Most of these issues can be improved through a combination of software and policy changes, and the report makes some suggestions in this direction.
The inertia provided by generators with lots of rotating metal (such as hydro or natural gas turbines) is generally thought to improve grid stability, but this analysis shows that even tripling the amount of inertia would have reduced system oscillations by about 3 percent. So it’s not clear that having more conventional power would help.
However, there is one area where the potential problems clearly relate to one form of renewable generation: rooftop solar. The problem is that the hardware doesn’t follow the policy, and more so the real policy doesn’t follow. Spanish grid operator Red Electrica estimates that it has about 6.5 GW of small-scale (<1 MW) solar on the grid, with 75 percent (4.9 GW) connected to low-voltage, consumer-grade grids. The committee received data from two inverter manufacturers that together monitor the performance of about 15 percent of this capacity.
These data show that a significant portion (more than 12 percent) of one of the manufacturer’s devices went offline during the first oscillations and reconnected a few minutes later. Shortly after that, more than 20 percent was closed again during the voltage peak that occurred about two minutes before the shutdown. In contrast, the share of off-grid hardware from the second manufacturer never exceeded 10 percent.
All of this suggests that while small-scale generation could see hundreds of megawatts of output jump back onto the grid within minutes of an outage, the exact numbers are highly dependent on inverter manufacturers, and the grid operator has a limited window for their actual behavior. This is a situation where increased regulation is likely to be required.
Application of learning in practice
The report is encouraging in that it identifies numerous fixes that are fairly easy to implement, including more automation of shunt reactors, wider safety margins between alarms and disconnections, and better alignment between network policy and hardware behavior. And it does not identify any critical issues that would require a review of Spain’s approach to net-zeroing its grid.
The economy will probably help the situation, too. Spain currently has very little battery capacity that can perform many functions to stabilize the grid. But the continued growth of renewables will increasingly lead to overproduction, making batteries economically unviable.
The biggest question is how quickly Spain can implement some of the report’s recommendations.
