Most of these issues can be improved through a combination of software and policy changes, and the report makes some suggestions along those lines.
The inertia provided by generators with lots of spinning metal – think hydro or natural gas turbines – is usually thought of as improving grid stability, but this analysis shows that even tripling the amount of inertia would reduce system oscillations by about 3 percent. So it’s not clear that having more traditional power online would have helped.
That said, there is one area where potential problems were clearly assigned to a form of renewable generation: rooftop solar power. The problem there is less that the hardware was not following the policy and more that there was no actual policy being followed. The Spanish grid operator, Red Electrica, estimates that there is approximately 6.5 GW of small-scale (<1 MW) solar power on the grid, with 75 percent (4.9 GW) connected to the low-voltage, consumer-scale grid. The committee received data from two inverter manufacturers, which collectively track performance at about 15 percent of that capacity. This data shows that a large portion of the manufacturer's hardware (more than 12 percent) fell off the grid during the first oscillation and reconnected a few minutes later. Shortly thereafter, more than 20 percent were disconnected again during a voltage peak that occurred about two minutes before the blackout. In contrast, the fraction of other manufacturer's hardware going off the grid never exceeded 10 percent. All this suggests that while small-scale generation can have hundreds of megawatts of output shut down and back on the grid in the minutes before a blackout, the exact numbers are highly dependent on inverter manufacturers – and grid operators have a limited window into their actual behavior. This is a case where perhaps increased regulation is needed.
putting learning into practice
The report is encouraging because it identifies several reforms that should be fairly easy to implement, including greater automation of shunt reactors, wider safety margins between alarms and disconnections, and better alignment between grid policies and hardware behavior. And it does not identify any significant issues that would require a rethink of Spain’s approach to getting its grid to net zero.
Economics will also probably help the situation. Spain currently has very little battery capacity, which can serve many purposes in stabilizing the grid. But the continued growth of renewable energy will lead to increased production that makes batteries economically viable.
The biggest question appears to be how quickly Spain can implement some of the report’s recommendations.
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