Many of these problems can be tackled with a mix of software updates and policy changes, and the report proposes several measures along those lines.
Inertia from generators with large rotating masses—think hydro or natural gas turbines—is usually credited with enhancing grid stability, but this analysis indicates that even tripling inertia would have reduced the system’s oscillations by only about 3 percent. So it’s unclear that running more conventional plants would have helped much.
That said, the report does point to one clear concern tied to a single type of renewable: rooftop solar. The issue is less that equipment ignored rules and more that effective rules are lacking. Red Eléctrica, Spain’s grid operator, estimates roughly 6.5 GW of small-scale (< 1 MW) solar on the system, with 75 percent (4.9 GW) on low-voltage, consumer-level networks. The committee obtained data from two inverter manufacturers that together monitor about 15 percent of that capacity.
Those data show that a sizeable share (over 12 percent) of one manufacturer’s devices dropped off the grid during the initial oscillations and reconnected a few minutes later. Shortly after, more than 20 percent disconnected again during a voltage peak about two minutes before the blackout. By contrast, the fraction of the second manufacturer’s devices that went offline never exceeded 10 percent.
Taken together, this suggests small-scale generation may have seen hundreds of megawatts of output drop off and return in the minutes before the blackout, with exact amounts strongly dependent on inverter vendors—and that the grid operator has limited visibility into their behavior. This is a situation where tighter regulation is likely needed.
Applying lessons learned
The report is encouraging because it identifies several fixes that should be relatively easy to implement, including greater automation of shunt reactors, wider safety margins between alarms and disconnection, and better alignment between grid policies and hardware behavior. It also does not appear to uncover any critical issues that would force a rethink of Spain’s plan to decarbonize its grid.
Economics will probably help as well. Spain currently has little battery capacity, which can serve multiple roles in stabilizing the grid. Continued growth in renewables will increasingly create surplus generation that makes batteries economically attractive.
The key question is how quickly Spain can put some of the report’s recommendations into effect.
