Will AC power distribution become obsolete?

[johansen]

Until we have a HV DC link to another location, state, island, country, all the AC needs is be near perfectly synced which acts as the standard frequency for all grid tied inverters to sync to.

all that does is make the problem more global. it doesn't fix the problem.

HV DC links breaks grid tied frequency unless it's bidirectional.

Power in to the grid has to equal power out.

Do hvdc links have infinite capacitance?.

[Marco]

Also I don't understand why Marco is talking about the zero crossing.

My point is that when there is a phase/load mismatch, to which normally the rotating mass responds by changing it's frequency, there is generally no real sinking going on ... the average load across the cycle remains the same sign. So for PV especially, it can always regulate its average output back to stabilise the grid as if it has inertia. If it is already maxed out it can't regulate up to emulate inertia, but that's what batteries and fuel cells will be for going to net zero.

With inverters defacto the only limiting part is cycle averaged load, as long as it can modulate the average input power sufficiently it can emulate all the inertia you want. A Complete DC grid would be a lot simpler, but alas.

[gf]

Also I don't understand why Marco is talking about the zero crossing.

My point is that when there is a phase/load mismatch, to which normally the rotating mass responds by changing it's frequency, there is generally no real sinking going on ... the average load across the cycle remains the same sign. So for PV especially it, it can always regulate its average output back to stabilise the grid as if it has inertia. If it is already maxed out it can't regulate up to emulate inertia, but that's what batteries and fuel cells will be for going to net zero.

With inverters defacto the only limiting part is cycle averaged load, as long as it can modulate the average input power sufficiently it can emulate all the inertia you want. A Complete DC grid would be a lot simpler, but alas.

And besides that, in order to "generate" reactive power, the inverter must be able to sink power for a duration of 10ms, storing the energy in the DC link capacitor, and feed the power back to the grid during the next 10ms.

[Marco]

Which represents significantly less energy than inverter capacitors absorb/release to deal with 50/60Hz in the first place each cycle.

The link Google provided me before calls these kind inverters with bidirectional capacity "multi-functional grid-connected inverters".

[johansen]

After thinking about this some more, power factor isnt the problem.

You cannot increase or decrease the frequency of the system with inductors or capacitors, the solar farms do not have the capacity to steer the grid via power factor.

Power factor affects the excitetion of the synchronous generators, but that is under control of the grid operator. When excition is decreased or increased but mechanical power into the generator is constant, the only change in power that you get is due to the rotor accelerating to a new angular position relative to the grid frequency. Or you get a change in power due to the voltage rising or falling, but this is muted by the tap changers down stream.
I have heard that grid operators typically run the generators at 90% lagging pf, because off setting some of the rotor exiction current with more current in the stator (with external capacitors) is cheaper than full excition. (This may be the case at 70% full load)

 Power factor also affects the voltage at the end of a long transmission line, but that is also under control.

A 100% solar farm can only decrease the frequency of the grid by reducing its power output, as it has no capacity to increase its output.

I still think such an algorithm i previously described will help a lot, and it could be implemented without the utilities knowledge.simply install a 3 second time constant and the solar output is proportional to the inverse increase of frequency with time, if the grid rises at a rate of .1 hz per 5 seconds then the power would ramp down at 10% per second, then back up over 10 seconds.

In conjunction with local batteries which could sink power

[IanB]

This gets back to a point I was trying to make earlier in the thread, which is the role of the grid operator in regulating the system.

If you have a multitude of smaller suppliers feeding power into the grid, it seems they cannot be left to individually decide what to do.

The grid operator has to look at supply and demand overall, and then somehow coordinate generation to match.

For instance, if we imagine a future where the grid demand is hypothetically 1000 MW, and this is being supplied by 100 renewable supplies of 10 MW each, and perhaps demand decreases by 50 MW. To keep things balanced, the grid operator has to tell an appropriate number of those suppliers to reduce their output by an appropriate amount, perhaps according to contractual arrangements of priority, or perhaps equally shared.

In an extreme case where there are tens, or hundreds of thousands of home solar installations dumping their excess power into the grid, how is that to be controlled?

[BrianHG]

I though I once read that the grid was beginning to use  GPS in North America to sync it's phase.

[Someone]

A 100% solar farm can only decrease the frequency of the grid by reducing its power output, as it has no capacity to increase its output.

A solar generator would have to operate below its available output to offer FCAS, just as any type of plant has to. This is not special to solar/wind/hydro/coal/gas/nuclear/distillate/chaff/etc. The advantage of DC links and inverters is they can respond faster.

[Someone]

The grid operator has to look at supply and demand overall, and then somehow coordinate generation to match.

For instance, if we imagine a future where the grid demand is hypothetically 1000 MW, and this is being supplied by 100 renewable supplies of 10 MW each, and perhaps demand decreases by 50 MW. To keep things balanced, the grid operator has to tell an appropriate number of those suppliers to reduce their output by an appropriate amount, perhaps according to contractual arrangements of priority, or perhaps equally shared.

