Stability of grids with a high percentage of asynchronous sourcing - Page 1
Forum section: electronics / general

author: AussieBruce
author_rank: Regular Contributor
timestamp: July 15, 2024, 07:22:43 am
content: I live in a country that appears to be going for broke in terms of moving to renewable generation – mostly solar and wind. Having a long background in industrial controls, I’ve tried to get hold of as much information as I can on stability of large, widely extended grids as the proportion of inverter sourcing grows. There’s a lot on the web from Texas (that state has its own grid), UTex puts a lot of informative technical stuff in the public domain. There are also a couple of local sources.My best assessment from all this is that there is still no proven configuration defined, segments of a grid can run OK on quite high percentage of asynchronous input, but they are always solidly tied to substantial amounts of proven, stable kit in the form of very large rotating generation. I’m also not aware of any instance in the world where asynchronous supply strongly dominates on its own.What’s peoples view on the current status? Is this likely to be a crunch issue down the track?

author: Someone
author_rank: Super Contributor
timestamp: July 15, 2024, 08:10:02 am
content: Quote from: AussieBruce on July 15, 2024, 07:22:43 amThat's anti-renewables propaganda, zero rotating mass/inertia/flywheel is required.Pick through a recent sealioning of the topic:https://www.eevblog.com/forum/chat/will-ac-power-distribution-become-obsolete/msg5551181/#msg5551181100% inverter grid is practical and possible today, small grids already do this and the methods/techniques perfectly scale up.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 15, 2024, 08:39:40 am
content: Zero mass/inertia might not be needed, but something has to define the base frequency and voltage.If a sole inverter grid, does each inverter sync to the existing frequency and voltage, or does it just generate at what it thinks the grid should be? What stops a drift? If each inverter runs at its own defined frequency and voltage then are there any circulating currents with a tiny discrepancy with the grid? I suppose the ultimate test is to run a synchronous clock off the grid, if it stays dead accurate then it is stable.What if a sudden load appears, lightning strike or similar, do the inverters just skip over the transients and just carry on?The grid is described as an infinite bus bar, nothing that occurs overloads it or upsets it. Is there a minimum size of inverter only grid? Obviously a rotating generator will just continue rotating and self sync.

author: zilp
author_rank: Frequent Contributor
timestamp: July 15, 2024, 09:42:39 am
content: Quote from: woodchips on July 15, 2024, 08:39:40 amThe same thing that stops drift in any other grid.I mean, I have no particular clue as far as grid management is concerned. But obviously, the equations that govern the behavior of rotating mass generators are pretty well understood. And you obviously can build a solid state inverter that just evaluates that equation to derive its control signals, and thus electrically behaves identically to a rotating mass generator, so you obviously can apply the same strategies.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 15, 2024, 10:05:01 am
content: You need to separate differences betweenfundamental issues(aka showstoppers) andcontrol algorithm details. And as explained by others, grid stability relates to the latter.It's important to realize whether showstoppers exist or not, because if they don't, then you can pretty much start transitioning, and any small issues get fixed along the way. The limited rate of change, limited by manufacturing capabilities of inverter/cell/panel manufacturing, installation/electrician resources, and people's general willingness, helps in that any such issue is caught in time and rectified. Example of such "small issue" could be an adjustment needed in default parameters that define the inverter's control curves. Or taking some small percentage of inverters (say, a few large PV parks, probably not any consumer customers) under closed loop control.

author: Someone
author_rank: Super Contributor
timestamp: July 15, 2024, 10:09:57 am
content: Quote from: woodchips on July 15, 2024, 08:39:40 amWhy does drift matter?Smells like more sealioning, as this was covered in the above linked thread:https://www.eevblog.com/forum/chat/will-ac-power-distribution-become-obsolete/msg5551223/#msg5551223Come back when you actually find some problem.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 15, 2024, 01:08:07 pm
content: The control and simulation of stability has been front of mind of grid operators for well over a decade, and the hunt for larger pools of stability analysts is still on-going. Tools and techniques continue to advance. Any new grid connect inverter has to come with an approved control simulation model. Battery grid connect systems like the large Tesla systems are approved for advanced grid support, and I'd anticipate for grid forming. South Oz often leads the way. As yet, I don't see widespread commanded disconnects of small generators, and likely for a number of reasons, even though inverters have to include that ability. It's a very large mixing pot, but mixing seems to be slow wrt electric vehicle battery integration.

author: nctnico
author_rank: Super Contributor
timestamp: July 15, 2024, 03:06:29 pm
content: Quote from: zilp on July 15, 2024, 09:42:39 amAFAIK the generators of large (hundreds of megawatts per generator unit) power plants are steered using an atomic clock to make sure that the frequency is stable long term. It is not like these generators are freerunning. The large power plants form a low impedance to which inverters can synchronise. With the large power plants gone at some point, there needs to be a way to keep the grid synchronised to an atomic clock. You can't have a large number of independent inverters pump power into the grid at any phase / frequency they like.

author: BarrowBoy
author_rank: Contributor
timestamp: July 15, 2024, 03:15:13 pm
content: Some incorrect statements, and some correct in the above. Of course a grid needs to be balanced, in time. That's why we now have negative feed in tariffs. In the UK, the are trying a novel approach. During peak generation ONLY, EV's get a free re-charge.Need to know more and stop guessing -https://us.flukecal.com/literature/electrical-calibration/testing-and-calibration-phasor-measurement-units

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 15, 2024, 03:43:22 pm
content: In fact we are talking here about two -partially overlapping- parts of net regulation.On a time scale of single seconds, you need a certain power reserve that traditionally was given by the rotational energy of the big turbines and generators. 20 years ago a lot of academic studies did research on how it is possible to transfer this behaviour into small inverters, so that also a big mass of small producers is phase-stable without a big "master generator". As far as I know these studies have been widely successful, and these technologies are nowadays obligatory for big wind- and solar farms. They practically simulate the rotating mass of generators with clever circuits and algorithms.On the next time scale you do regulation by switching loads and controlling production power where possible. This is established by higher-level communication, e.g. by internet or radio control. This is where you can catch load peaks by offering free EV-charging or ramping down a gas turbine.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: July 16, 2024, 12:35:48 am
content: https://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Security-and-reliability/-/media/80004354B88B4FEF96EAB673DDC99820.ashxQuote from: nctnico on July 15, 2024, 03:06:29 pmFrom the above PDF, the frequency's normal range control band is +/- 0.3%. Back when people wore watches, the watch crystals are accurate to 20ppm. Atomic clock not required. Over a short timescale, big power plantsarefree-running. But they have such large inertia that load changes take seconds to have an impact. Over a long term (several days) you can try and keep time with an external reference but it's absolutely not necessary in a world where nobody uses synchronous clocks any more.Grid-tie inverters cannot just "willy nilly" export at whatever phase they want, the circulating currents of an inverter trying to do that would let magic smoke out. Therefore, because they stay synchronised, they cannot "drift" away from the grid. The grid as a whole can drift, but individual generators have to stay synchronised.Grid-tie inverters synchronise with the existing waveform, and then start exporting in-phase (by locally raising the voltage ever so slightly, thus managing to push current back out). If voltage goes too high, they back off (Volt-Watt control).Modern grid-tie inverters also have Volt-Var mode. This absorbs or generates reactive power to limit voltage excursions. It also produces a leading or lagging effect on the grid, that is to change the frequency by a tiny amount. The inertia of the rest of the system limits the impact.The next step is to have some kind of frequency-reactive control. AEMO already has FCAS which will turn generators on or off, or loads on or off, if the frequency goes outside bounds. We would need something similar in distributed generation to ramp up generation when frequency is low, and ramp it down when frequency is high. Then load-shedding sort of disruptions can be avoided.As others have said, it's just a control system issue. Very easily solvable (especially since it's someone else's problem). There will likely be economic incentives for EVs to export to the grid when the grid needs energy.Quote from: woodchips on July 15, 2024, 08:39:40 amYes, then you need a gridforminginverter. A single inverter can do what it likes (if it has the capability). As soon as you have more than 1, they need to synchronise.QuoteAs above, you cannot be substantially out of phase because the circulating currents will make a rather exciting light and noise show. But yes, on a smaller scale you circulate a lot of current trying to fight the grid.QuoteDoesn't really matter. The grid can wander up and down in frequency all the time and still be stable. The point is the rate at which it wanders, and you won't pick that up with clock-watching.QuoteAn inverter "just" skips a direct strike in the same way a human "just" keeps playing golf after being hit.Depends on the size of the disturbance. Small blips will sail through, bigger blips will cause an inverter to disconnect, and it might cause catastrophic failure of the nearest few inverters.QuoteBy whom? Very simplified view, and that's useful for some analogies but important to know the limitations of such a simplistic understanding.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 16, 2024, 05:16:02 am
content: Quote from: woodchips on July 15, 2024, 08:39:40 amIt never was, and will never be. Clocks syncing onto mains were a thing of the last century, but they happily drifted by, say +/- 30 seconds, maybe even more. There was (probably still is) effort to keep grid very close to nominal frequencylong term, that is, in annual time scale, so that those clocks never need adjustments, if you are happy with significant back-and-forth drift. On the other hand, for people who like their clocks to be in correct time within a second or two, never were able to use those synchronous clocks because grid never was accurate enough on the short scale.AFAIK those retro clocks (maybe such circuitry is still used in microwave oven clocks or something, I don't know) are the only reason for maintaining long-term accuracy of the grid. Probably not many people would complain at all even if we changed grid frequency to say 50.1Hz overnight.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 16, 2024, 05:28:22 am
content: Clock syncing seems something aesthetic - if you have resources to do it then you may do it because it´s beautiful to know your grid frequency is that perfect. And old clocks run precisely.There´s not fundamental reason why you need it for power regulation or stability.

