1 minute ago, studiot said:

I take your word for the 20% - 50 % spare capacity, as i said you are in a position to have better figures than I.

Did you take my point about hot standby requirement? Yes or no.

Just now, sethoflagos said:

This was never in dispute. I presume you read the bit about London being powered from South Wales during the blitz? Necessary at the time no doubt, but it is generally most economic to keep short distances between generation and demand centres.

But there are (were) also arguments for placing the generating capacity near to coalfields, hence the Trent, Soar and Ouse (including Drax).

The Wiki article also implicitly confirms my comment about fragmentation.

And today we see flood warning is certain areas coupled with drought orders in others because the once unified water industry is now in the same boat fragmented and worse because we are without a national water grid.

Edited June 12, 2025Jun 12 by studiot
spelling

9 minutes ago, studiot said:

Heathrow excepted ?

Just level it and construct a 15 GW nuclear station on the site. God would smile.

Just now, sethoflagos said:

Did you take my point about hot standby requirement? Yes or no.

I know what hot standby means, AGCR edit (I mean gas fired sorry) stations are the fastest fossil fuel stations for this.

But battery based supply a la Shetland is even faster.

Just now, sethoflagos said:

Just level it and construct a 15 GW nuclear station on the site. God would smile.

The staines gravel is already pretty level.

I do remember a proposal to move London airport to a more suitable site, with a proper transport link, on derelict land.

Heathrow would have then been sold off and the state could have made a massive profit from the real estate value of the site, in the midst of London.

Edited June 12, 2025Jun 12 by studiot

2 minutes ago, studiot said:

I know what hot standby means, AGCR stations are the fastest fossil fuel stations for this.

Advanced Gas-Cooled Reactor?! Perhaps you meant CCGT station? I know. Sutton Bridge was one of mine. A little before ENRON hit the headlines for all the wrong reasons.

Just now, sethoflagos said:

Advanced Gas-Cooled Reactor?! Perhaps you meant CCGT station? I know. Sutton Bridge was one of mine. A little before ENRON hit the headlines for all the wrong reasons.

Yes my bad.

I cross posted with my edit when I realised.

On 6/13/2025 at 12:05 AM, studiot said:

But battery based supply a la Shetland is even faster.

Now that the tone of the discussion has calmed a little, I recommend reading this paper: The future of frequency response in Great Britain

It's quite short and not too technical, and deals with the critical consideration of grid stability.

The meat of the analysis is in this paragraph:

3.1. GB grid model

The GB grid model used in this study is based on the swing equation:

df∕dt=f_n2(R+I−kD_nΔf)∕2E_nf.

f_n [Hz] is the nominal frequency of the grid and Δ f=f−f _n. E_n [MW.s] is the total rotational kinetic energy stored in the grid at f_n, which is what we define as inertia in this paper. R [MW] is the FR of the grid, which can be positive or negative. I [MW] is the power imbalance of the grid and is positive when generation is greater than demand and negative when demand is greater than generation. D_n[MW] is the demand of the grid at f_n and k is the demand damping constant, set to 0.02 in this paper.

To be clear, R here represents staged interventions by the grid to maintain frequency within statutary limits in response to imbalances, I, between generation and demand.

In my day, 20% of UK average load was met by three stations (Ferrybridge, Eggborough, and Drax) strung out along just 15 miles of the Aire Valley at the heart of the grid. 14 turboalternators churning out 8 GW This centre was bolstered by a similar capacity generated by a string of somewhat smaller stations (Rugeley, Drakelow, Castle Donington, Ratcliffe-on-Soar, High Marnham, Cottam, and West Burton) on the Trent Valley. Between them, their huge combined angular momentum provided the cental 'flywheel' of the system, to which all more remote generation units were forced (by physics) to follow in both frequency and phase. The resulting high value of E_n resulted in exceptionally low fluctuations of grid frequency, and consequently very rare need for direct intervention by the grid. Hence, the historically excellent stability and reliability of the UK grid.

As the paper referenced suggests, the transfer from coal to renewables will greatly reduce the rotational kinetic energy of grid supply. Essentially, it will become dominated by the considerably smaller nuclear component. And hence, if grid stability is to be maintained, there is going to be a far greater reliance on grid intervention, R. And key stages of this must activate within one second of notice. This is the real challenge to be faced by the transistion to renewables. Everything else is simple in comparison.

