Will AC power distribution become obsolete?

[Marco]

Perhaps, but what is the "maximum output"? What if it is hundreds of megawatts? Can a software emulation source or sink that amount of power?

If you pay for it.

[David Hess]

But can a gyrator replace the inductor in a buck/boost converter?  This is essentially the energy storage analogy I was going for.

It can replace it in a functional sense in acting like an inductor, but the current has to come from another source so it is no more efficient than a resistor.  If the power amplifier was class-d, then a gyrator could simulate an inductor completely including energy storage, but then the inductance is part of the class-d amplifier.

Similarly, flywheels and/or turbines can provide grid inertia that inverters cannot supply.

Inverters *can* supply grid inertia if desired.  The difference is that mechanical storage through angular momentum can support a very high peak power so handles surges and overloads inherently well.  An inverter can be designed to do this also, but as considerable cost.

Doesn't Tesla's big power stabilization units do exactly this?

[David Hess]

Perhaps, but what is the "maximum output"? What if it is hundreds of megawatts? Can a software emulation source or sink that amount of power?

Power is only limited by the hardware.  The battery storage has a power limit, which if enough energy is stored can be ignored, and the inverters have their own power limit, which is extended by using more inverters in parallel.  There is no inherent limit from the software or control.

[IanB]

Perhaps, but what is the "maximum output"? What if it is hundreds of megawatts? Can a software emulation source or sink that amount of power?

Power is only limited by the hardware.  The battery storage has a power limit, which if enough energy is stored can be ignored, and the inverters have their own power limit, which is extended by using more inverters in parallel.  There is no inherent limit from the software or control.

Understood, but my question, rationally, is about practical limits, not theoretical limits. Turbine/generator sets provide grid stabilization at power levels of hundreds of megawatts, for free, because they are already there to generate power.

If you need to emulate a similar amount of inertia at the hundreds of megawatts level with battery storage and electronics capable of sourcing and sinking that amount of transient power, then it's not free anymore, because absent the grid stabilization requirement you wouldn't need that additional cost. And who pays for it? Is the wind/solar facility owner going to be required to pay for something that is a significant addition to their base equipment cost? Or is the grid operator going to have to pay for a thing they wouldn't ordinarily need to have?

[johansen]

The inertia of a generator is not free.

As the generator leads or lags, the current has to go up if real power stays constant.-which it by default does because real power feeding the generator stays as constant as the stream pressure at the turbine.


Now, regarding solar farms. If every grid tied inverter out there used a disciplined local oscillator with a 1 hour time constant, instead of simply following the grid every single half cycle, the grid would have 10 times as much inertia as it does now.

-they would also hold up the local power grid when the lines break . And that could get spicy

[IanB]

The inertia of a generator is not free.

As the generator leads or lags, the current has to go up if real power stays constant.-which it by default does because real power feeding the generator stays as constant as the stream pressure at the turbine.

By "not free", do you mean the cost of the generator is increased above the base cost if it has to provide grid stabilization in addition to the normal generation capacity? Because I was making the implicit assumption that a generator is big and has a lot of inertia by default, and engineers wouldn't add cost by making it bigger than it needs to be without a strong justification.

[David Hess]

Power is only limited by the hardware.  The battery storage has a power limit, which if enough energy is stored can be ignored, and the inverters have their own power limit, which is extended by using more inverters in parallel.  There is no inherent limit from the software or control.

Understood, but my question, rationally, is about practical limits, not theoretical limits. Turbine/generator sets provide grid stabilization at power levels of hundreds of megawatts, for free, because they are already there to generate power.

The practical limits just come down to the economics and politics.  See below about the later.  And batteries and inverters are decreasing in cost, while large polyphase alternators are an established technology and not getting less expensive.

If you need to emulate a similar amount of inertia at the hundreds of megawatts level with battery storage and electronics capable of sourcing and sinking that amount of transient power, then it's not free anymore, because absent the grid stabilization requirement you wouldn't need that additional cost. And who pays for it? Is the wind/solar facility owner going to be required to pay for something that is a significant addition to their base equipment cost? Or is the grid operator going to have to pay for a thing they wouldn't ordinarily need to have?

In theory people should be paying *now* for the inertia that the older mechanical systems connected to the AC power grid provide because that stability is required, just like they should be paying a premium for dispatchable power, which does not include solar or wind, because it is available at any time.  This premium comes from solar and wind *not* being able to provide baseload or dispatchable power, unless backed up with expensive battery and inverter systems.

