At 12.33pm on the 28th of April, swathes of Spain and parts of Portugal were plunged into darkness: trains were stranded, phone and internet coverage faltered, and ATMs stopped working.

The electricity blackout across the Iberian Peninsula is believed to be one of the worst in Europe’s history.

While most power was restored by the next morning, weeks later the investigation into the blackout is ongoing.

Last week, Spain’s energy minister Sara Aagesen said so far it was clear an abrupt loss of power at a substation in Granada, followed by failures in Badajoz and Seville, led to a loss of 2.2 gigawatts of electricity, but that the precise cause was unknown.

In the wait for answers, some have pointed the finger at Spain’s high reliance on renewables and reignited debates over plans to phase out nuclear power by 2035.

Are renewables to blame?

Spain is one of the leaders in Europe’s green energy transition and has ambitious targets for renewables to provide 81% of its electricity by 2030. Last year they accounted for a record 56% of the country’s electricity and solar capacity grew at almost twice the European rate.

Shortly before the blackout, renewables accounted for around 70% of Spain’s electricity production, mostly from solar.

This has been used by members of the opposition party and nuclear advocates to suggest that overreliance on renewables was at fault — which both the country’s grid operator Red Electrica de Espana and prime minister Pedro Sanchez have disputed. Nuclear currently provides around 20% of the country’s electricity.

While solar and wind are dependent on weather, nuclear can provide a relatively continuous baseload power. However, Sanchez has said there is no evidence more nuclear capacity would have prevented April 28th’s events.

Using the event to speculate against solar is more politically motivated than factually-based, said Rutger Schlatmann, head of solar energy at Helmholtz Zentrum, an energy research center in Berlin.

Schlatmann points to the fact that the high percentage of renewables in the grid was nothing unique. “This has happened many times before.”

Earlier last month Spain managed to cover 100% of electricity demand on a weekday with renewables alone.

Schlatmann added that countries like Germany also have experienced a high percentage of electricity from renewables while remaining one of the most stable power systems in the world.

How to improve grid stability?

Experts suggest the Spanish blackout highlights grid stability issues more than problems with renewable energy sources.

“It’s mainly that the system has not adapted on the grid scale enough yet to the massive change towards these renewable sources,” said Schlatmann, adding many electricity grids still reflect the demands of a fossil fuel system.

The grid is often described as the most complex system ever devised by humans — encompassing an intricate network of generators, transmission and distribution lines that all need to be kept in balance to function.

Nuclear, coal and gas power plants have huge steel generators that provide large rotating mass — often referred to as inertia — that can maintain stability if there are fluctuations in the grid.

While removing these from our power grid changes the way a system behaves, it is now possible to replace their stabilizing function, explains Robert Pietzcker, senior scientist at the Potsdam Institute for Climate Impact Research.”You can do virtual inertia, like with these inverters that have grid forming capabilities.”

Inverters with grid forming capabilities help create a type of “synthetic inertia” and stabilize fluctuations in the electricity system. 

The technology to create synthetic inertia — which involves electrical storage and improved control systems — are already available on a commercial scale but aren’t yet implemented on a national or European scale, said Schlatmann.

Other solutions that can also provide stability are flywheels, with the largest in the world today built in Ireland. Flywheels use cylindrical rotors that accelerate at a high speed, storing kinetic energy that can be used quickly when needed.

Better battery storage and increasing flexibility in grid systems is important, said Stefan Thomas, head of energy, transport and climate policy at the Wuppertal Institute in Germany. “More connections to neighboring countries that can help to keep the system in synchronization around the 50 Hertz.” Maintaining a stable 50 Hertz frequency is essential to the stability of Europe’s electricity grid.

He highlights Germany as an example of a country with good connections to other countries and a high degree of stability.

Things such as electric vehicles — which can store power and then feed it back into the grid when needed — could also help provide flexibility, added Thomas. 

For regions like northern Europe, that may experience periods of little wind and sun, back up capacity, which could be provided by sources such as hydrogen turbines, may be necessary, said Pietzcker. 

Investments into renewables going strong, but more needed for grids

Electric vehicles, chips, AI and air conditioning are helping to fuel a rapid growth in electricity demand.

The technological solutions for a low carbon and stable grid are now available, said Pietzcker. “You can clearly with today’s understanding of systems, you can design stable systems that will be as resilient based on renewables.”

While grid stability is holding back the roll out of renewables in Europe a little, he says in the EU the commission is strongly pushing more interconnectedness.

The amount of investment in grids globally needs to double by 2030 to over $600 billion a year, according to the International Energy Agency. The annual investment into grids has stayed almost the same since 2010, while investments into renewables have nearly doubled.

In the wake of Spain’s blackout, Jordi Sevilla, the former president of the country’s grid operator Red Electrica, told Spanish media it was clear that the country’s grid required funding to adapt to the reality of the new generation mix.

Edited by: Sarah Steffen