Edited June 14, 2025Jun 14 by sethoflagos
typo

This recent analysis suggests the RE switch can't come too soon.

https://www.theguardian.com/environment/2026/feb/05/flawed-economic-models-mean-climate-crisis-could-crash-global-economy-experts-warn

Flawed economic models mean the accelerating impact of the climate crisis could lead to a global financial crash, experts warn.

Recovery would be far harder than after the 2008 financial crash, they said, as “we can’t bail out the Earth like we did the banks”.

As the world speeds towards 2C of global heating, the risks of extreme weather disasters and climate tipping points are increasing fast. But current economic models used by governments and financial institutions entirely miss such shocks, the researchers said, instead forecasting that steady economic growth will be slowed only by gradually rising average temperatures. This is because the models assume the future will behave like the past, despite the burning of fossil fuels pushing the climate system into uncharted territory.

Tipping points, such as the collapse of critical Atlantic currents or the Greenland ice sheet, would have global consequences for society. Some are thought to be at, or very close to, their tipping points but the timing is difficult to predict. Combined extreme weather disasters could wipe out national economies, the researchers, from the University of Exeter and financial thinktank Carbon Tracker Initiative, said.

Their report concludes governments, regulators and financial managers must pay far more attention to these high impact but lower likelihood risks, because avoiding irreversible outcomes by cutting carbon emissions is far cheaper than trying to cope with them...

On 6/14/2025 at 2:40 AM, sethoflagos said:

Now that the tone of the discussion has calmed a little, I recommend reading this paper: The future of frequency response in Great Britain

It's quite short and not too technical, and deals with the critical consideration of grid stability.

The meat of the analysis is in this paragraph:

To be clear, R here represents staged interventions by the grid to maintain frequency within statutary limits in response to imbalances, I, between generation and demand.

In my day, 20% of UK average load was met by three stations (Ferrybridge, Eggborough, and Drax) strung out along just 15 miles of the Aire Valley at the heart of the grid. 14 turboalternators churning out 8 GW This centre was bolstered by a similar capacity generated by a string of somewhat smaller stations (Rugeley, Drakelow, Castle Donington, Ratcliffe-on-Soar, High Marnham, Cottam, and West Burton) on the Trent Valley. Between them, their huge combined angular momentum provided the cental 'flywheel' of the system, to which all more remote generation units were forced (by physics) to follow in both frequency and phase. The resulting high value of E_n resulted in exceptionally low fluctuations of grid frequency, and consequently very rare need for direct intervention by the grid. Hence, the historically excellent stability and reliability of the UK grid.

As the paper referenced suggests, the transfer from coal to renewables will greatly reduce the rotational kinetic energy of grid supply. Essentially, it will become dominated by the considerably smaller nuclear component. And hence, if grid stability is to be maintained, there is going to be a far greater reliance on grid intervention, R. And key stages of this must activate within one second of notice. This is the real challenge to be faced by the transistion to renewables. Everything else is simple in comparison.

I've only just read this. Would it be a silly idea to run a couple of vast flywheels, just to add "ballast" to the system? One could even simply retain a couple of these big turbo-alternator sets, unpowered, and spun up and maintained to 50Hz off the grid.

Edited February 5Feb 5 by exchemist

14 hours ago, exchemist said:

I've only just read this. Would it be a silly idea to run a couple of vast flywheels, just to add "ballast" to the system? One could even simply retain a couple of these big turbo-alternator sets, unpowered, and spun up and maintained to 50Hz off the grid.

I've had similar thoughts.

However, the units couldn't be 'unpowered' otherwise there would be no electrical coupling. What I'm not clear on is whether rotational KE on the demand side (power consuming units) is as useful as that of power generating units. Both tend to flatten the rate of frequency change, but act in opposite directions which might be an issue.

11 hours ago, sethoflagos said:

I've had similar thoughts.

However, the units couldn't be 'unpowered' otherwise there would be no electrical coupling. What I'm not clear on is whether rotational KE on the demand side (power consuming units) is as useful as that of power generating units. Both tend to flatten the rate of frequency change, but act in opposite directions which might be an issue.

