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Mains frequency

Kelly Marie Angel
Just checked the dynamic demand site and the frequency was down to around49.7 cycles almost down to the lower legal limit never seen that before
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    As I type this (10 40 AM ) a little over a third of our mains is now inverter derived, about 30% from wind, and 5% from undersea links - French nuclear probably, and if the gridwatch website is to be believed about 6% from solar.

    At the same time a lot of the spinning load  from large industrial plants, cooling systems and so forth is now more likely to be variable frequency drive than the plain induction motor that turns generator during a phase shift it would have been.

    I think it is quite credible that we have already lost half the inertia we had when the systems that control the grid were being designed, and the trend will continue - if we add a few GW of car charging load that will not be inertial either.

    The frequency shift thing has an elegant and fail -afe simplicity, in that the phase shifts automatically cause current to flow from places with an excess of generation towards those with more load, so maybe we should continue to emulate it with the larger inverters at least until a clear alternative is available. It also allows things like the dynamic demand circuit, perhaps optimized better, to give smart load shedding within the appliance without needing any network connection and all the time delay and unreliability that entails.
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    Denis McMahon:





    Posted by Simon Barker on Feb 14, 2020 8:13 am



    Or build big battery banks around the country.  Spare power from renewables can be stored.  Then when the generations drops too low, the batteries can top the grid up for long enough to bring backup generators on line.




    On a grid system powered by solar power we would certainly lose the stability provided by inertia. However, this is hypothetical, since I cannot envisage such systems. Solar panels are not very clever at night. Also bear in mind that nuclear power, though not strictly renewable, is virtually carbon free and is going to be with us for a good while yet. It is going to be some time before we worry about losing the stability of inertia.

     



     

    Not hypothetical at all.  South Australia already has a huge battery bank, and it appears to be doing a good job. https://reneweconomy.com.au/how-the-tesla-big-battery-kept-the-lights-on-in-south-australia-20393/ 


    It isn't intended to run the whole grid for hours on end.  It is there to store enough power to handle any short-term peak load, or sudden losses of supply.
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    Surely this article is joking. a 44 MW help when GW are connected is not going to do much at all. I don't know what the total consumption in SA was, but probably not all that much. This is only about 1000 cars worth of battery, and it saved the day? I suggest it was the industrial load shedding of aluminium heating which really did the trick.


    I would be very surprised if the solar in the UK was anything like you suggest Mike, on a nice clear sunny day in summer it could probably make the whole 40GW worth. Really? In winter the solar is a small fraction of a clear sun summer day, or perhaps they have shifted the cells to the equator somewhere. Note really bright sunlight on equator perhaps 300W output per m2, about 3000 m2 /MW, so we need about 450,000,000 sq metres or 45,000 hectares. In the UK now you would be lucky to get 50W, so 250,000 Hectares. Where are they, all 45,000 hectares of active surface for 40 GW! I rather doubt there are more than 50 Ha total.
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    Well round here there are fields of the damn things springing up on every 1000 sq meter scrap of  land that would be too rough to plough and cannot get planning permission for a housing estate . The sort of land that  would previously have been supporting sheep or pigs.  In some cases the sheep and the panels seem to co-exist, though I do not know how well the cable protection will last. Not seen pigs & panels yet - I guess they dig too much.
    The dept of Energy statistics  do suggest that as of dec 2019 the UK has solar panels installed of total name plate capacity a touch over 13GW nominal (and GB without NI a touch under, more like 12& 3/4 ) . In principle then if the whole UK were ever all sunny at once, we might muster a quarter of our daytime supply I suppose.

    Now given the actual metered generation history suggests about 10% of that on average over all days of the year (more on sunny ones ?) I am inclined to agree the gridwatch figures that imply 1.5GW today are probably an over estimate - sky is clear here with odd clouds, but I do not know how sunny it is in other parts of the country. That was not really my main point- the main point was a large fraction, maybe half, of the generation with inertia on the grid has gone since it was first designed.
  • Former Community Member
    0 Former Community Member

    mapj1:

    That was not really my main point- the main point was a large fraction, maybe half, of the generation with inertia on the grid has gone since it was first designed.




     

    And perhaps, more importantly - should we be concerned ?


    Regards


    OMS
  • 0
    Big batteries are over here too, doing the same thing. For example
    https://stateraenergy.co.uk/Energy%20Storage%20Facility/pelham-storage/


    ...And in the August 2019 grid wobble, National Grid credited EFR/FFR providers which included batteries, with sustaining the frequency enough to avoid further outages.
    https://www.nationalgrideso.com/information-about-great-britains-energy-system-and-electricity-system-operator-eso

    To save you reading (final report, p4)

    All the “backup” power and tools the ESO normally uses and had available to manage the frequency were used (this included 472MW of battery storage) to stop the frequency fall (at 49.1Hz) and being recovering it towards 50Hz.



    As Simon Barker says, these plant are designed around a very short duty cycle, but also very fast response times, primarily to provide this function (normally less dramatically than the above event mind you). National Grid procures this service directly, just as it does other reserve services. It is not the same as long term storage, which would most likely be better suited to other technologies (flow batteries anyone?) that may struggle to react quickly enough to frequency events.


    Lastly, worth looking at the requirements for G99... All mid-size generators (>1MW), including inverters, now have to incorporate a frequency response mode featuring a droop curve (albeit asymmetric, depending on size, but the point is it responds to network loading), plus feed in to / ride through close in faults, limited network voltage control and provide a DNO control interface.
    https://www.energynetworks.org/assets/files/electricity/engineering/engineering%20documents/ENA_EREC_G99_Issue%201_Amendment_5_(2019).pdf
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    What really comes out of that article about Australia, is not the battery at all, but rather just how dependent they are on coal - 5 out of 6 GW in New South Wales and Queensland, and 3.7 out of 3,8 in Queensland ! 

    (NEM is not a state, it is a National Electricity Market, i.e the totals..  and 19GW total - is that really all  ?)

    And given the space and climate how little they make use of either wind or solar.
  • Former Community Member
    0 Former Community Member
    Coal is however cheap to mine, and they make a big profit exporting huge quantities of it - burning a bit along the way makes good economic if not environmental sense


    However, the hard of thinking believe the recent fires are a warning from the sainted Greta to mend their ways  - who was it said, they have sown the wind and now shall reap the whirlwind - ahh yes, I remember now.


    Regards


    OMS
  • 0
    Where are you Mike, there is little point in solar past Birmingham? Although it is often sold, the sun angle and latitude is the controlling factor and even southern England is not very good.
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    mapj1:

    Well round here there are fields of the damn things springing up on every 1000 sq meter scrap of  land that would be too rough to plough and cannot get planning permission for a housing estate.




    Well, that may be the best use of the land. Around here, a parcel of land has been isolated by the creation of a new road, but on the other side of the road there is already a solar farm. More panels may be somewhat unsightly, but they certainly beat the prospect of extra traffic which would negate the benefits of the new road.

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