In an extreme case where there are tens, or hundreds of thousands of home solar installations dumping their excess power into the grid, how is that to be controlled?

The grid is almost entirely distributed control already, generators will produce more/less power in response to change in frequency, and are programmed locally to adjust setpoint/output depending on the absolute frequency.

Dispatch/centralised control is slow, minutes and longer.

Existing residential solar inverters blindly add power to the grid up to some cutout (voltage and frequency) being distributed in small units and noisy that means they don't cause sudden co-ordinated changes. That is what the grid operators asked for, but it doesnt mean they cannot be more intelligent and provide inertia or smoother/more intelligent responses.

[johansen]

If you have a multitude of smaller suppliers feeding power into the grid, it seems they cannot be left to individually decide what to do.

They can, reduce power when frequency rises above 60hz, amd increase power below 60hz.

The problem is then, you cant control who is providing the power, thus you cant control who gets paid...

He who cuts production first loses money first...

[Connecteur]

Somewhere along the way, we got convinced that buying power from a monopoly was better than producing our own or forming cooperatives to generate it for the members. 

How much you wanna bet that creating an energy cooperative will be illegal?

[johansen]

Somewhere along the way, we got convinced that buying power from a monopoly was better than producing our own or forming cooperatives to generate it for the members. 

How much you wanna bet that creating an energy cooperative will be illegal?

Crane550 runs a 1 or 2MW local power grid in canada.

I dont know the details. But its not illegal or anything, ita just that large corporations with federal subsidies paid for the infrastructure long ago with other peoples money. You are free to buy it out. -it just costs a lot more the second time around because you have to pay for the inflationary theft plus the unforseen maintenance costs.

You cant even string fiber on a powerline in a public right of way for less than 4$ a foot in my county ..and that price is probably justified in the future cost of maintaining the poles.

[TimFox]

Somewhere along the way, we got convinced that buying power from a monopoly was better than producing our own or forming cooperatives to generate it for the members. 

How much you wanna bet that creating an energy cooperative will be illegal?

You don't specify your country of residence.
In the US, see  https://www.electric.coop/electric-cooperative-fact-sheet

[IanB]

The grid is almost entirely distributed control already, generators will produce more/less power in response to change in frequency, and are programmed locally to adjust setpoint/output depending on the absolute frequency.

You are not addressing the problem of interacting controllers. If every generator acts independently to respond to a change in frequency, then there will be a tendency to instability with multiple actors trying to control the same thing at the same time. Only if all the actors act in unison, by means of communication and centralized control action will the result be effective. You have never said how all the generators are linked and communicating with each other to produce the desired outcome.

[Andy Chee]

are programmed locally to adjust setpoint/output depending on the absolute frequency.

Wrong.

All generators in AEMO (eastern Australian power grid) must synchronise to the master frequency reference, Snowy Mountain hydro.

[Someone]

are programmed locally to adjust setpoint/output depending on the absolute frequency.

Wrong.

All generators in AEMO (eastern Australian power grid) must synchronise to the master frequency reference, Snowy Mountain hydro.

So there is zero FCAS? No generators are allowed to change their power delivery regardless of frequency? Equally stupid extreme of all or nothing. The basics of a stable grid is using the frequency to indicate supply/demand balance and allowing generators to respond to that signalling. Some plants do this more granularly/smoothy than others, some just wait for some extreme case and cut out.

... oh found it:
AEMO publication:
https://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Security-and-reliability/-/media/80004354B88B4FEF96EAB673DDC99820.ashx

Although any technology can participate in the FCAS market if technically capable, these services have generally been provided by thermal (such as coal and gas) and hydro generation.

So hydro is specifically used for FCAS and will push/pull frequency between dispatch periods.

Lets go another layer:
https://aemo.com.au/-/media/files/electricity/nem/security_and_reliability/ancillary_services/2024/market-ancillary-services-specification---v82-effective-3-june-2024.pdf?la=en

During enablement, an FCAS Facility must respond to Local Frequency without further
instruction from AEMO.

