Reacción a "Massive power outage on the Iberian peninsula leaves millions without power supply"

How do you explain that something like this has happened?

‘Until all the information about the event is available, it is not possible to determine the cause of the event in a definite way, although it is possible to guess some of the reasons why it happened. The European transmission network operates with the N-1 safety criterion, which means that the system can continue to operate safely even if a network element fails. This means that the cause is not due to a single failure, but to a concatenation of events that led to the blackout. REE has indicated that the cause was a severe frequency oscillation, which occurs when the balance between the energy entering the system (that produced by the generators) and that leaving the system (that which is consumed, plus losses) is lost. This oscillation (whose causes have not yet been clarified), at a time when demand was low, photovoltaic generation exceeded 55% and there was a reduced contribution from generators that could provide inertia to the system (only 3% from combined cycles and 10% from hydro, with nuclear at half gas), meant that the system could not cope with the frequency variation and a chain disconnection of generators was triggered which, in the end, caused the blackout’.

Was it unlikely to happen?

‘The probability of this type of event is low, but it is possible that it could happen. In fact, the system operator (REE) has a protocol, which has been activated for the restoration of the electricity system after ablackout. However, REE has a simulator at the Tres Cantos control centre where operators are trained to resolve this type of situation, and others, should they occur. Thanks to this, service has been restored in a relatively short period of time despite the seriousness of the situation’.

Why did this happen on the mainland, and is it a more vulnerable region in Europe?

‘The peninsula has a limited interconnection with the rest of the European electricity system through France (just 4 GW), which puts it in a weak position compared to other more interconnected electricity systems. In addition, the fact that photovoltaic production is so high at certain times means that the system's inertia (rolling generation) and reactive energy management capacity to cope with frequency and voltage fluctuations is lower, which reduces its capacity to react’.

Could this happen again in the next few days and in the medium term?

‘It is not foreseeable that it will happen in the next few days, as I understand that the system operator is acting accordingly (today, for example, photovoltaic generation is half of what it was yesterday, although we do not know if this is because they have limited it for this reason or for other reasons), but it is an event that could happen again in the medium term if measures are not taken to prevent the conditions that produced the blackout from recurring. This will require a detailed analysis of the causes and action to be taken accordingly.

What needs to change so that it doesn't happen again?

‘In the short term, it would probably be necessary to limit photovoltaic production (which is already being done by REE's renewable control centre) to lower thresholds in periods of low demand, in order to increase rolling generation that provides inertia to the system to cope with frequency variations. In the medium term, the solution would probably involve strengthening the interconnection with France (and thus with the rest of the European electricity system) and installing frequency and voltage stabilisers in the transmission grid to compensate for the loss of inertia in the system due to the high penetration of renewables (especially photovoltaic). Another measure would be to improve the sectorisation capacity of the transmission grid to isolate faults and prevent them from affecting other areas, although this point is not obvious given the rapid propagation of this type of event. However, the rapid action of the protections in the interconnection with France is what has prevented the rest of the European electricity system from suffering the same effects as we have had on the peninsula’.