... Not an issue apparently, see Flywheel Storage Power System

A flywheel-storage power system uses a flywheel for grid energy storage, (see Flywheel energy storage) and can be a comparatively small storage facility with a peak power of up to 20 MW. It typically is used to stabilize to some degree power grids, to help them stay on the grid frequency, and to serve as a short-term compensation storage. Unlike common storage power plants, such as the pumped storage power plants with capacities up to 1000 MWh, the benefits from flywheel storage power plants can be obtained with a facility in the range of a few kWh to several tens of MWh.[1] They are comparable in this application with battery storage power plants.

Reading between the lines, the limited current scale of such installations seems due to a lack of perceived urgency rather than any significant technological limit. And the UK always has Dinorwig - it would take one monster of a flywheel to compete with that.

17 minutes ago, sethoflagos said:

... Not an issue apparently, see Flywheel Storage Power System

Reading between the lines, the limited current scale of such installations seems due to a lack of perceived urgency rather than any significant technological limit. And the UK always has Dinorwig - it would take one monster of a flywheel to compete with that.

+1

Dinorwig is in Wales, the are are 6 more pumped storage schemes already working or just started in Scotland.

Pumped storage has another advantage over a flywheel. - Flywheels run down, the pumped water waits quietly untill you need to use it.

12 minutes ago, studiot said:

Pumped storage has another advantage over a flywheel. - Flywheels run down, the pumped water waits quietly untill you need to use it.

Swings and roundabouts. Flywheels lose ~4% a day, pumped hydro has a round trip efficiency of about 75%. No free lunches.

But flywheels don't directly yield electricity. Your pumped storage 75% is presumably electric pump to water storage and back to electricity.

3 hours ago, sethoflagos said:

Swings and roundabouts. Flywheels lose ~4% a day, pumped hydro has a round trip efficiency of about 75%. No free lunches.

In places like Southern California, pumped storage also loses some to evaporation while it sits. IIRC, there are ideas out there, like covering the reservoir with plastic balls, or other forms of coverage.

On 2/5/2026 at 8:21 PM, exchemist said:

I've only just read this. Would it be a silly idea to run a couple of vast flywheels, just to add "ballast" to the system? One could even simply retain a couple of these big turbo-alternator sets, unpowered, and spun up and maintained to 50Hz off the grid.

That sounds like a long established technology called Synchronous Condensers and Australia is currently adding them to cover the withdrawal of thermal (spinning) power plants. SynCons are expensive with a long lead time for manufacture and unlike batteries have limited ways to make revenue other than as system inertia and frequency control so there is incentive to perfect inverter controlled virtual inertia - which appears to primarily involve updated inverter software or possibly upgrading the inverters. Trust in virtual inertia is not all the way there; it is being used but it seems to still be on trial, to see how well they perform in the real world. We did discuss virtual inertia on another thread.

It is also possible to retrofit gas power plants (any thermal generator? Seimens do them I think) with clutches, to allow the generator to disconnect from the 'engine' (gas turbines usually) and remain online, providing spinning inertia like when in full operation, as the equivalent of a SynCon.

Edited February 7Feb 7 by Ken Fabian

8 hours ago, Ken Fabian said:

That sounds like a long established technology called Synchronous Condensers and Australia is currently adding them to cover the withdrawal of thermal (spinning) power plants.

Not quite the same thing, Ken.

Granted, much of the physical hardware is the same, but syncons are specifically designed for power factor correction, and therefore have excitation circuitry designed for the production of reactive power, either lead or lag, as an alternative to (typically) thyristor switched static VAR compensators (SVCs).

What they don't do is generate torque to any large degree and are thus unable (in standard form) to replace active power generation shortfalls beyond a few cycles.

The flywheel version provides the necessary large energy storage capacity to fulfill that role.

It's interesting to consider whether these various functionalities could be combined in a single machine, though I suspect that idea would run into significant degrees of freedom issues.

@sethoflagos My mistake, although they do share some characteristics. The larger Syncons are very massive, nearly as massive as dedicated flywheels, but yes, flywheels will do a different task and can be run down; Syncons look intended to maintain their rotation rate with enough inertia to limit the rate of loss or gain in speed from grid variability. Presumably they will consume power to keep that rotation rate close to steady?

