alt Hacker NewsThey need more battery storage for grid health, both colocated at solar PV generators (to buffer voltage and frequency anomalies) and spread throughout the grid. This replaces inertia and other grid services provided by spinning thermal generators. There was no market mechanism to encourage the deployment of this technology in concert with Spain’s rapid deployment of solar and wind.
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One problem that happened here is the _voltage_ spikes as the synchronous generation went away. Voltage _spikes_ on generation going away seem insane, but it's a real phenomenon.
The problem is that the line itself is a giant capacitor. It's charged to the maximum voltage on each cycle. Normally the grid loads immediately pulls that voltage down, and rotating loads are especially useful because they "resist" the rising (or falling) voltage.
So when the rotating loads went away, nothing was preventing the voltage from rising. And it looks like the sections of the grid started working as good old boost converters on a very large scale.
In this very specific case, battery storage would not have helped (in fact, it would have worsened the problem). One of the issues in the failure is renewables, but not because of intermittence. It's because of their ~infinite ramp and them being DC.
Anything that's not a spinning slug of steel produces AC through an inverter: electronics that take some DC, pass it through MOSFETs and coils, and spits out a mathematically pure sine wave on the output. They are perfectly controllable, and have no inertia: tell them tout output a set power and they happily will.
However, this has a few specific issues:
- infinite ramps produce sudden influx of energy or sudden drops in energy, which can trigger oscillations and trip safety of other plants
- the sine wave being electronically generated, physics won't help you to keep it in phase with the network, and more crucially, keep it lagging/ahead of the network
The last point is the most important one, and one that is actually discussed in the report. AC works well because physics is on our side, so spinning slugs or steel will self-correct depending on the power requirements of the grid, and this includes their phase compared to the grid. How out-of-phase you are is what's commonly called the power factor. Spinning slugs have a natural power factor, but inverter don't: you can make any power factor you want.
Here in the spanish blackout, there was an excess of reactive power (that is, a phase shift happening). Spinning slugs will fight this shift of phase to realign with the correct phase. An inverter will happily follow the sine wave measured and contribute to the excess of reactive power. The report outlines this: there was no "market incentive" for inverters to actively correct the grid's power factor (trad: there are no fines).
So really, more storage would not have helped. They would have tripped just like the other generators, and being inverter-based, they would have contributed to the issue. Not because "muh renewable" or "muh battery", but because of an inherent characteristic of how they're connected to the grid.
Can this be fixed? Of course. We've had the technology for years for inverters to better mimic spinning slugs of steel. Will it be? Of course. Spain's TSO will make it a requirement to fix this and energy producers will comply.
A few closing notes:
- this is not an anti-renewables writeup, but an explanation of the tech, and the fact that renewables are part of the issue is a coincidence on the underlying technical details
- inverters are not the reason the grid failed. but they're a part of why it had a runaway behavior
- yes, wind also runs on inverters despite being spinning things. with the wind being so variable, it's much more efficient to have all turbines be not synchronized, convert their AC to DC, aggregate the DC, and convert back to AC when injecting into the grid
There are non-battery buffers available too--I recently got rooftop residential solar installed, and learned that my area is covered by a grid profile requiring that the solar system stay online through something like 60 +/- 2Hz before shutting down completely, and ramping down production linearly beyond a 1Hz deviation or so. The point is to avoid cascading shutdowns by riding through over/undersupply situations, whereas an older standard for my area would have the all solar systems cut off the moment frequency exceeded 60.5Hz (which would indicate oversupply from power plant generators spinning faster via lower resistance).
In my system's case, switching to this grid profile was just a software toggle.