6.2.2. Control System Requirements
(a) Whenever Contingency FCAS is enabled, the FCAS Facility used to deliver the requested
Contingency FCAS must have a control system to automatically initiate:
(i) a Raise Response when Local Frequency exceeds the FCAS Facility’s Frequency
Deadband, which for a Variable Controller must not be less than the lower limit of
Market ancillary service specification
AEMO | Doc Ref: ESOPP_12 | 3 June 2024 Page 22 of 41
the NOFB and for a Switching Controller, must be equal to the Frequency
Deviation Setting; and
(ii) a Lower Response when Local Frequency exceeds the FCAS Facility’s Frequency
Deadband, which for a Variable Controller must not be greater than the upper limit
of the NOFB and for a Switching Controller, must be equal to the Frequency
Deviation Setting.
(b) The control system may be either a Variable Controller or a Switching Controller, or a
discrete combination of both, and must operate so that the Raise Response or Lower
Response is:
(i) for a Variable Controller, an amount commensurate with the difference between
Local Frequency and Frequency Deadband where the Local Frequency is between
the Frequency Deadband and the lower limit of the OFTB (for a Raise Response)
or upper limit of the OFTB (for a Lower Response) in accordance with the FCAS
Facility’s proportional response function10;
(ii) for a Switching Controller, one or more step changes if Local Frequency falls
below its Frequency Deviation Setting (for a Raise Response) or exceeds its
Frequency Deviation Setting (for a Lower Response); or
(iii) for a discrete combination of both, responses in accordance with sub-paragraphs
(i) and (ii).
(c) Where a Switching Controller is used, it must be capable of adjusting its Frequency
Deviation Setting to the Frequency Setting provided by AEMO with an Intrinsic
Uncertainty of <0.05 Hz for absolute Frequency Deviation Settings.

So yeah, thats power stations varying their output:
a) in response to absolute frequency
b) explicitly without global co-ordination

[Someone]

The grid is almost entirely distributed control already, generators will produce more/less power in response to change in frequency, and are programmed locally to adjust setpoint/output depending on the absolute frequency.

You are not addressing the problem of interacting controllers. If every generator acts independently to respond to a change in frequency, then there will be a tendency to instability with multiple actors trying to control the same thing at the same time. Only if all the actors act in unison, by means of communication and centralized control action will the result be effective. You have never said how all the generators are linked and communicating with each other to produce the desired outcome.

Yes it's a matter of control theory and keeping all the interactions stable, which is currently relying on frequency inertia to keep it stable (among other things).

It doesnt need an overlaid control signal to be stable, which is what you keep insisting is 100% necessary. How on earth did a bunch of coal and hydro plants balance power in the 1920's/1930's ? Frequency control. Same as we do today.

[IanB]

It doesnt need an overlaid control signal to be stable, which is what you keep insisting is 100% necessary. How on earth did a bunch of coal and hydro plants balance power in the 1920's/1930's ? Frequency control. Same as we do today.

Inertia is the key point. It can be provided by large base load alternators, or by large battery storage systems. Historically, the large centralized generators have provided that inertia. If you take them away, a control problem results.

[Someone]

It doesnt need an overlaid control signal to be stable, which is what you keep insisting is 100% necessary. How on earth did a bunch of coal and hydro plants balance power in the 1920's/1930's ? Frequency control. Same as we do today.

Inertia is the key point. It can be provided by large base load alternators, or by large battery storage systems. Historically, the large centralized generators have provided that inertia. If you take them away, a control problem results.

It can be provided by all sorts of sources, standalone flywheels, or as keeps being pointed out... DC grid inverters. Yes if the grid is to continue to use its current control scheme then the frequency inertia will need to be maintained, but that is perfectly capable of being provided with wind/solar powered inverters.

[IanB]

It can be provided by all sorts of sources, standalone flywheels, or as keeps being pointed out... DC grid inverters. Yes if the grid is to continue to use its current control scheme then the frequency inertia will need to be maintained, but that is perfectly capable of being provided with wind/solar powered inverters.

As other people in this thread are also pointing out, that is not true.

Inertia is a physical phenomenon. It can only provided by a physical systems that store energy, such as large rotating masses, or large battery banks. Wind and solar powered inverters do not store energy, so they cannot provide inertia in and of themselves.

If you want to emulate physical inertia, you have to connect all the little wind and solar sources distributed around the grid to a central control system, and make them act in concert with each other. You need a communication grid and central control.

[Someone]

It can be provided by all sorts of sources, standalone flywheels, or as keeps being pointed out... DC grid inverters. Yes if the grid is to continue to use its current control scheme then the frequency inertia will need to be maintained, but that is perfectly capable of being provided with wind/solar powered inverters.

As other people in this thread are also pointing out, that is not true.

Inertia is a physical phenomenon. It can only provided by a physical systems that store energy, such as large rotating masses, or large battery banks. Wind and solar powered inverters do not store energy, so they cannot provide inertia in and of themselves.

If you want to emulate physical inertia, you have to connect all the little wind and solar sources distributed around the grid to a central control system, and make them act in concert with each other. You need a communication grid and central control.

Inertia of the grid frequency does not require energy storage. Simply being able to regulate a plant's power output up and down provides frequency inertia.

Grid connected inverters do one better in that they can also bi-directionally move power and store energy on the DC side. Thats how inertia and FCAS is already provided by grid connected batteries.