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2024, 09:30:56 am
content: Quote from: Siwastaja on July 16, 2024, 05:16:02 amYou'll be unpleasantly surprised. Every mains powered alarm clock and every other household appliance with a clock you can find in the shop is synchronised to the mains frequency because it is much more stable compared to a crystal. A couple of years ago 'our' street was running from a diesel generator for over a week because a distribution transformer blew up; the clocks where off by many minutes within two or three days.With a 50ppm crystal oscillator, a clock can be off by over 2 minutes a month. There is a good reason equipment relies on external time sources which are referenced to UTC instead of internal crystals when possible. Computers use NTP by default, mobile phones use the time from the wireless network.Where it comes to the grid frequency stability: there has to be some common ground on where to synchronise the grid to where it comes to large scale grid sources which drive the grid frequency for smaller sources to follow / track. Whether it is an NPP, gas/coal plant, storage facility, large solar park or wind farm, synchronising it to a UTC derived time source is the obvious choice. Long term stability comes with it for free.People can keep going on about long solved control algorithms but in the end they all rely on a feedback loop and thus are prone to running into stability problems when the phase margin of the control loop gets thin.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 16, 2024, 04:16:30 pm
content: Here's some data collected on grid frequency stability by some time nut:http://www.leapsecond.com/pages/mains/In general, grid frequency is extremely accurate over 24 hours, but can and will drift up and down during the day as industrial and commercial machinery is turned on and off.As mentioned above, the Australian grid has a defined specification of frequency tolerance range (as well as the more familiar voltage range 230V +10%/-6%). Your local grid will also have a defined performance specification, I encourage you to look it up.Do not assume your grid is synchronised to an atomic standard. Look up the specification.https://www.aemc.gov.au/sites/default/files/2024-01/Frequency%20Operating%20Standard.pdf

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: July 17, 2024, 01:39:02 am
content: Quote from: Andy Chee on July 16, 2024, 04:16:30 pmPrecisely.QuoteOur grid is not required to keep time.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 17, 2024, 05:56:48 am
content: Timekeeping is a convenience thing, and mains-operated alarm clock radios, while nice retro thing from 1980's, are dying out as the people who own them die. For microwave oven clocks, I would prefer them not to exist at all and I'm sure 97.5% would agree. In any case the grid never was accurate for anything else than very crude minute-level time keeping (which is why those mains-operated clocks almost never show seconds at all).Anyway, this timekeeping synchronization thing already existed in 1960's, probably even before, and AFAIK was done manually by the operators steering some of the larger plants. Like "oh, today it's 30 seconds off, let's adjust it this way..."This behavior is trivially easy to replicate on our imaginary inverter-only grid. I'm not sure if it's 1% or 10% of capacity which needs synchronization, but definitely nowhere near 100%. And just like in the 1960's, this does not involve super fast communication; no, it's more like a PI controller (or a super slow PLL) where adjustments are made in hourly/daily timeframe.All this can be implemented with a $10 GPS module and less than 100 lines of code, and only small part of producers need to implement it anyway (and it's not like the grid would collapseeven if no one did that), so it's hilarious how some people paint this as some kind of showstopper.

author: nctnico
author_rank: Super Contributor
timestamp: July 17, 2024, 08:43:07 am
content: GPS is the worst choice ever in today's world. An attacker can destabilise the grid using an SDR which can be bought for $100 from Aliexpress. Grid operators are actively moving away from using GPS for grid synchronisation because it is too vulnerable.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 08:56:43 am
content: GPS is still a good choice for reference. I´m very sure a grip operator does a plausibility check of the time data and if it´s out of tolerance falls back to some TXCO or whatever.In that case your Aliexpress powered super villain can only delay the street lighting by several microseconds. And in 99.99% of time while humanity is good you have a really precise reference clock.(PS: Probably the different levels of grid synchronization have been confusing again. Using a GPS-disciplined-XCO for phase control of the generators may seem feasible, but really would be dangerous. Using it as the time master in the grid operations center together with some backup should be easy going.)

author: Siwastaja
author_rank: Super Contributor
timestamp: July 17, 2024, 09:44:20 am
content: Quote from: nctnico on July 17, 2024, 08:43:07 amNote to others: nctnico's "destabilising the grid" means making some already inaccurate retro clocks slowly drift, timekeeping of which is not even currently being guaranteed in many (most?) countries.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 10:05:10 am
content: Quote from: Siwastaja on July 17, 2024, 09:44:20 amThat´s exactly the confusion I meant:- Destabilising the phase synchronization of single generators --> chaos and destruction- Destabilising the long-time-frequency regulation --> deviations at old clocksI think that nctnico thought of (old) plans to stabilize a grid by giving each inverter a GPS disciplined oscillator. The accuracy would be fair enough to ensure phase synchronization, but in that case a "jitter" of only a few milliseconds could indeed break down the whole grid.Nowadays the inverters are syncing themself with the grid without a frequency master. So GPS deviations wouldn't make any transformer burn.

author: nctnico
author_rank: Super Contributor
timestamp: July 17, 2024, 11:44:32 am
content: Quote from: Siwastaja on July 17, 2024, 09:44:20 amNo, not at all! As usual you are not reading /understanding correctly at all and are just gaslighting.You are confusing two things here as the discussion moves back & forth a bit. But I'll clarify for you:1) big plants which drive the mains frequency need some reference to synchronise themselves to as they have no other reference for guidance. Small inverters can track the big plants but these big plants will need to form a low enough impedance. This is simple control theory 101.2) Mains frequency is maintained to a certain frequency stability making it suitable for use as a frequency reference for clocks. As I wrote before, it is not retro clocks but modern digital clocks use mains frequency as their reference source as well. So maintaining a degree of frequency stability of the grid will be handy otherwise hundreds of millions of clocks will need replacing. Ofcourse this depends on the region where you are in. Ofcourse you are free to find it important or not but that is just your opinion. Facts are facts.

author: Someone
author_rank: Super Contributor
timestamp: July 17, 2024, 11:52:51 am
content: Quote from: Phil1977 on July 17, 2024, 10:05:10 amFrequency accuracy vs integral time error at some non specific period are nonsense arguments. Grid synchronisation and stability do not require anything more than a few cycles of the mains (100ms or so) and a 100ppm or so absolute accuracy.What GPSdisciplinedoscillator fails to maintain 100ppm accuracy during loss of satellite communications ? Laughable.No-one is trying to blindly synchronise generation without looking at the local phase.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 11:55:13 am
content: Quote from: nctnico on July 17, 2024, 11:44:32 amThis simply does not get true by repetition. "Master-less" synchronized networks need no central guidance. They can be and are stable just by solving the underlying differential equations the right way and implementing their solution into the individual control loops.It´s like waves on the ocean. There´s no "master-wave" that dictates the water molecules to go up or go down. But the system of inertia and dynamics enables them to stay in time where ever they are.Quote from: Someone on July 17, 2024, 11:52:51 amYes, but that´s exactly what would be required if a grid should break down by one failing oscillator.

