Comment by moffkalast
2 days ago
I'm more concerned with what happened in Spain recently when solar was peak and they couldn't correct for a voltage oscillation. Power companies keep building solar and wind with grid following inverters so there's very little frequency and voltage inertia if steam turbines aren't running. We need to start legislatively mandating grid forming inverters or flywheels or something that maintains stability or blackouts will be get more and more common as we switch over.
The Spain blackout was caused by a multitude of reasons. Lack of stability was one of the factors, but there were other causes, such as energy generation facilities disconnecting while the oscillations were still under a nominal range, or a generator ordered to become online to induce stability, that started driving the load in the wrong direction. All this was compounded by a distribution network unable to redistribute or at least isolate the problems to individual regions, resulting in a complete blackout.
All in all, it's several things that need to be reinforced. The distribution network needs to be smarter. The energy generation facilities need to be tested through their entire voltage range, so they can be counted upon. And there has to be more voltage inertia available in the network.
That is more or less the recommendation from the report, except it wasn't a shortage of intertia, more a shortage of grid voltage control, which current rules prevent renewables from participating in, even if they are capable of it (it's mostly a case of the inverters, not the panels/turbines they draw from. Same with inertia). The blackout was mainly due to a failure of multiple participants in the grid to do what they were supposed to (failing to provide the voltage control it was contracted to do, in one case potentially failing to not drive oscillations into the grid, and failing to remain online within the required voltage range). A lot of the recommendations in the report are 'we should check the plants are up to scratch'.
Yeah, I've seen this with our own solar installation - when the grid frequency dips even a bit, our house cuts itself off from the grid, including whatever power it was feeding back. It seems like a recipe for instability - grid is overstrained, so the frequency dips, and suddenly tons of distributed solar generation drops off and makes the grid even more strained.
And with UPSes that beep when they kick on, it's become very apparent that this happens basically daily during the summer, when power demand for air conditioning is high.
The investigation has shown it was in fact nothing to do with renewable energy sources despite the noise made at the time - https://www.reuters.com/business/energy/what-caused-iberian-...
It wasn't nothing to do with them, but it was mostly not to do with their intrinsic characteristics, and a lot to do with how they were managed on the grid, and how some of them were not actually acting as they should (which was also true of some non-renewable sources). Saying 'nothing to do with renewable energy sources' when the report spends half its time talking about renewable energy plants and how they contributed to the problem is really not helpful (as unhelpful, IMO, as going on about how it proved renewables intrinsically make a grind unstable, because it gives credence to that argument).
The root of the issue here is underinvestment in storage. The weather is unpredictable, but the Sun is not. It doesn't suddenly get vastly brighter. Oscillation occurs within a predictable range. But partially because storage keeps getting cheaper, countries are investing at the bare minimum right now. Why buy $100 worth of batteries today when you can get it for $80 in three years?
Batteries are also inverter based sources so they typically don't add any inertia to the grid either. It's not really about the supply of power, it's about maintaining the 50hz frequency to a 0.002% accuracy (yes really) and keeping the voltage similarly exact, otherwise things start quickly disconnecting and tripping in a chain reaction. DC sources would work much better with a HVDC grid... if we had one.
grid-scale batteries generally do add inertia, because that's the most valuable service for them to provide at a small scale. Inverters attached to batteries can do it way better than spinning generators, but they need to be set up to do that.
(And a DC grid would be much more difficult to manage: the nice thing about frequency is that it has to be pretty much the same over the whole grid, so it's a useful signal for the balance between supply and demand, while voltage is really quite sensitive to local effects)
Grid forming inverters are off the shelf technology today.
Price the ancillary services and you will be swimming in them.
> it's about maintaining the 50hz frequency to a 0.002% accuracy (yes really)
That doesn't sound right to me. In the UK the legal requirement is to be within 1% so between 49.5 to 50.5 Hz.
In operation they aim for tighter than that at +/- 0.2 Hz, so 49.8 to 50.2 Hz, or 0.4%.
I can believe that other countries might have tighter limits but not that much!