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129MWhr Battery Doing its Job Down Under.

Zoomup
Impressive so far,

https://www.dailymail.co.uk/sciencetech/article-8082841/Elon-Musks-Tesla-battery-farm-saved-South-Australia-116-MILLION.html


Z.
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    Alan Capon:




    Zoomup:

    "Operating via the Hornsdale Power Reserve, it has helped to restore stability to the network . . . 




    It does not, and never will. A battery would normally be connected by a static inverter. As such, the connection provides no inertia and will not improve the stability of the system. In fact, by displacing conventional rotating plant, it may make it worse. 


    Regards,


    Alan. 


     




     

    Why do you need inertia when you have a power station with a response time of 100 milliseconds?


    This isn't some diesel generator that has to crank into life when it's needed.  It's a 129MWh battery connected to a 100MW inverter than can go from standby to full power before you have even realised that you have a supply problem.
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    One of the main issues here is overload, be it transient due to a fault on the transmission system or the trip of one or more generating sets. With rotating plant, the rotating mass has inertia, and will not instantly slow down when you overload it. It will supply a significant overload as it slows. An inverter however will be sized for its rated output and be very poor at trying to provide more than 100% of its rating. The net effect is that the system frequency will fall rapidly, and lead to the sort of issues we had last August. The system stability figure gives you the time (usually measured in seconds) that you have to resolve the issue by either adding generation or reducing load. Often load is shed, as that provides the fastest correction to balance load with generation. In terms of the battery, if it was supplying 50% load, or even charging, it could fairly quickly ramp up to 100% load. If it had been supplying 100% load, then it is unlikely there would be any more to be had. 


    Regards,


    Alan.
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    davezawadi:

    No Z  it is nothing like that simple. Let us look at this properly, using your car as an example. You are happily driving along a flat road at a constant speed and you come to a hill. More power is now needed from the engine to keep up the speed. Your engine however cannot speed up instantly because it's fuel supply is limited. To instantly change RPM takes infinite power, so it takes several seconds, as you do when you push the accelerator, to speed up. This is exactly the same as the grid, which has limited transient power available. It is true that a battery system could pretty much instantly add this power but it needs to know when to do it and how much which it gets from the frequency  change. If the frequency didn't change the battery would not supply extra power..... That is how control systems work, they need an error signal to respond.




    The Tesla Australian battery system can respond in a cycle or two as it is virtually instantaneous in operation when required to act. It has electronic controls so is very fast to detect and respond. No accelerators or mechanical regulators involved at all. The solution is not to load the generating system fully, allow some reserve power for short duration high demand. Or, have a very accurate independent master clock system that all generators synchronise to. 


    What type of system is used nowadays to synchronise generators? A monitor and respond type of system that can go wobbly if the frequency varies rapidly and never stabilises, trying to play catch up?


    Z.

  • 0

    Zoomup:

    . . . The solution is not to load the generating system fully, allow some reserve power for short duration high demand. . . 




    Ok, that could work. How many battery systems are you going to need to have doing nothing, to replace a conventional power station of 2000MW? Remember you need to account for changes in system load, generators dropping off the bars, as well as phase-to-phase and phase-to-earth faults on the power system. Is this as cost effective as running a conventional power station? 


    Regards,


    Alan. 

  • 0

    but unlike Dinorwig it will do nothing for the stability of the system as it has no inertia.



    I guess that depends on what you mean by grid stability. Maybe I'm getting confused by the specialised meaning of words, but I would have guessed that for a grid to be stable then supply needs to match demand (or vice versa) not only on a second-by-second basis but on a minute-by-minute and hour-by-hour basis too.  Rotational inertia is great for matching second-by-second (or faster) changes - but I'd guess is less useful much beyond that as they'll soon start slowing down and bring the grid frequency down with it. For hour-by-hour you can startup or shutdown generators - so no major problems there (providing you have enough spare capacity). The minute-by-minute changes are trickier I would have thought - traditionally requiring 'spinning reserve' - i.e. plants running and consuming fuel, but just at a tick-over rate and not producing any significant power - on the basis it's far quicker to increase the power of a running plant than start one up from stationary.


    From what I can gather, the Australian system has a lot of coal fired generation (about 75%) so probably not short of inertia - but likely poor response time for reasonably rapid changes in demand (or sudden loss of generation). So it seemed the Australians were using a lot of gas and diesel as something like spinning reserves - which proved rather expensive. It sounds like they're using the Tesla system to fill these minute-by-minute gaps until the coal stations can respond - seemingly saving a reasonable amount of money in the process.


    As an aside I wonder how much inertia we really need. Some small off-grid systems seem to be entirely inverter driven and seem to cope with (as a percentage of their output) very significant and rapid changes in load without major issues - indeed inverter generators seem to be sold a proving better stability than their purely mechanical counterparts. I guess issues aren't quite the same - a small system 'dropping' significantly while a fault cleared probably has a lot less impact than if an entire national grid did the same, but perhaps there may be ways of managing that sort of thing if we had to.


       - Andy.
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    Interesting technical discussion, but I fear that it misses the point. Everything has to be renewable innit?
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    This solar/battery system in central Australia didn't do quite so well:


    "Telstra struggling with overcast conditions, flooding, to keep solar-powered network up"

    https://www.abc.net.au/news/2020-03-07/towns-with-no-phone-coverage-when-it-is-cloudy/12033916


    Best regards


    Roger

  • 0

    Roger Bryant:

    This solar/battery system in central Australia didn't do quite so well:


    "Telstra struggling with overcast conditions, flooding, to keep solar-powered network up"

    https://www.abc.net.au/news/2020-03-07/towns-with-no-phone-coverage-when-it-is-cloudy/12033916


    Best regards


    Roger

     




    "Telstra says the stations that provide landline and mobile phone coverage to some remote communities in Central Australia are not robust enough to withstand several days of cloud cover."


    Your report seems to be dealing with telecommunications and not mains' power transmission.


    Z.

  • 0

    AJJewsbury:

    . . . I guess that depends on what you mean by grid stability. . . 




    Ok, by “stability”, I am meaning that if you have a short circuit, loss of load, or loss of generation, how long does the grid remain stable without collapsing / shedding customers. This is usually measured in seconds, and can range from a second or less for small systems to tens of seconds for a large power system. This “inertia” buys the power system operators time to correct the initial fault that has upset the balance between load and generation. 


    As an example, last August’s partial UK blackout was an example of what happens when there is insufficient inertia to allow the system to be rebalanced. The cost of having that inertia available from conventional rotating plant is another issue. What effectively happened is that automatic systems took over to shed load and rebalance the system, albeit with a number of customers temporarily disconnected. It did however do its job, as the vast majority of the power system remained operational and supplying customers. 


    Regards,


    Alan. 

  • 0

    Ok, by “stability”, I am meaning that if you have a short circuit, loss of load, or loss of generation, how long does the grid remain stable without collapsing / shedding customers. This is usually measured in seconds, and can range from a second or less for small systems to tens of seconds for a large power system. This “inertia” buys the power system operators time to correct the initial fault that has upset the balance between load and generation. 



    Thanks - I think I understand now.


    So if the system has only a small amount of inertia, would the battery system cutting in quickly - either supplying more power or absorbing extra power - likely help to extend the period available to adjust conventional generation? Presumably the less the difference between generated and consumed power the longer the spinning bits will remain within an acceptable speed/frequency.


       - Andy.

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