author: Someone
author_rank: Super Contributor
timestamp: July 17, 2024, 12:00:30 pm
content: Quote from: nctnico on July 17, 2024, 11:44:32 amHow are big or small plants inherently any different? Either could produce accurate frequency control. Modern electronics make that practical for even small residential inverters.Quote from: nctnico on July 17, 2024, 11:44:32 amSomecountrieschooseto do this. It is not mandatory or necessary, or anything to do with grid/supply stability. One way to do this is to have generators change their operating setpoint (power output vs frequency line), which can be done slowly in some centrally co-ordinated matter if required (as it is currently done in Australia). Again residential (or larger scale) inverterscouldparticipate in this if there was economic reason to do so, it is not something preventing the share of inverter sources being increased, even to 100% of the grid.

author: Someone
author_rank: Super Contributor
timestamp: July 17, 2024, 12:08:13 pm
content: Quote from: Phil1977 on July 17, 2024, 11:55:13 amYou may need to restate that?Hard to believe a grid could (or should) fail from a single oscillator failure. A single generator might go offline, but that should not be a problem for the wider grid.People keep trying to say there is some required [long term] integral accuracy for a generators local time reference. That is untrue. Generators currently need:a) a somewhat accurate frequency reference (which is easily provided by low cost crystal oscillators) to participate in maintaining frequencyb) some way to align their rotation (synthetic or not) with the local phase before connecting powerBilling might care if it's 2 cycles past midnight, but a generator doesnt care aboutabsolutetime.

author: nctnico
author_rank: Super Contributor
timestamp: July 17, 2024, 12:18:00 pm
content: True. But imagina a long power line (say 300km) with two identical generators at each end. The impedance of the power line will be high enough that the generators can run almost at will. Ofcourse you'd start with one generator and the other one can be started in sync (to match the phase), but once running at full power the synchronisation effect won't be very strong. And which one is the leader?A similar effect can be observed with classic ethernet or long RS485 busses. Two stations far apart can start transmitting without detecting the other one is garbling the messages due to the impedance of the transmission line.See this presentation:https://wsts.atis.org/wp-content/uploads/2021/03/Challenges_to_Updating_Timing_In_The_Power_Grid.Jones-Shoenwald-Tuffner.pdfAnd NIST also published a report on time synchronisation needed to monitor the grid stability:https://nvlpubs.nist.gov/nistpubs/specialpublications/nist.sp.1500-08.pdf

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 12:34:08 pm
content: Quote from: nctnico on July 17, 2024, 12:18:00 pmIf the line impedance would be that high you couldn't operate a power grid at all, this would mean that not much power is transferred at all.If both generators have a good coupling by a low-impedant grid (as a grid needs to be) they keep themself in sync. You could do the maths, or to make it easier you can imagine that even parts of a degree of phase mismatch would induce a high reactive power over the grid line. This reactive power slows one generator down and speeds the other one up - up to the point when they are in sync again.You can reproduce exactly the same electrodynamic behaviour with electronic inverters. Mechanic assemblies with large inertia make it better descriptive, but the principle is exactly the same.Quote from: nctnico on July 17, 2024, 12:18:00 pmOkay, now I see the problem: We we´re talking in this thread aboutpower generation. NIST is talking in the paper aboutpower distribution.If you want to do power distribution with a large scale grid that has to cope with phase mismatch by lines of different length and impedance and homogenizing the flow of power over the available lines, then things are infinitely more complicated. But there are very smart people (e.g. at NIST) who will take this challenge.But for the sourcing itself - keep things easy!

author: nctnico
author_rank: Super Contributor
timestamp: July 17, 2024, 12:53:19 pm
content: In the end grid based power generation and distribution go hand in hand. Potato potaato

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 01:19:11 pm
content: Quote from: nctnico on July 17, 2024, 12:53:19 pmGeneration, distribution and consumption should even go hand in handNo one says precise timing is not important - but it´s no special problem of de-central generation.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 20, 2024, 12:07:26 pm
content: Rather than try and remember stuff from years ago, I have trawled through many relevant books. These are all 50-100 years old.There is no central reference voltage or frequency on the grid. It is distributed amongst all the generators. In the UK typical consumption now is about 30GW, so even the largest 1GW generator is very small, so no individual generator can vary either voltage or frequency. This is what is called an infinite busbar.All power stations read the current busbar voltage and frequency. If any change is needed then many have to work together.The only way to alter voltage or frequency is to increase or decrease the steam going to the turbines, many or them. The system inertia is such that a change is only possible after many minutes or hours.I assume that frequency is measured by cycle counting, say for 10 minutes it counts every cycle and stops, it should be 30,000 so easy to decide whether you need one or two cycles up or down. And that is the stability that is looked for, all the synchonous clocks need to keep time.Now that renewables have arrived, then all the photos I have seen of wind turbines have a rotating alternator/induction generator so they aid the frequency stability of the grid. An inverter is a different thing altogether, there is no inertia in it at all. So it must sample the connected grid to obtain frequency and voltage, then equal it. This does not work if all the rotating generators suddenly disappear.This is more complex than it seems, an overhead line is limited to about 100 miles but even that will have a noticeable phase shift, only 1 degree will result in lots of losses and heat. So if you have inverter farms that far apart then how do they synchronise, atomic clocks seem useless, they are not accurate to the line state at each end.Is this one of the new fangled whizzy improvements, rotating metal to inverters, that aren't quite so red hot, literally? Bit like mass software updates?It is interesting though, keep the comments coming please.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 20, 2024, 12:31:32 pm
content: Quote from: woodchips on July 20, 2024, 12:07:26 pmIt's completely beyond me why people keep repeating these lies, like parrots, despite these have been shown complete lies dozens and dozens of times, in every threadPlease just stop.Given that inverters have already implemented these inertia-emulating curves for many years (another question is, is that all currently enabled, because there is still little need), this is really getting into "look at this flat earth" territory.Quote from: woodchips on July 20, 2024, 12:07:26 pmThis idea of somehow having to synchronize inverters into operating in lockstep and compensating some power transfer delay is absolutely ridiculous - obviously other types of generators never did this either. Because these idiots parrotting it never stop regardless of how many times they have been shown being wrong, I'm now more interested about where is this idea originally coming from? It's weird enough I don't believe so many people have come up with it independently.In other words, I'm saying this is probably some kind of semi-organized propaganda. I might be wrong though.

author: Marco
author_rank: Super Contributor
timestamp: July 20, 2024, 12:48:14 pm
content: Commercial system, not research.https://www.fimer.com/sites/default/files/FIMER_Brochure-Utility%20Applications_EN_revB_1.pdf"Full four quadrant active power and reactive power support"It's not a complete multi-functional inverter, but the systems can already provide power support (ie. sink a bit during the cycle). If the electricity companies want more, they should just demand it from utility scale solar. Technology is ready.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: July 20, 2024, 01:20:48 pm
content: Quote from: woodchips on July 20, 2024, 12:07:26 pmThe wavelength of 50Hz at the speed of light is 6,000km. 1 degree of phase shift is 16km. So if 16km is enough phase shift to cause problems, how does anything work at all?100 miles, or 160km, would be 10 degrees of phase shift. That sounds quite catastrophic. Except... it isn't. There are many overhead lines that span substantially more than 160km.I suggest there is a logical fallacy in your reasoning somewhere.

author: zilp
author_rank: Frequent Contributor
timestamp: July 20, 2024, 02:40:12 pm
content: Quote from: Siwastaja on July 20, 2024, 12:31:32 pmIn particular: It has been explained in this very thread, repeatedly.And not only that, it is also just obvious that it is nonsense. Like, how does anyone who has any idea how an inverter works even get the idea that it somehow could be impossible for an inverter to change output power based on grid frequency fluctuations?!But, yeah, I agree that it is the perfect propaganda lie: People interested in technology might have heard that the inertia of rotating masses in thermal power plants stabilize the grid, and obviously, your typical solid state inverter doesn't have any rotating mass ... so, that's probably an effective hook to make people who lack any deeper understanding believe that therefore, inverters can't stabilize the grid, and that they are smart enough to understand this while everyone else is blind to this truth because they don't understand technology, which immunizes them against criticism against their position, because that criticism then must be motivated by the "green ideology" of people who don't understand technology ...