Until confidence in synthetic inertia is established a hybrid of Syncons with batteries might be better than including flywheels.

17 hours ago, exchemist said:

I've only just read this. Would it be a silly idea to run a couple of vast flywheels, just to add "ballast" to the system? One could even simply retain a couple of these big turbo-alternator sets, unpowered, and spun up and maintained to 50Hz off the grid.

I am a fan of raising weights for potential energy. There are no storage losses and requires less space than water. Just wish I could find how it compares to other storage methods for energy loss during reuse.

7 hours ago, npts2020 said:

I am a fan of raising weights for potential energy. There are no storage losses and requires less space than water. Just wish I could find how it compares to other storage methods for energy loss during reuse.

I have never understood how this can work at scale. It seems to me the mass of such weights cannot remotely compare with the mass of water that can be given extra gravitational potential energy by a couple of reversible pump/turbines in the space of a few hours.

I think, though, I would expect the losses to be lower than with pumped storage, as there won't be losses to turbulence and "slippage" through the turbine. It will be just a matter of the efficiency of the electric motor/generator running in forward and reverse directions, which you also have in a pumped storage setup.

A few facts and figures for comparison.

It is interesting to Google" the world's largest flywheel."

Key Details on Largest Flywheels:

• Ireland (Largest Single Unit): Located at a former coal-fired plant, this 177-ton, 30 MW synchronous condenser is designed to provide inertia to the power grid, helping integrate renewable energy like wind. It takes 20 minutes to reach maximum speed and is housed in a vacuum to reduce resistance.

• China (Largest System): The Dinglun plant, completed in 2024, uses 120 units, each with high-speed magnetic bearings. It is capable of storing 30 MW of power, sufficient for grid-level frequency regulation.

• Previous Record Holder: Before the Dinglun project, a 20 MW flywheel facility in Stephentown, New York, was considered the largest. 

The main discriminator for the pumped/reservoir approach, as compared to the large flywheel approach, seems to be the efficiency of the pumps compared to the efficiency of the flywheel bearings. Those are the primary 'loss' mechanisms for either system.
Does anyone have relevant 'ballpark' figures, and how they scale ?
( personally, and without evidence, I favor the pumping/reservoir approach )

Edited February 8Feb 8 by MigL

5 hours ago, MigL said:

The main discriminator for the pumped/reservoir approach, as compared to the large flywheel approach, seems to be the efficiency of the pumps compared to the efficiency of the flywheel bearings. Those are the primary 'loss' mechanisms for either system.
Does anyone have relevant 'ballpark' figures, and how they scale ?
( personally, and without evidence, I favor the pumping/reservoir approach )

There’s still conversion from mechanical to/from electrical for a flywheel that represents a loss. That’s the comparison for pump efficiency.

The analogue of spin-down is the evaporation that was mentioned

1 hour ago, exchemist said:

I think, though, I would expect the losses to be lower than with pumped storage, as there won't be losses to turbulence and "slippage" through the turbine.

Don't forget that winching systems rely on belt friction for cables to grip pulleys etc. (capstan equation and all that good stuff), and high ratio gearboxes can have significant losses. I wouldn't contradict your expectation as such, but I'd prefer to check the data first. It may not be quite so clear cut.

Again... no free lunches.

Not to mention the capital costs involved...

(Apologies for delayed response - network went awol for 24 hrs)

23 hours ago, studiot said:

China (Largest System): The Dinglun plant, completed in 2024, uses 120 units, each with high-speed magnetic bearings. It is capable of storing 30 MW of power, sufficient for grid-level frequency regulation.

Does anyone actually understand this?

Is that 30MW for a millisecond or a millennium? Surely the unit of interest is Joules.

22 minutes ago, sethoflagos said:

Don't forget that winching systems rely on belt friction for cables to grip pulleys etc. (capstan equation and all that good stuff), and high ratio gearboxes can have significant losses. I wouldn't contradict your expectation as such, but I'd prefer to check the data first. It may not be quite so clear cut.

Again... no free lunches.

Not to mention the capital costs involved...

(Apologies for delayed response - network went awol for 24 hrs)

Good points. As I say, regardless of the comparative efficiencies I am sceptical about weights in old mine shafts etc., as I just don't see how enough weight can be shifted, compared to pumping water.