia (resistance to change) during such time. The grid is therefore vulnerable to external effects…!

3/n

In contrast, nuclear and fossil fuel power plants provide large amounts of rotating mass, delivering vital inertia to the grid — essential for a strong and resilient electrical system. This is why some grid operators cap renewable penetration at 25–35%.

Here’s a comparison between a typical nuclear plant and a standard wind turbine:

5/n

It gets worse. Solar power generates direct current (DC), but the grid runs on alternating current (AC) — like trying to fit a square peg into a round hole. Solar must be converted first, and, as you might guess, it contributes virtually zero inertia to the grid.

6/n

Inertia isn’t reported in real time by operators but I fed ChatGPT 4.0 with the data at the time of the blackout and here is the preliminary result: the grid was extremely fragile (low resistance to change)!

7/n

Another unusual thing I noticed is the demand (or load) data development in the hours before the major incident. It went down (yellow line).

This could be another source of unplanned problems for the operator. REE perhaps had to export more power than planned. IDK.

8/n

Then came reports of a forest fire and temperature-driven oscillations that may have further strained the already limited cross-border capacity between Spain and France. Either way, when the system needed emergency support, there simply wasn’t enough export capacity available fast enough to stabilize the grid.

9/n Source: Various

Putting it all together with the help of ChatGPT - step-by-step:

1. Very low inertia
Spain & Portugal were operating with 65+% levels of solar generation (>55%) and wind. Synchronous inertia across the peninsula was therefore low and far below historical averages, making the system vulnerable.

2. High northbound power transfers
Due to hot weather in France and Italy and abundant cheap Iberian solar, transmission corridors from Spain northward were heavily loaded, operating close to their stability thresholds. This left little room to export sudden shocks.

3. Initiating fault
A disturbance occurred on a major 400kV transmission line (likely between Spain and France). Possible causes include wind-driven line galloping, a lightning flashover, a wildfire affecting infrastructure, or simple equipment failure. Critically, two circuits opened nearly simultaneously.

4. Inter-area oscillation
With low spinning mass (due to solar & wind dominance), frequency oscillations between Iberia and continental Europe became unstable instead of being dampened. The frequency separation between the two areas grew rapidly — reported divergences exceeded 200 mHz.

5. Wide-area separation
Automatic grid protections activated. Under-frequency relays triggered widespread generation and load tripping. Several synchronous condensers and smaller plants disconnected. The Iberian Peninsula effectively “islanded” itself electrically from the main European grid.

6. Collapse in parts of Spain
PV inverters (solar farms) disconnected quickly due to fast frequency changes, and further generators tripped off due to extreme rate-of-change-of-frequency (RoCoF). Large regions blacked out, requiring black-start operations to gradually restore power.

10/n

Please note that this remains a preliminary theory based on incomplete information.

Entso-e will have to establish a full report of this major incident in the coming weeks at which time we hopefully know more.

11/11 End/thx