author: Siwastaja
author_rank: Super Contributor
timestamp: July 20, 2024, 05:21:34 pm
content: Quote from: Marco on July 20, 2024, 12:48:14 pmThis has even been a legal requirement for a long time, IIRC from 2010 or so in Germany for example. More than 10 years!Every cheap Chinese inverter (e.g. Solis datasheet in attachment) can participate, either by being configured with a fixed phase shift; or, if at some point it seems necessary to add centralized control for a swarm of smaller inverters acting towards the same goal (which could be useful for long-term frequency stabilization, the thing for those retro clocks), then small IoT dongles with MODBUS/RS485 can be simply added. In fact most of these inverters are already in manufacturer's cloud service (because installers can that way monitor and debug).And to be clear, every generator - inverter or rotating -hasto synchronize to the grid (just by sensing the local grid voltage, not by some weird timing-critical communication scheme), and only havetwoparameters to control, both slowly varying (within seconds): real power output, and slight adjustment to reactive power (lagging or leading power factor). That's it. Traditionally these parameters were controlled by actual people in control rooms based on some very simple rules of thumb. This is all trivially easy to algorithmically replicate and this has been done decades ago.

author: Someone
author_rank: Super Contributor
timestamp: July 20, 2024, 11:18:00 pm
content: Quote from: Siwastaja on July 20, 2024, 12:31:32 pmIt doesnt help when the operators simplify it down to that "doesnt work" claim:https://www.nationalgrideso.com/electricity-explained/how-do-we-balance-grid/what-inertiaWhich is untrue, out of date, yet convenient to protect entrenched investments/decisions.Yet in other publications the same organisation is proposing? currently? using inverters for the inertia:https://globalpst.org/wp-content/uploads/ESO-inertia-management.pdfhttps://www.nationalgrideso.com/document/278171/download"GFC"/"GFM"/"VSM" all having been demonstrated and known to be practical, by ESO.

author: .RC.
author_rank: Frequent Contributor
timestamp: July 21, 2024, 03:57:09 am
content: All I know is I expect down the track with millions of generators all connected together all relying on third party support there will be a huge catastrophe as there will be an event that will wipe a lot of these micro generators out, parts will be impossible to come by to repair.The KISS theory has well and truly been thrown out the window by this rush into wind, solar and what not.

author: zilp
author_rank: Frequent Contributor
timestamp: July 21, 2024, 04:25:51 am
content: Quote from: .RC. on July 21, 2024, 03:57:09 amAll I know is I expect down the track with millions of generators all connected together all providing each other support there will never again be a huge catastrophe as there will never be an event that will wipe a lot of these micro generators out, so availability of spares doesn't matter much.Luckily, I can just make stuff up to cancel out the stuff that you make up.Now, can we get back to falsifiable theories of grid operation rather than ideologically informed gut feelings?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 21, 2024, 05:08:02 am
content: Quote from: .RC. on July 21, 2024, 03:57:09 amSpotted the exact lie injected here. In reality, obviously solar inverters work independently, without any support, communication, updates or whatever.

author: .RC.
author_rank: Frequent Contributor
timestamp: July 21, 2024, 07:26:13 am
content: Actually I meant in the case of Australia absolutely everything is made overseas, so we are reliant on third party countries, some of which hold expansion plans.I do not think we could make a SMD resistor here. Or maybe one company in Sydney can.We certainly could not make an inverter from local parts. These "big batteries". Someone could go out with a gun with silencer and subsonic ammunition and easily take out an entire storage facility without anyone any the wiser.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: July 21, 2024, 08:00:08 am
content: Quote from: .RC. on July 21, 2024, 07:26:13 amYou're reliant on so many 3rd parties you take for granted already. Can any of us survive completely independently of others? I doubt it. I wouldn't have the first idea how to feed myself from first principles and I hope I never have to try.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 21, 2024, 08:43:09 am
content: Some more comments. Why can't someone describe, in words of one syllable, the process by which inverter number 53 syncs itself to the other 52 on a local grid. The abuse really doesn't get anyone any further, I have spent lots of time reading books about the start of the grid and how the people then tried and tested to prove that, yes, you could connect synchronous generators in parallel, but not series.What it the normal size of inverters? If they are ones off solar panels then 10kW seems to be it, if a reverse car battery charger then 100kW is possible. These are peanuts compared to almost any rotating generator. Doesn't this huge reduction in the size of each individual energy source cause problems?Even with modern inverters, if you get your voltage to be different to the grid voltage then current will flow, somewhere. So, again, in words of one syllable why not explain how the tiny little inverters cope with this voltage difference. Of course in a rotating grid there are just two controlling adjustments possible, steam and excitation, what replaces these?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 21, 2024, 09:23:19 am
content: Quote from: woodchips on July 21, 2024, 08:43:09 amIt's simple: it doesn't. It only syncs to the voltage it measures right where it is connected.It can be as simple as measuring voltage, and controlling current controller's setpoint to be in direct relation with measured voltage.It can work as simply as this:* Measure instantaneous line voltage (e.g. 100V)* Multiple this by a constant, say 0.1, to decide injected current. e.g. 100 * 0.1 = 10 (A)* Set current controller loop to output 10A* Current controller measures current through a shunt resistor and sees less than 10A going* A transistor is turned on, and current through the inductor in the converter starts to rise* Once 10A is flowing, transistor is turned offRepeat this process thousands of times a second, and you have an inverter which "syncs to grid" and outputs power with PF1.0.The above constant, 0.1 in this example, needs to be adjusted in a slowed control loop so that proper PV DC input voltage is maintained.This is all electronic equivalent to what rotating machines do. They also sync themselves to the grid locally.Quote from: woodchips on July 21, 2024, 08:43:09 amBy Ohm's law, yes. This small voltage difference is what "drives" current, in all power distribution systems, AC or DC. Or you can swap the thinking around and say that driving current into lines causes a small voltage drop; the same thing. It is just how it works. It is interesting how you find somehow the fact that there is current flowing in power grid somehow weird or problematic to mention it like this. I think to many, even complete laymen, it is obvious that current is flowing in power lines (grid or their home wiring).

author: gf
author_rank: Super Contributor
timestamp: July 21, 2024, 09:23:47 am
content: Here is an overview of control methods for grid forming inverters:https://www.mdpi.com/1996-1073/13/10/2589Conventional small grid-tied inverters are, however, not grid forming, but their control loop rather makes them behave like an AC current source, where the injected current is phase-locked to the grid voltage (possibly with some phase offset, if the inverter is supposed to supply reactive power).

author: zilp
author_rank: Frequent Contributor
timestamp: July 21, 2024, 10:29:35 am
content: Quote from: woodchips on July 21, 2024, 08:43:09 amIt does so by means of a PLL, usually implemented in software.It's not that you are wrong when you say that the inverter "samples the grid to obtain frequency and voltage". Your error is in assuming that a turbine/generator machine doesn't do the same. When you bring up a rotating generator, you also regulate its rotation rate until it is in sync with the grid, then you connect it. It's no different with an inverter. The only difference is that the inverter has basically no limit on how fast it can adjust frequency and phase, so an inverter can in principle achieve grid sync in a few milliseconds, which a rotating generator can't do.Quote from: woodchips on July 21, 2024, 08:43:09 amWhat problems?Quote from: woodchips on July 21, 2024, 08:43:09 amThey don't "cope" with anything, the creation of that voltage difference is their job, if they didn't create a voltage difference, they wouldn't work.I'm not sure what your idea is of how an inverter works, but an inverter certainly doesn't have some kind of fixed output voltage that then can somehow be massively mismatched with the grid, if that is what you are thinking!?The inverter output stage has a power target (that is determined, in the case of solar inverters, by the MPPT of the input stage) and will thus create sufficient voltage to push that much power into the grid. How much voltage that is depends on the voltage and impedance of the local grid connection and will be regulated cycle by cycle. Necessarily, the voltage needs to be higher than the "idle" voltage of the connection, or else no power would flow into the grid. The inverter will simply continuously measure voltage and current and will adjust the voltage such that the product of voltage and current matches the power target. At the same time, it will monitor the voltage so as to not exceed certain limits, and will reduce or completely disable output as needed.There isn't really any "replacement for steam and excitation", simply because these aren't mechanical systems. This is software running on a microprocessor that switches power transistors on and off in order to achieve the desired voltage and current wave forms. Also, having to regulate steam and excitation is not somehow a great feature of thermal power plants, it's rather a limitation, so it doesn't make a whole lot of sense to want to replace them. What you are actually trying to regulate is the voltage and frequency/phase of the electrical output. With thermal power plants, you only can do that the roundabout way of changing steam and excitation. With an inverter, you can just change them instantaneously if you write the software that way. Or you can change them slowly, if you write the software that way. An inverter can simply change power output rapidly, cycle to cycle, something that no thermal power plant can do, and it is all up to the software how you regulate power output.

