Why Restarting a Power Grid After Massive Collapse Is So Hard

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(Bloomberg) — It’s a worst case scenario that grid operators plan for but hope never to encounter. After one of the worst blackouts in Europe in more than a decade, electricity grid operators in Spain and Portugal are trying to get networks back up and running from the ground up. 

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The initial estimate from grid operator Red Electrica was that restoring all power supply in Spain may take between six and 10 hours. By Monday evening, that was looking optimistic — at 9pm Madrid time, there was 17.3 gigawatts of demand on the grid, about two thirds the amount seen just before the blackout happened, according to grid data. 

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It’s not clear what caused the initial disruption, or why it cascaded so dramatically into a widespread failure. But it’s notable that Spain has been one of the leaders in rolling out wind and solar generation, at a time when governments and grid operators across Europe are grappling with questions about resilience as renewable power takes an ever-larger share of the region’s energy mix. 

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Black Start 

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When there has been a failure on the entire grid, a complex process called a “black start” is needed to restore the network gradually. Smaller, often diesel, generators are used to start bigger ones, in a process that creates “islands” of power which connect together on the main transmission network to gradually restore the grid. 

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European rules require grids regularly test their black-start capability, so operators should have a clear plan to follow. But the process is painstaking and complicated.

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“These islands of power then need to be all synchronized together,” Simon Gallagher, managing director at UK Network Services, said in a post on LinkedIn. “Not simple and again, takes time and has to be very controlled.”

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Essential services like hospitals will have their own on-site back up generation, usually diesel engines and stores of fuel. Other commercial entities like data centers also pay to have emergency back up generators and batteries to secure supply. 

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Read: Data Centers and Mill From 1929 Have Better Backup Than Heathrow

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Frequency Factor 

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So far, the only information about what caused the crisis was a comment from grid operator Red Electrica that the blackout was a result of “oscillation,” which suggests a disruption in the grid’s frequency or voltage — both crucial factors for maintaining stability. The frequency, which normally stays pretty steady around 50 hertz, is the heartbeat of the grid.