In practice they are not required to, so solar and wind sources are receiving a subsidy by making dispatchable and baseload systems less economical to operate, even though they are required for grid stability.

[tooki]

While it could simplify things in homes and sync better with renewables, AC's widespread infrastructure and historical use still make it practical for now.

What exactly does it simplify? And in return it complicates many things.

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

[johansen]

The inertia of a generator is not free.

As the generator leads or lags, the current has to go up if real power stays constant.-which it by default does because real power feeding the generator stays as constant as the stream pressure at the turbine.

By "not free", do you mean the cost of the generator is increased above the base cost if it has to provide grid stabilization in addition to the normal generation capacity? Because I was making the implicit assumption that a generator is big and has a lot of inertia by default, and engineers wouldn't add cost by making it bigger than it needs to be without a strong justification.

The stabilizing effect of the inertia of the generator is simply that it takes energy to change its speed.

Synchronous condensers, which are just synchronous motors free wheeling, also add inertia to the grid. Induction motors do not, because they only dump power into the grid if the frequency falls below 59,58,57 hz faster than the load causes the induction motor to slow down.

So anyhow, if synchronous condensers add inertia, what makes you think they are free? They have static losses and when current (real or not) is drawn from them, due to frequenxy and voltage changes, do you not see there is i^2R losses?

The same for the generator.

Lets assume the grid has a 1 second time constant due to the inertia of the generators, which isnt very much. So say that inertia is equal to 62% of 1 second of total grid power consumption.

If solar makes up 10% of the grid, and provided power via a trained oscillator with a 1 minute time constant, the grid's inertia would be able to be increased by the energy stored in the capacitors of those inverters.

It does not mean the inverters are capable of dumping out all their energy quickly, but they dont need to. We are talking small, .95 leading or lagging power factor changes over the course of a few seconds. The contribution of losses due to the current rising from 100 to 102% is very small, but it is by no means free.

Now im not sure this would work without utility control over the inverters.

Because if you have the inverters always wanting to push the grid back to 60hz, the problem is the inverters dont know if they should export leading or lagging power to do so, unless they also were synchronized to a gps clock, and had knowledge of what the voltage should be.

[TimFox]

While it could simplify things in homes and sync better with renewables, AC's widespread infrastructure and historical use still make it practical for now.

What exactly does it simplify? And in return it complicates many things.

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

There used to be a distinction:  "generator" meant DC, while "alternator" meant AC.
I was a youth when US automobiles changed from generators to alternators, after solid-state rectification became practicable.
Like many other distinctions, the (d)evolution of language seems to have removed this distinction.

[jonovid]

No! because we do not have free worldwide gigawatt power VLF atmospheric waveguide broadcastinging.  Nikola Tesla did gave it a go.
also- increasing the distribution frequency beyond 100Hz would be interesting for electric power transmission transformer designs.

 

[johansen]

Read here
https://www.statkraft.co.uk/newsroom/2023/helping-the-uk-power-grid-spin-back-its-system-inertia

So it appears 900Mwatt seconds (i assume they mean 900Mega joules seconds) can be had from a 67Mwatt condenser and a 40 ton flywheel. This is 1% of what the uk needs to add.

[coppice]

There used to be a distinction:  "generator" meant DC, while "alternator" meant AC.
I was a youth when US automobiles changed from generators to alternators, after solid-state rectification became practicable.
Like many other distinctions, the (d)evolution of language seems to have removed this distinction.

I don't know about where you live, but in the UK that distinction only applied to cars. Apart from cars, alternator has always meant an AC generator, and generator has meant anything that generates.

[IanB]

There used to be a distinction:  "generator" meant DC, while "alternator" meant AC.
I was a youth when US automobiles changed from generators to alternators, after solid-state rectification became practicable.
Like many other distinctions, the (d)evolution of language seems to have removed this distinction.

There can be regional variations. For example, in the UK, a DC generator in a car was always known as a dynamo.

[Someone]

Understood, but my question, rationally, is about practical limits, not theoretical limits. Turbine/generator sets provide grid stabilization at power levels of hundreds of megawatts, for free, because they are already there to generate power.