author: Someone
author_rank: Super Contributor
timestamp: July 21, 2024, 10:43:09 am
content: Quote from: woodchips on July 21, 2024, 08:43:09 amThe onus is on you to explain why a collection of smaller generators causes problems. Asking others to find justification for your unsupported ideas just points to your inability to even enter the conversation.Quote from: woodchips on July 21, 2024, 08:43:09 amHow is this any different to a grid with numerous rotating mass generators? You have chosen to say there is some distinction, but have not pointed to any.Quote from: woodchips on July 21, 2024, 08:43:09 amThe grid as a system has no concept of those, it cannot be reduced to "just two" things and certainly not to those things.

author: Someone
author_rank: Super Contributor
timestamp: July 21, 2024, 10:57:14 am
content: Quote from: gf on July 21, 2024, 09:23:47 amThis is part of the subtle differences that are easy to produce misleading comments from.That existing inverters (generally) have not provided frequency inertiadoes not implythat inverters alone cannot provide inertia to fully support the grid. A grid without any rotating mass is known to be practical with today's technology, and has already been demonstrated. For most inverters thats just a change of control parameters or a software update away, the physical capability is already out there.I'll strongly disagree with that linked papers binary distinction of gird forming [voltage controlled] vs current controlled, as current controlled inverters are equally capable of producing frequency inertia with suitable PLL tuning (which is/was explicitly prohibited by grid operators).

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 21, 2024, 05:27:43 pm
content: Even if for some hypothetical reason a grid would need rotating mass you could install so called "synchronous condensors" which principally are just a large electric motor / generator connected to the grid. In the grid or in industrial applications they are used to reduce reactive power end enhance grid transmission efficiency:https://en.wikipedia.org/wiki/Synchronous_condenserThis device has a large rotating mass that acts as a kind of flywheel with a certain level of rotational energy. If voltage or current in the net are out of phase, or if load spikes need to be dampened then energy is fed into or taken from this flywheel.It´s really not difficult to setup a good physical model when electricity needs to be converted into rotation or when it´s necessary to generate electricity from rotation. You can take exactly these rules to build a circuit that stores or takes energy from a big capacitor.This is - extremely simplified - what's done in grid stabilizing inverters. You have a well buffered DC bus that can feed the grid with power exactly when a beautiful sine wave needs it - or even take momentary power in certain circumstances.You don't need an atomic clock or anything very exotic for this. The capacitor you need in the inverters isn't even that big, not much more than you anyhow need for the conversion circuit.It´s sad but true that many people nowadays are afraid of the future and think they can keep anything as it is by denying progress. They just say progress is impossible because they are afraid of it. And to justify this some people shamelessly lie and other frightened people spread these lies. This grid stability thing is one of these lies.

author: nctnico
author_rank: Super Contributor
timestamp: July 21, 2024, 06:41:36 pm
content: Quote from: Phil1977 on July 21, 2024, 05:27:43 pmBut this is what I've been claiming all along: you will need devices to govern the grid stability regardless how they are physically constructed. Decentralised generation or not, there have to be devices which govern synchronisity. Like an orchestra needs a director. But those grid synchronising devices will need to be loud enough to overcome the noise as each micro inverter feeding the grid adds noise due to component tolerances and measuring errors.And for sure you don't need an atomic clock perse, but it certainly is a nice to have as even today clocks depend on the grid frequency being stable most of the time.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 21, 2024, 08:17:57 pm
content: Quote from: nctnico on July 21, 2024, 06:41:36 pmThe comparison with an orchestra and a director is nice - because (as far as I know) the instruments in an orchestra more or less synchronize themselves too. They don't look at the director to know which note has to be played. But the director gives some advice and guidance to make everything perfect.In the grid that means: You don't need very big central instances for the buffering. Thousands of medium sized inverters can do the trick together. It doesn't matter if you have one large mass of inertia or thousand small ones.Of course you need some supervising power - each grid has some central office that plays the director and does the checks and balances. For this purpose it´s definitely good to have precise measuring instruments incl. precise clocks. And no one seriously doubts supervising a grid is complicated - I think not even whole EEVBlog will know everything you have to care about there.But luckily it´s just not true that our wealth and grids purely rely on coal or uranium hungry energy monsters.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 21, 2024, 10:13:31 pm
content: Quote from: Phil1977 on July 21, 2024, 08:17:57 pmAnd incidentally, any one who has experience of conducting an orchestra or choir on the first day of rehearsals, would know how unstable they can be!

author: Someone
author_rank: Super Contributor
timestamp: July 21, 2024, 10:28:07 pm
content: Quote from: nctnico on July 21, 2024, 06:41:36 pmA rather long bow to draw, just to inject your disingenuous points.Noise is not a problem when it is adding together a large number of unbiased noise sources, that averages out to "nothing". If any specific generator has a local clock frequency error, all that adds is a small change in the power it is delivering to the grid. Which is fairly metered, and the only problem is that generator might be contributing (and being paid for) less energy than they otherwise would be entitled to generate. No grid stability (that inertia could protect from) is lost from inaccurate clocks, only long term frequency accuracy could be affected and thats assuming there was zero action taken by the grid operators (which is unbelievable).Using a non-specific "stable" without any qualification of what time scale that is continues your patterns of dropping half an argument and coming back to point out how people mis-interpreted you. Troll behaviour. Grid instability (inertia relevant timescales of single cycle to seconds) from inaccurate clocks would require something unbelievable like sudden/instantaneous multiple percent changes appearing in local oscillators, implausible and if that was normal/typical for the device it would fail compliance testing before being deployed.Synchronicity (an antonym to what you likely mean): "the simultaneous occurrence of events which appear significantly related but have no discernible causal connection". Rather the grid synchronisation is by design and a simple causal relationship.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 21, 2024, 11:11:45 pm
content: Haven't read every line of this whole thread, but it seems to me there are some missed points and clarification needed. Referring to a concept from early in the thread, I am not aware of any fundamental issues that prevent a solution. But there are very real implementation issues, most of which have theoretical solutions not all of which are fully implemented as renewables exist today.Issue 1. As the solar system in my home is configured (and probably most grid tied systems in the world), when there is a fault on the incoming line the system disconnects from the grid. This is done for the safety of grid workers as they repair the fault. It is bad for linemen when they find a "disconnected" line energized by attached renewable sources. This doesn't cause any really serious problems when renewables constitute a small fraction of total generation. But when that proportion becomes significant there are various issues. When the fault is due to one of the remaining large singular generation sources failing the effect is magnified by the loss of all the attached renewable. And there are startup problems. There are lots of ways to solve this problem, but to my knowledge there isn't much effort yet on implementation. As mentioned previously, no one wants to pay for it.Issue 2. DC grids are not automatically stable. The issues are different, again all solvable AFAIK. But there has been next to no investment in DC grids with more than a few dozen sources and sinks. Even fewer where operations are split over a huge number of owners and organizations.Issue 3. Something I am surprised that no one in this forum has brought up is filtering for the noise caused by power lines. I have several pieces of equipment that have notch filters for power line frequency. If power line frequency is allowed to drift widely from current norms these filters will be noticeably less effective. There are other effects from allowing large drifts in frequency, mostly involving changes in line loss, reactive power and core loss in equipment that is often carefully optimized for one frequency. Equipment from a 50 Hz network usually works on 60 Hz and visa versa, but not as well. Clocks are not the only reason to keep power line frequency relatively constant.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 21, 2024, 11:24:15 pm
content: Speaking of synchronisation:The metronomes are analogous to conventional spinning turbines due to their pendulum weight providing the equivalent of inertia.The metronome equivalent of an inverter would be a HDD voice coil head ticking back & forth. i.e. no inertial mass, and would rely on sensors to detect and trigger the voice coil.

