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    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 5th 2013
     
    How does this work without a centralised system to take any excess?
  1.  
    Posted By: SteamyTeaHow does this work without a centralised system to take any excess?


    Brief outline on a dutch smart grid

    http://www.cospp.com/articles/print/volume-11/issue-3/features/implementing-micro-chp.html
  2.  
    Video of how the smart grid works on the dutch site

    http://www.youtube.com/watch?v=qti0BvZ_PR0
  3.  
    Steamy

    Bit more technical stuff as I know you like this sort of thing. Personally I am only interested in the fact that it works.

    http://www.federesco.org/images/PowerMatching%20City.pdf
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 5th 2013
     
    Not read the last link yet.
    But the first two are lacking in detail. And it still needs a centrally controlled grid. Also there is an assumption that more local smart grids with more distributed generation will result in more stability, dubious claim that one.

    Hopefully there will be some real efficiency data in the third link, just trying to do some work at the moment so it will have to wait. The same kind of wait that you need for clean clothes and dishes, or your car charged up to go to work :wink:
  4.  
    Posted By: SteamyTeaNot read the last link yet.
    But the first two are lacking in detail. And it still needs a centrally controlled grid. Also there is an assumption that more local smart grids with more distributed generation will result in more stability, dubious claim that one.


    Smart nodes (devices that are frequency and voltage responsive) enhance grid stability. The voltage/frequency "data" is the result of local information and available globally but requires little in the way of central control if your loads are intelligent.


    Copy paste from an email of mine of an outline of what this might look like:

    Not all energy (and electricity specifically) is
    created equal. Propose categories of devices; say:

    1) Non negotiable loads. Heart and lung machines, heating and alarm
    systems, boradband, and emergency/transit lighting features.

    2) Partially negotiable loads. Stuff I don't mind turning down a
    little in an emergency. Slower kettles and washing machine heaters for
    example.

    3) More negotiable loads. Stuff that I don't mind turning off
    completely in an emergency or that waits for certain criteria to be
    met before operating. EV charging and dishwashers that wait for
    troughs in the night rate for example.

    4) Stuff I really couldn't care less about. I'll take excess Wind, PV
    or Nukes if it's there to top off the EV or preheat some thermal mass
    with a heat pump but really am not that fussed about it.


    Controls have to be piss fucking simple. I would use frequency to
    signal grid load, and half hourly data via broadband or GPRS to signal
    price and CO2 intensity (less critical if unreliable; fairly
    universal; reversion to "flat rate/peak rate" isn't catastrophic.


    Controls absolutely have to be in the hands of the consumer not the
    supplier in order to be palatable. This means intelligent nodes. From
    boggo basic 50p TRIACS dropping the odd half-cycle in devices with
    resistive heating elements to that plus a timer for "getting close
    enough to what are very predictable troughs" in white goods to perhaps
    something smarter still that I can show off down the pub/use for home
    automation via my iPhone in lighting an AV gear.


    *I* choose the CO2/kWh threshold, or the £/kWh threshold, for the
    various categories of appliances. *I* set my own demand curves. *I*
    choose what works how and when (other than emergency frequency based
    demand response). Utilities can get stuffed. Daily Mail is happy.


    Savvy smart meter operators also ought to be happy. Or broadband
    operators providing network nodes. Or cable/satellite TV operators
    providing the base for AV and home automation by extension. Or games
    console manufacturers. Or smartphone manufacturers deciding to nail
    one to the wall. (my Google Nexus 4 was £160, contract free and
    unlocked, and utterly spanks any device designed to be integrated into
    buildings in terms of connectivity and processing power per $)


    Why? Many people will be happy with the default settings out of the
    box, provided that you're reasonable about programming all new
    products with these technologies included. (any that don't have them
    don't get A ratings for energy efficiency or are otherwise taxed in
    order to raise money/punish importers of generic chinese "world" goods
    etc) The innovators/leaders/early adopters (and objectors) will want
    to set their own thresholds though, and they'll want a centralised way
    to do this. You then sell, as a service/product, ratther than imposing
    it, a way to manage your electricity demand.


    The more exposure you give the customers to true cost of generation
    the better in this respect. You must be able to play the game. (none
    of it works if all electricity is 15p/unit 24/7) Duty-free thresholds,
    or power limits below which electricity is flat rate but above which
    it is priced differently, or variable tariffs for interruptible
    suppliers, or half hourly pricing, or any of the models that already
    exist and are proven to work for larger users, would all work here.
  5.  
    Bornholm (Danish Island) is another example worth looking at.

    I don't think completely local grids are the answer myself. Balancing yes, augmented by a national grid, such that we can take advantage of offshore wind, tidal, and nukes more readily.
  6.  
    http://brightgreenisland.com/

    Here is a link to the main website for the Bornholm sustainable community project.

    Took a day trip there last August and should go back for a longer stay in the next year or two.