If you need to emulate a similar amount of inertia at the hundreds of megawatts level with battery storage and electronics capable of sourcing and sinking that amount of transient power, then it's not free anymore, because absent the grid stabilization requirement you wouldn't need that additional cost. And who pays for it? Is the wind/solar facility owner going to be required to pay for something that is a significant addition to their base equipment cost? Or is the grid operator going to have to pay for a thing they wouldn't ordinarily need to have?

As above, pretty much every inverter is able to produce this. So we have at least whatever the installed capacity of inverters is (given lots of those are on variable/unreliable energy sources, there is already a multiplier above the load average).

The additional cost is practically nil as its almost entirely software that is in the way at the moment. You could increase the peak/surge capacity of the inverters and add some more bus capacitance if even more inertia is required above the current availability.

In theory people should be paying *now* for the inertia that the older mechanical systems connected to the AC power grid provide because that stability is required, just like they should be paying a premium for dispatchable power, which does not include solar or wind, because it is available at any time.  This premium comes from solar and wind *not* being able to provide baseload or dispatchable power, unless backed up with expensive battery and inverter systems.

In practice they are not required to, so solar and wind sources are receiving a subsidy by making dispatchable and baseload systems less economical to operate, even though they are required for grid stability.

Spinning generators are not required. Notably the Australian market does price stability and pay to operators who can provide it (be that flywheels or batteries) while at the same time prohibiting wind/solar from enabling that capability. Agree it should be part of the pricing/costing but that needs to be in a fair market where any technological solution that delivers the functionality/resource can participate equally.

[Someone]

Perhaps, but what is the "maximum output"? What if it is hundreds of megawatts? Can a software emulation source or sink that amount of power?

If you pay for it.

I think this is going off into the sort of silliness/disingenuous/sealioning that would produce the question:
"but a residential solar install is only 5kW, how could that deliver the xxGW the grid currently demands?"

[David Hess]

In theory people should be paying *now* for the inertia that the older mechanical systems connected to the AC power grid provide because that stability is required, just like they should be paying a premium for dispatchable power, which does not include solar or wind, because it is available at any time.  This premium comes from solar and wind *not* being able to provide baseload or dispatchable power, unless backed up with expensive battery and inverter systems.

In practice they are not required to, so solar and wind sources are receiving a subsidy by making dispatchable and baseload systems less economical to operate, even though they are required for grid stability.

Spinning generators are not required. Notably the Australian market does price stability and pay to operators who can provide it (be that flywheels or batteries) while at the same time prohibiting wind/solar from enabling that capability. Agree it should be part of the pricing/costing but that needs to be in a fair market where any technological solution that delivers the functionality/resource can participate equally.

That is right.  I argued earlier that inverters can be used to provide grid stability, but they must be designed that way.  A large battery bank with an inverter which can both source and sink power can provide grid stability up to its power limit, which is exactly what Australia has done.

Now contrast that with other areas that are installing solar and wind without installing additional grid stability and then must limit the contributions of solar and wind.  The cost of the inverters and batteries is considerable.

[Someone]

In theory people should be paying *now* for the inertia that the older mechanical systems connected to the AC power grid provide because that stability is required, just like they should be paying a premium for dispatchable power, which does not include solar or wind, because it is available at any time.  This premium comes from solar and wind *not* being able to provide baseload or dispatchable power, unless backed up with expensive battery and inverter systems.

In practice they are not required to, so solar and wind sources are receiving a subsidy by making dispatchable and baseload systems less economical to operate, even though they are required for grid stability.

Spinning generators are not required. Notably the Australian market does price stability and pay to operators who can provide it (be that flywheels or batteries) while at the same time prohibiting wind/solar from enabling that capability. Agree it should be part of the pricing/costing but that needs to be in a fair market where any technological solution that delivers the functionality/resource can participate equally.

That is right.  I argued earlier that inverters can be used to provide grid stability, but they must be designed that way.  A large battery bank with an inverter which can both source and sink power can provide grid stability up to its power limit, which is exactly what Australia has done.

Now contrast that with other areas that are installing solar and wind without installing additional grid stability and then must limit the contributions of solar and wind.  The cost of the inverters and batteries is considerable.

You've glossed right over the important bit....
solar and wind (where they use DC linked inverters) can provide inertia/frequency control using the inverter with some appropriate software.

As a specific example in Australia, there are wind farms that have this feature already in the controls but it is prohibited from being used at an administrative (albeit technically informed) level.

Wind and solar do not necessarily need additional inertia sources to be installed, they can provide it themselves if required. Without additional hardware.