author: Someone
author_rank: Super Contributor
timestamp: July 22, 2024, 01:09:56 am
content: Quote from: CatalinaWOW on July 21, 2024, 11:11:45 pmWell perhaps you should?Quote from: CatalinaWOW on July 21, 2024, 11:11:45 pmNo-one is seriously suggesting frequency deviations larger than already exist:https://www.eevblog.com/forum/chat/will-ac-power-distribution-become-obsolete/msg5550023/#msg5550023The existing grid will basically collapse (by design) when frequency is off by a few percent, that is considered gross fault. Load shedding (emergency intervention) is usually starting at 1% deviation.Quote from: CatalinaWOW on July 21, 2024, 11:11:45 pmAnti islanding is (almost entirely) administrative/regulatory control demanded by the grid operators. Grid operators have and do license inverter systems to provide virtual inertia but so far this has only been larger "centralised" plants which can be commanded like existing generators. 99% of the problem preventing inverters participating in inertia is grid operators demanding extremely fast anti-islanding.Non-trivial grids have already operated with insignificant amounts of mechanical inertia:https://spectrum.ieee.org/electric-inverterThat an inverter can be configured to emulate the dynamics of existing plant (which they can) is all that is required for them to incrementally replace existing mechanic inertia. Known/proven/deployed already, there is no question of "can" inverters provide grid stability, it is only a question of how they will be integrated/compensated/economical.

author: zilp
author_rank: Frequent Contributor
timestamp: July 22, 2024, 03:12:01 am
content: Quote from: Andy Chee on July 21, 2024, 11:24:15 pmI mean, that's kinda a useful analogy ... but also not. Because the important question is not whether there are "sensors" involved. The important question is whether the bandwidth of the regulation loop is sufficient. And there is no fundamental reason why things should be too slow just because electricity is involved.After all, if you were to use a voice coil with some high resolution position encoder and high-bandwidth error amplifier, you can get it to be pretty stiff, too. AIUI, that's not what modern HDDs do, probably because they need extremely high positioning accuracy ... but then, you don't need to control mains voltage to microvolts.So, it's not necessarily a bad analogy, but also, it doesn't really give any useful insight into the stability of inverter driven grids.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 22, 2024, 06:19:19 am
content: Quote from: Andy Chee on July 21, 2024, 10:13:31 pmAnd no one says that first studies with grid forming inverters did not release lots of magic smoke and have blown a lot of fuses.But these rehearsals proof now successful for quite a long time.As far as I know there was no black start of a really large grid like North America or Europe yet that was initiated by inverters. But that´s probably not necessary at all in future. Here in Germany we usually plan with hydroelectricity and gas turbines to start the segments of the net and then incrementally switch on loads and other generators. These plants won't vanish from large grids very soon.How to re-synchronize different areas of the grid after loss of synchronization is another complicated topic, it´s practised not often but it was always done reliably.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 22, 2024, 10:22:46 am
content: Quote from: CatalinaWOW on July 21, 2024, 11:11:45 pmThat´s a really interesting topic. DC grids for long distance transfer seem very tempting regarding efficiency and possible power levels. But investments to get this stable would be huge, no one wants the be the first. That makes it even less desirable for intermediate distribution levels.Transformer based AC grids are there, are well-known and physically quite rigid. It´s very understandable no one wants to abandon such a well working system. But maybe in a distant future with certain countries exporting huge amounts of PV or wind energy, maybe then a big high voltage DC bus gets attractive to build.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 22, 2024, 01:37:49 pm
content: Quote from: Someone on July 22, 2024, 01:09:56 amPerhaps you know that the person who suggested that deviations of ten Hertz in this thread didn't matter wasn't serious. I don't. And perhaps this comment will tell you that I did read almost every line.I will repeat that I agree that all of the problems have solutions. But your comment that the problems with islanding are legislative and therefore some not real is strange. A non-technical problem is still a real problem, and will require time and investment to correct. Investment in changing the laws and investment in retrofits/adjustments to the the growing existing infrastructure.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 01:48:06 pm
content: Quote from: CatalinaWOW on July 22, 2024, 01:37:49 pmBut islanding is a technical problem. If an island forms you can't shut down the power for maintenance work, so you have a massive safety problem.... or is fried technicians not a technical problem? They could wear extra PPE, I guess. The legislation specifically responded to a technical problem.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 22, 2024, 02:17:48 pm
content: This islanding is an organizational problem in the worst case.The small inverters you have in a single buildings usually don't generate much more power than they consume. They do not need to care for grid stability.What it´s all about are the medium sized generating units. Like "agricultural" solar farms, wind farms, larger combined heat and power - just by gut feeling I´d say everything >500kW. These units need to be managed in a way that they form a stable power backbone.Probably you can limit this inverter quality to everything connected to the intermediate voltage level grid. And there you need strict organizational safety measures to ensure safe conditions for any kind of technician in any case.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 03:15:20 pm
content: Quote from: Phil1977 on July 22, 2024, 02:17:48 pmHow is the power not being guaranteed to stop when the grid operator turns it off for maintenance or an emergency an organisational problem? Is your idea of organisational that maintenance only occurs at night, when the sun doesn't shine, and every source can be expected to drop out? Battery storage has made even that a bit dodgy.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 22, 2024, 04:28:37 pm
content: Islanding is a technical problem. The legislative problem is that the solution it forced is driven only by safety, the legislation does not prepare for large amounts of small solar systems.I believe my system is somewhat typical. It is designed to draw zero energy from the grid when averaged over a one year interval. Which means there is a large excess of power generated during peak months. And while the system is trivial in size from the standpoint of a utility (peak output is around 12kW) penetration of these small systems is growing rapidly. I am sure there are hundreds within 50 kilometers of me, and if penetration grows to the 20-50% level you will be talking tens of thousands of these small systems with total peak capacity measured in megawatts.Whether this kind of growth actually occurs is unclear. With current pricing (both on the solar side and utility rate side) it makes economic sense to install solar, but the high upfront costs and relatively long payback interval definitely is a barrier to adoption.But the real barrier is the same one driving utility scale adoption of solar. If renewables are ever to be a huge part of the total electrical system the seasonal availability of these sources needs to be addressed. There are three solutions I am aware of; sizing the system (solar or wind) to meet requirements in the worst case season, developing season level storage capacity, or developing transcontinental grids some part of the grid is always in favorable conditions. The investment for none of those approaches is currently planned. At my location the available solar in the dead of winter drops to 10% or less of the peak summer power. That level of increased capacity makes solar dramatically more expensive than even nuclear. Seasonal storage makes that option look cheap. Transcontinental grids appear to be the cheapest solution, but I see no planning for this approach, and little prospect for the level of international cooperation it would require.

author: tszaboo
author_rank: Super Contributor
timestamp: July 22, 2024, 05:05:30 pm
content: Quote from: woodchips on July 20, 2024, 12:07:26 pmNever mind the central frequency issue.How do you restart the grid in case of a backout? Imagine a cable was cut, and parts of the country goes black.Instead of 20 power plants, that will generate electricity on command, you have a million inverters. All of them will say that they are in islanding mode, and don't generate electricity. You need to increase the voltage on the line (while load is still connected) to 200V or so for the inverters to start exporting electricity.How do you do that? Maybe we should keep a few nuclear power plants just in case.

author: nctnico
author_rank: Super Contributor
timestamp: July 22, 2024, 05:13:53 pm
content: Quote from: tszaboo on July 22, 2024, 05:05:30 pmWell, the scenario for this would be to start with one primary, grid forming source (fossil, wind, solar, hydro, nuclear or storage; doesn't matter for as long as it is big enough) and bring up the other primary (grid forming) sources one by one so they can all align their phase & frequency. Once the core grid is powered up and stable, then connect the consumers gradually. At that point the grid tracking sources can start pumping energy into the grid.

author: zilp
author_rank: Frequent Contributor
timestamp: July 22, 2024, 05:22:32 pm
content: Quote from: CatalinaWOW on July 22, 2024, 04:28:37 pmOver here, we havemorerenewable enery in the winter than in the summer, because wind is generating so much more in the winter.So, no, you don't need "seasonal storage", at least not in the sense of "storing all the energy you need for winter", and you also don't need to overprovision solar by a factor of 10. You just need a good mix of sources plus some storage.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 05:32:52 pm
content: Quote from: zilp on July 22, 2024, 05:22:32 pmWhat an incredible dumb thing to say. First you refer to your own circumstances, then you try to generalise what works for you to be something that works for others. RENEWABLES DON'T GENERALISE. Every spot on the planet brings its own benefits and challenges.

author: zilp
author_rank: Frequent Contributor
timestamp: July 22, 2024, 06:54:04 pm
content: Quote from: coppice on July 22, 2024, 05:32:52 pmIt's just that this generalizes relatively well. Yeah, of course you don't have more wind during winter at the equator ... because you don't have winter.But also, I was specifically responding to CatalinaWOW, who happens to have a US flag next to the name, and for large parts of the US, this should apply.Also, the point wasn't primarily that everyone has more renewables during winter, but that wind tends to be negatively corralated with sunshine, so it's not like you can't have renewable power when the sun isn't shining ... to the point that at least in some places, you actually have more renewables during the winter, despite what many people believe.Really, hydro power is way more variable across the globe.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 07:06:54 pm
content: Quote from: zilp on July 22, 2024, 06:54:04 pmHaving the US flag beside his name means he could live in absolutely any kind of climate. Desert. Perpetual ice. No wind. Endless wind. No rain. Endless rain. You name it, and some part of the US experiences it.