    Well worth a visit if you get a chance.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 5th 2013
     
    The problem with too much distributed generation is that to keep within predefined limits you have to build in system redundancy. This leads to extra losses. Would be nice to see an example of this rather than over reliance on an import/export grid or the theoretical models. Smart metering can only go so far, it can load shed quite easily, the opposite is not so easy as switch on has to be staggered. Frequency and voltage sensing are only part of the solution (works for a small AC island grid only). To do it properly load sensing is also needed. Then there is the problem with harmonics when randomly switching inductive loads on and off (your washer, heat pump and fridge). Then it has to be remembered that to load shed the load has to be on (a fridge is not often on and it is only about 100W load when running).
    Then there is the prediction side. The system engineers and statisticians that run the National Grid can predict pretty well the anticipated loads (not always but they are pretty good). So a while before a peak they have already started to run down some of the larger generators so that they do not over speed, which would increase the frequency and voltage on the NG.

    The way I see it is that if you have too much micro generation then you get instability, a case of the tail wagging the dog.
    There are ways around this, but they are inefficient and costly.
  7.  
    Steamy

    How can you say there inefficient and costly, Electric efficiency is better than coal and combined efficiency is better than coal or gas. As for costly if your already replacing an old gas boiler than the additional cost of a CHP unit is minimal. Think the UK target was 1 million old gas boilers per year which if replaced by CHP would soon have a significant effect on daily demand.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 5th 2013 edited
     
    The main reason it is costly is because coal is very cheap, gas pretty cheap and even diesel for emergency balancing is quite cheap.

    The point I am making, and have been making for a while now, is that CHP is okay for base loads or for specific tasks (like a swimming pool). Installing 1 or 2 GWe with 6 to 12 GWt of distributed generation (your million new gas boilers) is probably okay, installing 20 GWe with 60 GWt is a totally different problem. The big problem is the electrical diversity as thermal energy can be dumped easily and quickly.

    The idea of building a factory that needs low grade heat next to a power station is a bit of a non starter. How many laundries and food factories are needed to mop up the 50 GWt from just our coal power stations. Could make an awful lot of pasties, and we know where we stand on them :wink:
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 5th 2013
     
    Have read that third link you posted, more about the economic model on a very small scale. They do acknowledge that the system has technical limitations (power quality) which is pretty important when comparing to an existing system.
    They don't say what happens when the thermal stores are all full (or if they did I missed it).
    There is also a potential problem when individuals try and play the market by withholding generation.
  8.  
    You would be surprised how much energy agriculture can mop up. If "free" or "nearly free" then you can greatly extend the growing seasons for a variety of crops.

    One could also utilise the low grade waste heat for energy storage. It works rather nicely with compressed air energy storage - see here:
    http://www.lightsailenergy.com/


    RenewableJohn: "How can you say there inefficient and costly"
    -efficiency lower than that of a combined cycle gas turbine unless you have a huge heat demand
    -cost of electricity generated far higher than sum of grid electricity and a gas boiler (especially when maintenance is accounted for)

    Fuel cells as CHP at retro expo today may have a more appropriate electrical:thermal ratio than may systems:
    http://www.bluegen.info/
    But responsiveness isn't great (though 3:1 modulation isn't bad) and a £20k initial purchase price + £500/yr maintenance contract blows economy out the window.
    • CommentAuthorSeret
    • CommentTimeDec 6th 2013
     
    What sort of CHP are you asking about Steamy? There's a big difference between domestic µCHP, district heating CHP and large power plant CHP.

    Here in the UK the only µCHP systems available are heating led. They only run when there's demand for heat, any electricity they produce is a nice little bonus on top. So strictly speaking they don't need a heat store, although coupling them to one does improve efficiency somewhat.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 6th 2013 edited
     
    Seret
    Mainly uCHP, though the same problem of demand matching is probably there at the district level.
    I think they are fine for baseload, just too many technical challenges for demand matching with our current infrastructure.
    Take this morning, it is 6:20, my house is drawing about 8 kW (water, heating and washing machine), come 7:00 it will be drawing about 100 W, with the occasional spike of 3 kW (kettle) and maybe 1 kW for the cooker for half an hour at lunch time.
    So if my neighbours and I all had uCHP and we all live pretty similar (I know each side of me are up) then we would all have our uCHP running. This would be an under supply of electricity and an over supply of thermal. Where would the efficiency saving be?
    • CommentAuthorSeret
    • CommentTimeDec 6th 2013
     
    Well, given current near-zero interest in µCHP I don't think we're going to have any problems with an overabundance of it any time soon.

    Electrical output is 1kW for a unit like British Gas's Baxi µCHP, so like you say it's designed to just deal with domestic base load, with any excess only going as far as one or maybe two adjacent houses away.

    You're not ever going to have an oversupply of heat, because they're only responding to demand for heat within the home they're in anyway. It essentially works just like a gas boiler that also produces some electricity.
    • CommentAuthorEd Davies
    • CommentTimeDec 6th 2013
     
    Posted By: SteamyTea… it is 6:20, my house is drawing about 8 kWh …
    Steamy, fix that immediately!
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 6th 2013
     
    Ed, that is for my heating and DHW for the day, and the washing machine was on when I read the monitor.
    The heating and DHW come on at 4, about the lowest CO2 intensity time, day before yesterday all the hot water (200lt) was used, that is a rare day, won't know what today's usage was till midnight.

