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ESB usage data

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    #32
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    https://www.boards.ie/discussion/comment/122326970#Comment_122326970

    Sum two consecutive half hour kW values and divide by 2, not a straight divide by 2.

    Each half hour kW value sustained for half an hour would have an effective unit of kWh/2, sum the two half hour period to get a full hour then divide by 2 to change the unit to kWh.



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    #33
    coylemj
    Registered Users Posts: 25,437 ✭✭✭✭coylemj


    Each half hour is not kW, it's kWh. A kilowatt is a rate of consumption at a point in time and does not get reported by the meter. Your kW number will go up and down during each half hour, depending on what appliances are in use. The kWh number is the cumulative energy consumed.

    The 30 minute number in the downloaded file is the number of kWh you consumed in that half hour.

    Using the car analogy, kW is your speed as indicated by the needle on your speedometer, kWh is the number on the odometer.

    What the meter measures is total energy consumption in your house, it reports this every 30 minutes, in kWh.



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    #34
    prosaic
    Registered Users Posts: 182 ✭✭prosaic


    I understand what kW and kWh are. kW: thousands of joules per second. kWh: Energy used in 1 hour where the power is 1 kW (or by formula for different power levels (P in kW) and lengths of time (t in hours): E=P*t. 1 watt = 1 joule/s etc etc.

    If you want more pedantic, 1 Joule = 1 Newton * 1 meter There are various other derived measures of energy, such as 1 coulomb * 1 volt. The definitions of SI units get a bit confusing here and it has changed a bit over the years since I were a lad. Energy is more fundamental than voltage so the volt is defined in terms of energy/power. Funny that, since we usually think of a volt as more basic than energy. End of pedantry.

    The Chizler, you're summing two half hours and dividing by 2 which is the average of the power for the two half hours (assuming the quantity involved is power). To convert from power to energy, E=P*t: E=P*0.5. So it would be divide by 2 to turn it in to energy. If I run 1 kW for an hour, that's 1 kWh. If I run 1 kW for 0.5 hours, that's 0.5 kWh, etc.

    The HDF file (that I have downloaded from ESBN), what it has is power, not energy. The top of the column says kW, not kWh. The numbers correspond, approximately, to what I have on my Electric Ireland bill, so I'm happy that the calculations are correct. Coylemj, I think you may be getting a different version of HDF where the column has kWh, where mine has kW.

    My question currently is really: why is there a discrepancy between the totals given in the HDF and the units used as given in the electricity bills over a period of nearly 1 year.

    In my earlier post I wasn't fully sure I had the HDF figured out, but I think I have it clear now.



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    #35
    coylemj
    Registered Users Posts: 25,437 ✭✭✭✭coylemj


    I discovered the reason for the confusion. While BGE only gives me the kWh number, ESB Networks will allow you to select kW or (Calculated) kWh when you register your MPRN and ask to download your usage data.

    So I agree that to convert the 30 minute kW number to kWh, you would need to divide by two. Because if you ran a 1 kW appliance for all of the 30 minutes, the kW number would be 1 but you'd have only consumed 0.5 of a kWh in that 30 minutes.



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    #36
    MickH503
    Registered Users Posts: 493 ✭✭MickH503


    https://www.boards.ie/discussion/comment/122327173#Comment_122327173

    Out of curiosity I checked the same thing with my data. I have a smart meter on a standard 24 hour plan. My meter reading gets "taken" in middle of every second month, but my billing period is a calendar month, so all my bills are estimated.

    Comparing the ESB Networks HDF file data to the usage in my bills, it is sometimes higher, sometimes lower. The worst it was off by in past 9 months was 43kWh, the closest was 2kWh.



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    #37
    prosaic
    Registered Users Posts: 182 ✭✭prosaic


    Since getting the smart meter set to be used for power export (I think that was the time), it has been recording the meter remotely so we don't seem to get the absolute units reading on the bill any more. We get a number of units used for each of day/night/boost.

    The usage period is given on the 1st page of bill. I make comparison in the HDF file for the exact same date range and day/night/boost periods.

    I would expect there to be an exact match except for rounding errors. I would expect rounding errors to be fairly small and that these would cancel out over a few months.

    Post edited by prosaic on


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    #38
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    https://www.boards.ie/discussion/comment/122329595#Comment_122329595

    The meter reports energy consumption in units to the ESB over GSM but not at half hourly periods. Realistically there are going to be gaps in the data when reception is an issue, and they probably stagger transmit time so they don't get 1 million texts all at once whenever they report.

    This data wouldn't look very nice presented in its raw form (though it would be nice to have the option) so the ESB average out usage across the day so you have a data point for estimated power for every 30 minutes of the day. The HDF presents this as a time series of power estimates every 30 minutes.



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    #39
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    https://www.boards.ie/discussion/comment/122329785#Comment_122329785

    The average of the power for two half hour periods is the same as the average power for an hour, which is the definition of a kWh. I think the confusion is some people are thinking in half hour energy blocks and some are thinking in hours. If you want to break your energy usage into half hour chunks then of course divide by 2 works.



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    #40
    prosaic
    Registered Users Posts: 182 ✭✭prosaic


    I use half hour energy block since that's the interval in the HDF file. Glad we're all square .(⌐⊙_⊙).



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    #41
    coylemj
    Registered Users Posts: 25,437 ✭✭✭✭coylemj


    I don't understand why ESB Networks say the kWh number (if that's what you ask for) in the HDF file is 'calculated' - surely the meter principally measures your consumption in kWh? Where does the kW number comes from?



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    #42
    prosaic
    Registered Users Posts: 182 ✭✭prosaic


    I didn't ask for kW. Someone mentioned, maybe up thread(?), that it might depend on which provider you're with.

    I don't mind kW or kWh but I don't want to chop and change.

    One reason to quote average kW would be where the time interval varies, e.g. an hour or two of missed data. It could make for easier scanning for electricity consumption spikes. If the interval sizes vary the energy varies but the power might tend to be more constant.



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