author: Someone
author_rank: Super Contributor
timestamp: July 22, 2024, 10:29:45 pm
content: Quote from: CatalinaWOW on July 22, 2024, 04:28:37 pmNote that most of the "gird scale" inverter connected plants of x00MW (or aggregates such as wind farms) also have the same rapid anti-islanding and fault disconnect requirements as xkW domestic installs. It is crazy and purely administrative as those larger inverter installations already get two-way communications for power dispatch, so could participate in inertia/stability if permitted by grid operators.Inverters providing stability services is mature technology, 6 years of operational history:https://www.electranet.com.au/electranets-battery-storage-project/Quote from: tszaboo on July 22, 2024, 05:05:30 pmThat depends on how much of the total generation is coming from those "millions" of small inverters. Grid scale (x00MW) inverter installations are about equal to the highly distributed (20kW or below) plants in the Australian grid at the moment. No problem there to black start with a subset of grid scale operating as grid forming and slowly re-connecting the others to return to full connectivity. Thats before improving the stability participation of the smaller units, which would make it easier.

author: Someone
author_rank: Super Contributor
timestamp: July 22, 2024, 10:45:05 pm
content: Quote from: zilp on July 22, 2024, 05:22:32 pmUS government bodies are planning around needing a huge increase in transmission capacity to support just that:https://www.nrel.gov/docs/fy22osti/81644.pdf"Examining Supply-Side Options to Achieve 100% Clean Electricity by 2035"That has surprisingly little storage and less over provision than I would expect. Somewhere around 3x over provision in wind is already approaching the reliability of fossil plants before any other contributions.Interestingly nowhere did stability/inertia/FCAS come up as an issue in that report. They missed a huge hole in the analysis? or its a non-issue? I'm going for that second one.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 22, 2024, 11:11:02 pm
content: Yes, I identified my local circumstance. In a valley in the northern part of the US. And I agree that it is all local. So suggesting that places that have wind resources in winter when solar is weak is just as wrong. Where I live now has no meaningful wind resource at any time of the year. My previous residence (closer to the equator) came closer to a year round balance. Although wind was also zilch there year round usage peaked in summer when solar resource was highest. But unfortunately winter resource did dip below winter production implying something else to bridge the gap.Even places with well balance resources (Wind in the winter, sun in the summer) will have resources out of balance for periods of weeks or even months requiring some form of supplement whether it is importation, storage or other means of generation.

author: zilp
author_rank: Frequent Contributor
timestamp: July 23, 2024, 04:40:18 am
content: Quote from: CatalinaWOW on July 22, 2024, 11:11:02 pmIs this as in "we are surrounded by mountains, so no wind down here", i.e. "we could put wind turbines on top of the mountains and have plenty of wind power"?Quote from: CatalinaWOW on July 22, 2024, 11:11:02 pmYes, of course. But nothing coming close to "storing the energy needed for half a year".

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 23, 2024, 04:27:41 pm
content: Quote from: zilp on July 23, 2024, 04:40:18 amYes mountaintops are windy. But are also hard to get to, farther from points of use and generally have either no roads, or roads not suitable for transport of large objects like windmill components. None of these are showstoppers, but they all translate into very significant costs.I also agree that storage for half a year is seldom required. But the storage required can't be waved away as "far less than half a year". There is either an incredible leap in technology required or very sizeable investments in currently available technologies.

author: nctnico
author_rank: Super Contributor
timestamp: July 23, 2024, 04:49:11 pm
content: Quote from: CatalinaWOW on July 23, 2024, 04:27:41 pmStorage can also be defined as season dependant imports. But there is a cost optimum to be had between storing so energy can bought when the price is low versus paying a premium when buying energy on demand. In Europe countries typically buy natural gas all through the summer for use in the winter so demand, production & prices stay more or less constant.

author: zilp
author_rank: Frequent Contributor
timestamp: July 23, 2024, 04:57:01 pm
content: Quote from: CatalinaWOW on July 23, 2024, 04:27:41 pmIn other words: Your claim that where you live has no meaningful wind resource at any time of the year was bullshit.Or, if you were just being hyper literal: Yeah, sure, your house doesn't have any meaningful wind resource. But your house also doesn't have any meaningful coal, oil, gas, or nuclear resource, so what exactly was your point?Exploiting energy resources isn't free, and getting energy into a valley surounded by mountains isn't free either. Whether the cost is "significant" is completely uninteresting. The only thing that would be interesting would be if you could show that it is significantlymoreexpensive than some alternative.Quote from: CatalinaWOW on July 23, 2024, 04:27:41 pmI haven't waved away anything. You claimed that huge amounts of seasonal storage were needed. And seasonal storage means storage that is cycled yearly, i.e., storage for the half of the year where renewable generation is lacking. For Germany, the last study I read on the topic came to the conclusion that we'd need about two weeks of demand in storage capacity to maintain grid reliability. While that is a lot of energy, it is a long way from "a few months" or half a year. And also, it doesn't even becessarily need construction of new storage facilities, because we do already have huge caverns that are currently used for storing natural gas, which can be repurposed for hydrogen and/or synthetic methane. What is needed are electrolysis/synthesis plants.Does that require "sizeable investments"? Maybe? Depends on what you mean by "sizeable", I guess?But ... is there any solution that doesn't require sizeable investments, that you mention this?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 23, 2024, 06:55:12 pm
content: Okay. I will agree that neither of our arguments were meaningful until numbers are applied. I have done rough costing for my situation, based on me personally solving my problems. I can dig up the numbers but they aren't really relevant to the real question which is community wide or society wide implementations. I will assert that scale changes don't make the costs go away, though they can reduce the costs amortized over the population. The amount of reduction isn't easy to predict. Again everything is local.I am not one of those Luddites emotionally tied to fossil sources. I have installed solar at my home. I am adding storage (for reliability reasons, bridging grid failures, not solar availability). Those costs and experiences give me a gut response to what larger scale and different purpose applications will run into and I apologize for being more negative than some would like. Even once numbers are applied any reader will have to approach the results with caution. Anyone who has done this kind of work knows how easy it is for both proponents and opponents to "put a thumb on the scale"

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2024, 07:13:29 am
content: Quote from: zilp on July 23, 2024, 04:57:01 pmI would tend to agree. The relevant term is Dunkelflaute, and while it is possible it lasts longer than two weeks (e.g.: three weeks), this would be an exceedingly rare condition.Seasonal storage is an interesting research subject and trying to solve that is not a bad idea, but it isn't strictly necessary. Storage in 12-24 hours, and on the other hand 1-3 week timescales is much more important. As always, it's about where to spend resources.For example, if 12-24hrs storage can be had by controlling existing HVAC and hot water + electric vehicle charging, it makes no sense to tackle the same storage with distributed li-ion batteries which cost at least 10 times more (and have significant environmental impact).And, if 3 week timescale can be had by building e.g. more pumped hydro, thermal storages for heating needs (e.g. operating at 75% efficiency), and improving grid connections (so that it's possible to import from further away), it makes no sense to invest 10x more money to try to build a 12-month timescale hydrogen infrastructure (operating at 25% efficiency).Research projects are fine because we need to explore the unknowns.

