The Spanish grid collapse
Inertia and why we need it
Last week, we released our first article from Issue 19, on how the FDA secretly liberalized animal drugs.
Yesterday, a significant portion of Spain and Portugal’s electricity transmission system stopped working in the span of five seconds. Spain, Portugal, and parts of France and Belgium lost power, in what is likely to have been Europe’s largest ever blackout.
To be clear, we don’t know the immediate cause of the outage. The Spanish grid operator said that a sudden outage caused the grid interconnection between France and Spain to trip. This resulted in the two countries’ energy systems disconnecting momentarily, triggering a sudden change in frequency.
Before tens of millions of people lost access to power, it appears that frequency across the Spanish grid dropped by about 0.15 hertz. Electricity grids rely on alternating current, which is current that regularly changes direction, switching back and forth in a regular pattern. Frequency is the rate at which this current oscillates. It is typically measured in cycles per second, or hertz.
Every country in the world has a grid designed around the large rotating generators used in nuclear, coal, and gas power plants. They rely on heat boiling water into steam to drive spinning turbines. These generators usually weigh over 100 tonnes and spin at over 3,000 revolutions per minute, meaning that they contain significant kinetic energy, like a very heavy spinning top. If supply drops, the rotor will begin to decelerate, but some of its momentum will be converted into electrical energy. This ‘inertia’ will buy the grid the few seconds it needs to activate its fast-response systems – deploying energy from battery storage and firing up small gas powered engines. This means that frequency should not fluctuate outside a small band even when a large generator trips.
Solar panels, on the other hand, directly convert sunlight into electricity without the use of rotating turbines. They are then connected to the grid using electronic inverters, which convert the direct current electricity generated by solar panels into the alternating current that buildings and the grid can use. These inverters don’t provide inertia. Instead, they either follow a pre-programmed frequency or mirror the rest of the grid. When the proportion of inverter-based resources versus traditional generators increases, the total physical mass spinning in the system decreases. This means there is less physical momentum to absorb any shocks to the system.
Maintaining a stable frequency is critical. Both the generators that power the grid and the devices that draw from it are designed to operate at specific frequencies. Many devices connected to the grid will overheat, experience mechanical stress, or break if the frequency of the current they receive varies. This affects everything from electric clocks to industrial motors.
The events in Spain and Portugal look like the nightmare scenario for any grid operator: a cascading failure. This is where an uncorrected frequency deviation causes a small number of generator trips, worsening frequency problems, in turn causing more generators to cut out. Much of Europe’s energy system is interconnected, which is how problems with Spain’s grid caused temporary outages in Belgium.
Restoring power after a system-wide outage like this is a painstaking process. A ‘black start’ involves using a blend of gas-powered engines, hydro pumps and battery storage to restart generation capacity. These islands of power are gradually connected to revive the main transmission network.
To avoid this slow process, the grid has a series of emergency mechanisms. In the UK, if frequency moves out of the 49.8 to 50.2 hertz band, it will begin shutting off power to parts of the system to restore balance to prevent any issues from spreading. As we are seeing in Britain today, renewables are posing a challenge from a grid management standpoint.
The European Network of Transmission System Operators warned at the start of this year that:
‘Reduced system inertia is a natural consequence of the lower number of directly connected rotating masses of synchronous generators to the grid. The stability support traditionally granted by these generators … will no longer be available in an almost exclusively RES-dominated [renewable energy source] system. This will expose the electricity system to the risk of being unable to withstand out-of-range events like system splits that were previously manageable.’
The inverter industry has been working to correct this, for example, through the use of grid-forming inverters. These use sophisticated control algorithms to set local voltage and frequency, emulating a synchronous machine. To make this work, the inverter needs access to some form of rapidly deployable energy, for example batteries. While this technology will likely one day become the norm, commercial adoption is still in its early stages.
Another option is to use a synchronous condenser. This is a rotating machine that spins freely, powered by excess energy from the grid, in turn providing inertia. One such facility already exists in the UK. For a cost of £25 million, it provides one percent of the UK’s minimum inertia requirement, suggesting that scaling this up could cost in excess of £2 billion – but £2 billion that would be well worth it if it prevented fires like the one that closed Heathrow from turning into catastrophic grid-wide collapses. Some forecasts suggest yesterday’s outage may on its own cut Spanish economic output by 0.5 percent this year.
Spain’s grid is powered significantly by intermittent energy sources. Shortly before the blackout, thanks to high levels of sunshine, 65 percent of generation was supplied by solar and 12 percent by wind. Nuclear supplied 11.5 percent and gas-fired generation 3.5 percent. In 2019, Spain committed to decommissioning its seven remaining nuclear reactors, although the government recently signalled that it might be open to reconsidering.
While the use of intermittent energy sources doesn’t cause power outages, lack of inertia makes it easier for them to spread. As Western countries continue to go full steam ahead on building out wind and solar capacity, policymakers are yet to face-up to these trade-offs or their financially painful mitigations. There’s also a more worrying question. Inertia may buy the grid one or two seconds to deploy energy it has stored in batteries or to fire up some gas-powered engines. But without spare large generation capacity, you will still expect to see blackouts. Most countries have built up enough fossil fuel reserves and battery storage to tide them over so far, but if an interconnector were to break at a high demand, low wind moment, all bets are off.
Alex is an editor at Works in Progress, focused on AI and energy. He’s also the author of Chalmermagne, a Substack covering technology, policy, and finance.