Energy expert Arvi Hamburg told ERR that the blackout in Spain was probably caused by over-reliance on weather-dependent generation. In Estonia, back-up power sources should prevent a similar outage from occurring, though it is not impossible that something could happen to that too.

Hamburg stressed that the more dependent a country becomes on unmanaged capacity, the greater its need for reserves will become.

"In Spain, there is a lot of weather-dependent generation, especially solar.  Presumably it was a situation whereby the production levels simply did not match the consumption anymore – there was not enough sun or win," Hamburg said.

Hamburg suggested the slow start-up of frequency reserves or insufficient inertia to ensure frequency as other potential reasons behind the power outages in Spain and Portugal.

"This means the frequency dropped faster than the frequency automation control could respond. And then all the consumers start to drop out one after the other. If the generation doesn't guarantee consumption, and the generation can't be increased quickly, then consumers are simply switched off," he said, stressing that this was still only a hypothetical explanation behind the outage.

Asked how Estonia is protected against similar outages, Hamburg said: "I don't think it's so bad at the moment that we ought to be afraid. The thing we  (in Estonia – ed.) have to keep in mind is pretty clear – we have to keep as much frequency reserve ready as possible in case of a consumption blackout. If one form of aggregation fails, another kind of connection fails in Finland, Lithuania or Sweden, then we have to be able to cope by ourselves."

Hamburg noted that the Baltics are connected to continental Europe via the Lithuania-Poland link. "This is a rather weak link, especially as we do not have a very strong connection to this large system either. We have to be particularly vigilant that we can manage on our own. 'On our own' is, at best, the three Baltic states, at worst, Estonia by ourselves," he said.

Hamburg added that the likelihood of Estonia being left separate from Latvia and Lithuania is small, but cannot be ruled out entirely. "That's why we have this insularity, that Estonia has to be self-sufficient – to cover its own production and consumption."

Hamburg said that, in theory, the Baltics' consumption would be covered by reserve capacity in the event of a power outage, but acknowledged that something could also happen to the reserve capacity.

"Theoretically we have gas stations in Latvia, and in Lithuania, the Kruonis Pumped Storage Plant has a pretty decent capacity. In a normal situation, in the event of an outage of the kind that we have planned for, we know that the back-up capacity is there and will cover it. But, the other thing is, even with the same amount of reserve capacity, something could happen. There is some kind of Latvian or Lithuanian gas station but it could be the case that it doesn't come on when it's needed," Hamburg said.

"Let's say that in theory we have all the reserves and there is no reason to worry, but you always have to be overly secure and careful."

Hamburg added that the more the electricity system becomes dependent on weather, or non-controllable capacity, the greater the need for back-up capacity, which in turn creates a cost for the consumer.

"We have to pay for it. Nobody can build a gas-fueled power plant if it only sells a few hours a year, just when it is needed. It has to be operational for 8,760 hours, all the time," he said.

Hamburg stressed that in the electricity system, production must match consumption levels at all times.

However, it is difficult to predict consumption and production, as generation is increasingly dependent on the weather. "This means that we have to forecast the weather – wind speed and sunshine – very far in advance. Forecasting errors will also start to have more of an impact," Hamburg explained.

Elering: There are also non-weather-dependent means to ensure inertia protection

Märt Allika, head of Elering's Energy System Control Center, said that energy officials in Spain and Portugal have so far not identified the cause of the outage.

Asked whether a similar outage would be possible in Estonia, Allika said it is highly unlikely.

"Blackouts like this happen extremely rarely, and Estonia has not experienced an outage so far. It is very unlikely that a blackout will happen in Estonia, but as yesterday's events in Portugal and Spain show, it is not entirely out of the question."

Allika pointed out that Estonia has the appropriate protection systems in place to detect a potential emergency and deal with it proactively. "We are also planning the network in such a way, whereby switching off one or two elements should not cause these kinds of high impact events to occur in the power system. There is also the day-to-day operational planning. In other words, we are looking at what we allow into the system and what we don't, to ensure its reliable operation," he said.

"The probability that an event like that could happen is extremely small. It is certainly not zero, but we are all trying to make sure that it is as close to zero as possible," Allika said.

British news outlet The Telegraph suggested the Spanish power outage could have been caused by excessive weather-dependent generation, which does not create enough inertia in the power system.

"There are other means of generating inertia. To take the example of the Baltics – we have three synchronous compensators that provide us with sufficient inertia. This problem can be solved in another way," said Allika.

"With continental Europe, there are two AC lines between Lithuania and Poland. In order to make this situation more secure, two new additional lines have been planned. If we have four alternating current lines between Lithuania and Poland, this should be a sufficient number of interconnections to give us the certainty that we will be in the European frequency band," said Allika.

TalTech professor: Estonia currently has sufficient reserve capacity

Jako Kilter, professor of power systems at Tallinn University of Technology (TalTech), said there is currently no information regarding what may have caused the outage, so he did not want to speculate on it. However, Kilter did not rule out the possibility that the blackout could have been caused by over-dependence on the weather.

 "That could be one possibility. Certainly it's about keeping a balance in how we plan the system – a lot of generation, consumption. In terms of production – what kind of generation units we have running. Better information on the actual situation will be available shortly from the Spanish transmission network. But yes, if you get your planning very wrong, all sorts of things can happen," the professor explained.

Kilter said he hopes a blackout of this type will not happen in Estonia, but admitted that technically there is a chance.

"Inevitably, we have a system that is constantly in motion, we don't have a static system – all the time, the production changes and the consumption changes. We have to make sure that there are enough reserves. Doing all this is a very challenging task," Kilter said.

In Estonia, Kilter said, a similar blackout could be triggered by, for example, a major power plant going offline or power lines going down in a specific corridor. "If we plan and build the grid in a way whereby  we have back-up connections in place and also have sufficient generation capacity available at all times, the likelihood of that happening is very low," he said, adding that he believes Estonia currently has sufficient back-up capacity.

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