    Posted By: SeretElectrical output is 1kW for a unit like British Gas's Baxi µCHP, so like you say it's designed to just deal with domestic base load, with any excess only going as far as one or maybe two adjacent houses away.
    That is why I think they are so small, keeps the grid stable.
    The only way I could see a district system working is with quite a lot of storage and running the CHP unit at times of peak load only. May be useful for flats where gas is a danger and the space heating loads are pretty small, so mainly used for DHW and electricity.
    • CommentAuthorEd Davies
    • CommentTimeDec 6th 2013
     
    Sorry, should have been more explicit: only referring to “8 kWh”.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 6th 2013 edited
     
    :shamed:
    What do you expect at 6 in the morning, shall go back and change it.

    Edit 07/12/2013
    For anyone interested, yesterdays usage was 19 kWh of which 16 kWh was between 4 AM and 7 AM. So about £1.50
    When the monitor is calibrated that will come out at about 16 kWh. Yesterday was pretty warm, about 10.2°C with a Min of 8.7°C and a Max of 12.4°C, not much wind and a bit of sun (230W.m^-2).
    Trouble is with storage heater is that I don't use any less when it is hotter than normal, just end up with a warmer house.
    • CommentAuthorSeret
    • CommentTimeDec 7th 2013 edited
     
    Posted By: SteamyTeaThat is why I think they are so small, keeps the grid stable.


    I don't think that's their main concern, I think that's just the electrical output of a Stirling engine that produces the right amount of heat. More advanced systems like fuel cells do try and up the electricity to heat ratio, as it's more valuable than heat.

    If the grid is happy with homeowners with 4kW PV systems, it could cope with 4kW µCHP too.


    The only way I could see a district system working is with quite a lot of storage and running the CHP unit at times of peak load only.


    The manufacturers do recommend coupling µCHP to a heat store if possible. The first reason is that the the Stirling engine based ones really don't like cycling, so long slow burns are much more efficient and it's easier to guarantee that if you're decoupled from demand. The second reason is so that burns can be timed for periods of peak electricity demand.

    A larger district system would need some amount of buffer in it anyway, so storage is a given.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 7th 2013
     
    There are problems when many PV systems are on the same local circuit though, the DNOs tend to put it right. I am not sure how they do it, are there automatically adjustable transformers or do they just over engineer?
  9.  
    Grumpy men manually changing transformer taps seasonally whilst muttering about flippin' PV installations IME. :shocked:

    (they're looking to automate more of the LV transformers; historically there was no need to)
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 7th 2013
     
    Power boys down here are really pleasant, though they are the ones with permanent jobs !
  10.  
    Posted By: SteamyTeaThere are problems when many PV systems are on the same local circuit though, the DNOs tend to put it right. I am not sure how they do it, are there automatically adjustable transformers or do they just over engineer?



    Should not have to rely on the local DNO. In Germany all new inverters must provide power modulation by frequency so after a predetermined cut off point the power output is gradually reduced as frequency increases. UK problems would be eliminated if they followed the tried and tested German route.
    • CommentAuthorEd Davies
    • CommentTimeDec 8th 2013
     
    I can't see how that makes any sense at all; the frequency of the national grid has practically nothing to do with with loading conditions on the local network.
  11.  
    Posted By: Ed DaviesI can't see how that makes any sense at all; the frequency of the national grid has practically nothing to do with with loading conditions on the local network.


    Simple explanation here

    http://www.dynamicdemand.co.uk/grid.htm#

    In Germany I believe the inverters start load shedding at 50.2 Hz but then they do have far more solar and wind to contend with.
    • CommentAuthorEd Davies
    • CommentTimeDec 8th 2013
     
    The national grid won't go over-frequency just because the tappings on one particular local transformer (which have been set to prevent an undervoltage when everybody's heat-pumps are running in the winter) are too high to prevent an overvoltage when the heat pumps aren't running in the summer but the PV is producing at maximum.
    •  
      CommentAuthorSteamyTea
    • CommentTimeDec 8th 2013
     
    I think that undervoltage is the bigger problem because that increases the current flow, G83 sorts it all out anyway, keeps it very tight.
    I also do not have any way of working out how much frequency will change for any given change in demand. Probably quite slow.
    The way I understand it at the moment (from lots of reading of the problem) is that they use a number of interacting models. The main one is a time series statistical one i.e. they know roughly how much is needed and when, then a frequency/voltage one as that keeps everything within parameters and finally a load sensing one as that can connect and disconnect generation or loads.

    The way I see large scale micro generation is similar to a college class of school failures, they all think they know what is best for them so act independently (and noisily), but can be trained to work together some of the time. After a while they are fit enough to go out but are of lower quality and will still cause problems every now and again.
    I would think that a local grid will lots of micro generation on it is a pretty low quality noisy place (electrically).

    Anyone know how well an inverter tracks grid frequency?
    • CommentAuthorEd Davies
    • CommentTimeDec 8th 2013
     
    Posted By: SteamyTeaI also do not have any way of working out how much frequency will change for any given change in demand.
    Frequency doesn't depend on demand. It depends on the imbalance between generation and demand.
   
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