As above all this occurs without centralised control, 100 small flywheels can produce the same result as 1 big flywheel. Ability to produce grid inertia (which inverters can provide) is the only important fact, that can be scaled to the required amount.

Since you seem to need some learning, how about doing the absolute minimum and reading wikipedia on the topic?
https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load

Flywheel physics does not apply to inverter-connected solar farms or other DC-linked power supplies. However, such power plants or storage systems can be programmed to follow the frequency signal.

https://en.wikipedia.org/wiki/Automatic_generation_control

[Someone]

Additional reading:
https://www.energy-storage.news/grid-inertia-measurement-trial-at-australias-biggest-battery-storage-project/
Work is underway to measure the actual inertia present on the Australian grid.

But brings the goods about as plainly as possible:

Inverter-based energy technologies like solar PV and wind can provide so-called ‘synthetic inertia’ or ‘virtual inertia’ to the grid: instead of the inertia coming physically from the large rotating mass of synchronous generators at thermal power plants, it can be delivered through inverters.

[IanB]

Since you seem to need some learning, how about doing the absolute minimum and reading wikipedia on the topic?
https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load

Flywheel physics does not apply to inverter-connected solar farms or other DC-linked power supplies. However, such power plants or storage systems can be programmed to follow the frequency signal.

https://en.wikipedia.org/wiki/Automatic_generation_control

That Wikipedia article simply repeats what I have been saying all along in this thread. Namely that stable frequency control comes from all the grid tied inverters being connected together and following a common  frequency signal so that they act in unison. It's even the very first sentence:

Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network.

If they are doing this, then they will tend to provide synthetic inertia, since they are all linked together and behaving like one big generator instead of lots of small generators.

Note what I said in an earlier post:

If you want to emulate physical inertia, you have to connect all the little wind and solar sources distributed around the grid to a central control system, and make them act in concert with each other. You need a communication grid and central control.

[Someone]

Since you seem to need some learning, how about doing the absolute minimum and reading wikipedia on the topic?
https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load

Flywheel physics does not apply to inverter-connected solar farms or other DC-linked power supplies. However, such power plants or storage systems can be programmed to follow the frequency signal.

https://en.wikipedia.org/wiki/Automatic_generation_control

That Wikipedia article simply repeats what I have been saying all along in this thread. Namely that stable frequency control comes from all the grid tied inverters being connected together and following a common  frequency signal so that they act in unison. It's even the very first sentence:

Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network.

Which is consistent with what I have been saying all along. There is no additional control/command/centralised decision making required, this can be done de-centralised/distributed. You have insisted there must be some system other than the grid to do this:

If they are doing this, then they will tend to provide synthetic inertia, since they are all linked together and behaving like one big generator instead of lots of small generators.

Note what I said in an earlier post:

If you want to emulate physical inertia, you have to connect all the little wind and solar sources distributed around the grid to a central control system, and make them act in concert with each other. You need a communication grid and central control.

that quoted point is incorrect. You are quoting yourself saying "you have to [use] a central control system". But you are now changing track and saying aggregation and distrubted control is a-ok and completely fine? I have put the point plainly several times and you disagreed:

The grid is almost entirely distributed control already, generators will produce more/less power in response to change in frequency, and are programmed locally to adjust setpoint/output depending on the absolute frequency.

You are not addressing the problem of interacting controllers. If every generator acts independently to respond to a change in frequency, then there will be a tendency to instability with multiple actors trying to control the same thing at the same time. Only if all the actors act in unison, by means of communication and centralized control action will the result be effective. You have never said how all the generators are linked and communicating with each other to produce the desired outcome.

Yes it's a matter of control theory and keeping all the interactions stable, which is currently relying on frequency inertia to keep it stable (among other things).

It doesnt need an overlaid control signal to be stable, which is what you keep insisting is 100% necessary. How on earth did a bunch of coal and hydro plants balance power in the 1920's/1930's ? Frequency control. Same as we do today.

I have restated the framing clearly and consistently maintained:
a) gird stability needs some quantity of frequency inertia
b) frequency inertia can be provided by a range of sources be they synchronous machines with inertia, or inverter systems
c) co-ordination of supply/demand balance is (already) provided through distributed control by measuring/signalling frequency of the grid

All have references above. AEMO explicitly requires distributed control, so it is not just practical but currently required/mandated to participate in the FCAS market (which is where the emerging inertia market is coming out of).

So what are you disagreeing with? Or is this some new way of "winning" by again claiming I'm saying something I have never said?

[IanB]

Distributed control means by definition that there is a central coordinator that distributes its control actions across the system.

This is why you have the reference to co-ordination used by the Wiki article, and by yourself.

You cannot use the word co-ordination and then imply that everything acts independently without reference to some central or out-of-band (Wikipedia words) signal.

It's a plain fact. If you have lots of individual generators all acting independently without reference to the other actors, you will not have frequency control, and you will not have grid stability.