author: zilp
author_rank: Frequent Contributor
timestamp: July 24, 2024, 11:04:49 am
content: Quote from: Siwastaja on July 24, 2024, 07:13:29 amAlso, in that exceedingly rare case, one potentially could still burn natural gas, if one has gas power plants for burning hydrogen or synthetic methane. Assuming the whole natural gas business hasn't become completely uneconomical by then.Quote from: Siwastaja on July 24, 2024, 07:13:29 amThough battery storage for daily cycles is already economically viable (batteries tend to have a limited wall clock time life, but if you cycle them daily, the cost per kWh discharged is not astronomical). And sodium batteries might help with the environmental impact. But load control certainly is the cheapest option, where possible, and more electric vehicles will also provide more capacity that can be load controlled, while also providing the demand that pays for building more generation capacity, which then automatically becomes "over provisioned" for the load that you can't shift around.Quote from: Siwastaja on July 24, 2024, 07:13:29 amHydrogen and stuff wouldn't be at 25% efficiency, though. I mean, from electricity to hydrogen and back, you might be in that ballpark, but one big load in such a situation presumably would be heating, and a heat pump would get it back to ~ 75%, too.Of course, 12-month scale storage still wouldn't make a whole lot of sense.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 24, 2024, 11:55:46 am
content: Quote from: zilp on July 24, 2024, 11:04:49 amFor a heat pump you need to first convert the hydrogen back to electricity. To use it directly for heating is by far the most stupid idea.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 25, 2024, 04:18:41 pm
content: Wow, thread still running, well done.As has been mentioned, the solar farms covering acres, how many inverters do they use? I can't really imagine one larger than, say, 100kW, but do they exist? What technology is used, are semiconductors that large, and switching time?In my books, came across synchronous converters, even 100 years ago these were many MW. They claim efficiencies more than 90% so are they a realistic alternative to solid state inverters? There is the reliability problem, but my observed reliability of inverter TIG/MIG welders and AC drives leaves a lot to be desired. A blow up every 200 hours isn't good, but if they were used more then perhaps damp doesn't kill them so quickly, my experience of Lithium battery chargers.Watching the sun moving across the fields, and if it was solar panels, not wheat, then I would imagine a serious increase/decrease in solar output as the sun sweeps across the panels, or are the panels divided up into many inverters to fix the problem?

author: uer166
author_rank: Super Contributor
timestamp: July 25, 2024, 07:12:27 pm
content: Quote from: woodchips on July 25, 2024, 04:18:41 pmWhat in the world does this have to do with solar/industrial battery inverters? The data is out there, why do people keep making shit up

author: zilp
author_rank: Frequent Contributor
timestamp: July 25, 2024, 08:01:10 pm
content: Quote from: uer166 on July 25, 2024, 07:12:27 pmBecause well-established, proven technology can not possibly actually work if it isn't deployed to destroy the world, that is why.We have HVDC transmission systems that manage to feed gigawatts of power from a DC source into the AC grid using solid state inverters, something that anyone around this forum can be expected to be aware of ... but surely, there must be some unsurmountable problem with feeding a few MW from a utility scale solar plant into the grid! Probably it's the same problem that causes us to tear down and rebuild those HVDC inverters every two years ... not.

author: jonpaul
author_rank: Super Contributor
timestamp: July 25, 2024, 10:13:42 pm
content: all utility grids ARE by def "synchronous"Any added power connection is first synchronized and after connected.An unsync source needs a converter to connect.See any text on basic power engineering and grid stability.Jon

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 26, 2024, 01:46:12 am
content: Hey Benz and Ford proved you can get from place to place in a gasoline powered car. Why are people suggesting that there might be problems when multiplying that demonstration by millions?There are so many of the "rolling coal" types throwing shade at green energy that proponents of green energy assume that any word of caution or possible problems. I personally am quite sure that there will be problems, often not because of the technology but because of stupidity, oversight and procrastination. And I am equally sure that there will be problems that surprise all of us. It seems unlikely that any of this will prevent implementation, but the will be hiccups. Some quite disturbing to those affected.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 26, 2024, 03:35:29 am
content: Quote from: woodchips on July 25, 2024, 04:18:41 pmI refer you to the HVDC interconnectors used in Japan to connect the Western Japan 60Hz grid to the Eastern Japan 50Hz grid. In the post-war rebuilding period, USA and Europe brought their own 60Hz and 50Hz equipment. The grid remains divided today.The grid interconnectors once used synchronous converters. Today they've been upgraded to semiconductors.Despite this, interconnector capacity is still inadequate to supply energy needs stemming from the loss of Fukushima. The effect is that Eastern Japan is rationing power, whilst Western Japan has an energy surplus. Total interconnnector capacity is 1.2GW.

author: zilp
author_rank: Frequent Contributor
timestamp: July 26, 2024, 08:05:49 am
content: Quote from: CatalinaWOW on July 26, 2024, 01:46:12 amThe problem with this analogy is that we are already at the stage that multi-MW diesel engines are driving large ships, millions of gasoline powered cars are on the streets, and the suggested problem is "I doubt that diesel driven locomotives can work, because my cheap gasoline-powered lawn mover keeps crapping out".There are literally millions of microinverters in operation (Germany alone has about 650000 officially registered "Balkonkraftwerk" installations, those are all microinverters, and there probably are quite a few who don't bother to register theirs), Germany alone has more than 15000 solar power plants with nominal net peak power of more than 500 kW, five of them with more than 100 MW, we have dozens of HVDC links on the planet that each feed GW of DC power into AC grids.Just yesterday around noon, here in Germany, we had about 43 GW of solar power feeding into the grid, plus 4 GW of wind and 3 GW of hydro, at a total load of about 59 GW.The problem is not that people are suggesting problems. There are very qualified people who are suggesting problems and who are advising governments on strategies to mitigate them or who are working on engineering solutions to them, and that is very valuable. But that doesn't mean that any suggestion of a possible problem by people who obviously haven't even bothered to get a clue as to roughly what the current state of the technology is is valuable. Nor does such behaviour suggest that they are actually genuinely concerned about real problems or about solving those real problems.Quote from: CatalinaWOW on July 26, 2024, 01:46:12 amThat certainly isn't true for me, and I don't think that it is true for many others either. I very much welcome suggestions of genuine potential problems that have so far been overlooked, because the best thing that can happen is that we are aware of those problem as early as possible, so we can mitigate them before we sink billions into stuff that doesn't work, or experience devastating problems because of a screwed up roll-out.I don't assume that "any word of caution" is disingenuous, but I do conclude just that when it is obvious that the person speaking hasn't put in even the minimum amount of effort to have even the slightest clue what the current state of affairs is, and are spouting theories about supposed problems that are so blatantly obvious that obviously those people who are building renewable energy systems (believe it or not, those people tend to be electrical engineers) have thought of them decades ago, and have long since developed and deployed solutions for them, when the technology that supposedly is likely to be so very unreliable is in reality already deployed in thousands or millions of commercial products/installations, ...Quote from: CatalinaWOW on July 26, 2024, 01:46:12 amIt's just that that's exactly the thing that we've been hearing from nay-sayers for decades, all while renewable energy here in Germany has climbed from a percent or two (hydro power) of the electricity supply to regularly 80% plus. Always, the next few percent would make the grid collapse. Always, the proposed technology was imposible to build for some made-up "fundamental reason". Always, something catastrophic was going to happen any time now.Politicians and utility companies over here even built a big-ish (3 MW) wind turbine back in the 80s with the explicit goal of demonstrating that it doesn't work. To quote fromWikipedia:QuoteNow, that project did indeed fail, for reasons. But also, the Danes at the same time were already successfully building similarly sized wind turbines. And nowadays, we obviously have 15 MW models working just fine. Even though that fundamentally can't actually work, I guess.And note how all of that happened with zero giant catastrophic events.Now, obviously, there have been problems along the way. Obviously, not every approach worked out. Obviously, there have been prototypes that were dead ends. Obviously, here and there, solar inverters or wind turbines went up in flames. Those things obviously have been learned from, resulting in a pretty mature technology by now.So, yeah, there have been hiccups, of course there have been hiccups. But nothing remotely on the scale of being a problem for grid reliability. And with the emphasis on "have been", because much of the hiccups that people imagine are going to come are already in the past. And also, rarely, if ever, were the doomsday scenarios painted by nay-sayers in any way useful for improving the technology. What was useful were people actually conducting studies. People actualy modeling grids with varying contributions from various energy sources. People doing the actual work that was necessary to figure out stable control schemes. Not people shouting over and over some variation of "control systems can be unstable if improperly constructed" ... like that's a thing that engineers aren't aware of.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 26, 2024, 03:07:56 pm
content: I will only say that large scale conventional grids had been operating for quite some time -- at the time of the famous Northeastern US power blackout. And a few subsequent ones, all of which occured after analysis of what went wrong and many proposed solutions implemented.None of this is intended to delay implementation of new energy sources. Just saying that it isn't free, and in some areas will be more costly and difficult than others. And I remain sure that there will be surprises. Things somewhat similar to the discovery that hydroelectric dams, even those with fish ladders are harmful to whole species. Or that the fluorocarbons carefully engineered to be harmless weren't completely harmless. Or (as the Benz and Ford analogy was meant to convey) that we could put enough exhaust products into the atmosphere to impact the climate. Of course when we come across these surprises we will come up with solutions.