[Marco]

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

Anything which can't be synchronously generated at 50/60 Hz might as well be DC, because it's a lot easier to get to DC than 50/60 Hz.

[nctnico]

In theory people should be paying *now* for the inertia that the older mechanical systems connected to the AC power grid provide because that stability is required, just like they should be paying a premium for dispatchable power, which does not include solar or wind, because it is available at any time.  This premium comes from solar and wind *not* being able to provide baseload or dispatchable power, unless backed up with expensive battery and inverter systems.

In practice they are not required to, so solar and wind sources are receiving a subsidy by making dispatchable and baseload systems less economical to operate, even though they are required for grid stability.

Spinning generators are not required. Notably the Australian market does price stability and pay to operators who can provide it (be that flywheels or batteries) while at the same time prohibiting wind/solar from enabling that capability. Agree it should be part of the pricing/costing but that needs to be in a fair market where any technological solution that delivers the functionality/resource can participate equally.

That is right.  I argued earlier that inverters can be used to provide grid stability, but they must be designed that way.  A large battery bank with an inverter which can both source and sink power can provide grid stability up to its power limit, which is exactly what Australia has done.

Now contrast that with other areas that are installing solar and wind without installing additional grid stability and then must limit the contributions of solar and wind.  The cost of the inverters and batteries is considerable.

You've glossed right over the important bit....
solar and wind (where they use DC linked inverters) can provide inertia/frequency control using the inverter with some appropriate software.

As a specific example in Australia, there are wind farms that have this feature already in the controls but it is prohibited from being used at an administrative (albeit technically informed) level.

Wind and solar do not necessarily need additional inertia sources to be installed, they can provide it themselves if required. Without additional hardware.

But not infinitely as the clocks in the small power sources will drift! At some point the small power sources will need to be re-synchronised to the large, synchronised power sources (= power plants). If the large power plants are no longer providing a low enough impedance to do this, there will have to be alternative ways to synchronise the grid. This is a basic clock synchronisation problem. And no, GPS is not suitable for this purpose as it is way too vulnerable / unreliable.

[paulca]

Now im not sure this would work without utility control over the inverters.

This, from memory, is one of the clauses in the new euro/uk solar grid connection requirements.   The G98/99/100 codes.

Grid tie inverters beyond a certain size (3.3kW IIRC) are required to respond to frequency and phase signalling.  So that during times of high sun and low local demand larger inverters can be signalled with a tiny phase shift from the grid operator, to "back down" and not keep pushing to max.

[tooki]

While it could simplify things in homes and sync better with renewables, AC's widespread infrastructure and historical use still make it practical for now.

What exactly does it simplify? And in return it complicates many things.

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

There used to be a distinction:  "generator" meant DC, while "alternator" meant AC.
I was a youth when US automobiles changed from generators to alternators, after solid-state rectification became practicable.
Like many other distinctions, the (d)evolution of language seems to have removed this distinction.

I don’t think that was ever the case.

If anything, the distinction was between dynamos (DC) and alternators (AC). “Generator” is the umbrella term that encompasses both of those.

[tooki]

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

Anything which can't be synchronously generated at 50/60 Hz might as well be DC, because it's a lot easier to get to DC than 50/60 Hz.

Sure. But what non-solar renewable can’t be generated synchronously? Maybe wind?

Hydro is certainly synchronous. Anything where we generate steam, synchronous.

[Marco]

But not infinitely as the clocks in the small power sources will drift! At some point the small power sources will need to be re-synchronised to the large, synchronised power sources (= power plants). If the large power plants are no longer providing a low enough impedance to do this, there will have to be alternative ways to synchronise the grid. This is a basic clock synchronisation problem. And no, GPS is not suitable for this purpose as it is way too vulnerable / unreliable.

At net zero the PV/battery/seasonal storage plants will be multi-GW, they will be large power plants. Though you can just use powerline comms too. If the power cable is down it don't matter.

[tautech]

The only renewable that is “natively” DC is solar. All the others involve a generator at some point, which can be either.

Anything which can't be synchronously generated at 50/60 Hz might as well be DC, because it's a lot easier to get to DC than 50/60 Hz.

Sure. But what non-solar renewable can’t be generated synchronously? Maybe wind?

Hydro is certainly synchronous. Anything where we generate steam, synchronous.

Grid tied inverters take care of this for us to match the base load generation frequency.