The biggest challenge is keeping the energy almost perfectly in phase. US power runs at 60Hz and most grid equipment fails quickly if that changes even a little bit.
If I'm not mistaken, that was what hit Spain when much of their grid went down for hours. The analysis I heard was that they were running entirely on renewables and it fell out of phase causing large scale safety shutdowns.
Fortunately, interconnects cannot go out of phase easily. If one region is out of phase with another, massive currents flow down the transmission lines within milliseconds, causing generators at one side or the other to slow down or speed up. I have seen this effect live at a hydroelectric dam. We were watching the turbine shaft spin at the moment they switched on some giant interconnect. There was a phase-alignment dial and it just instantly pinged up to 0 while the spinning shaft shuddered, slightly altering its rate of rotation in the blink of an eye.
Is that same functionality available in solar or wind type scenarios?
When I heard the Spain issue being described by a grid engineer, they were focusing on the lack of rotational mass in those systems compared to the large turbines used in other generator designs as the reason solar could go out of phase more easily. What you're describing sounds like that scenario, hydro has large enough rotational mass to keep things stable.
That makes sense. A single large hydroelectric turbine could generate 500MW. That’s a whole lot of power compared to a 3MW wind turbine.
That's the usual failure mode of any grid, aggressive load shedding will be used as a last resort to keep the frequency within tolerances.
The renewable aspect is because historically they were installed with "grid following" inverter systems instead of "grid forming" which can maintain frequency even if temporarily islanded in a partition without spinning mass generators to set frequency.
There's nothing intractable about a 100% renewable grid, the technology exists and has already been deployed in new installations.
Oh yeah for sure, I had assumed it was likely a transitionary issue with new systems not functioning well with older systems and different assumptions.
No this is misinformation that continues to be spread.
The Iberian blackout was caused by a lack of reactive power leading to voltages going out of their designed ranges.
The Iberian grid had adequate inertia at the time.
Reasonable grids have forced inverter based generation to manage reactive power for over a decade. But Spain due to lackluster processes relied on thermal plants to provide it. And they didn’t provide the expected amount.
There were some more confounders around oscillations and what not but the central cause came down to voltage control. Which is near trivial to solve in 2026. If you just force everyone to do it.
I'll look into this further. I heard about this from a podcast episode on The Great Simplification, I'd be very surprised if it turned out to be misinformation though its always possible. Nate is pretty damn thorough in his research and sits squarely on the left half of the political spectrum, I'd usually expect misinformation like this to come from the (US) right.
Here's the final report on the blackout from ENTSO-E:
https://www.entsoe.eu/publications/blackout/28-april-2025-ib...
From the summary on the page:
> The investigation concludes that the blackout resulted from a combination of many interacting factors, including oscillations, gaps in voltage and reactive power control, differences in voltage regulation practices, rapid output reductions and generator disconnections in Spain, and uneven stabilisation capabilities. These factors led to fast increases of voltage and cascading generation disconnections in Spain, resulting in the blackout in continental Spain and Portugal.
It even models scenarios where they double and triple the available inertia to see if it would have had any effect:
> The above analyses indicate that, even under the assumption of perfect execution of defence plan actions, neither these measures nor additional inertia would have been sufficient to prevent system collapse.
Here's the US regulation from 2016:
> As a result, all newly interconnecting non-synchronous generators will be required to provide reactive power
https://www.ferc.gov/sites/default/files/2020-06/RM16-1-000....