One problem with the way TLC's demand charging has been implemented to date is that load control for different customers is applied via different channels and those channels are typically controlled at somewhat different times. This is true even within a single GXP related area - "Taumarunui" for example, or more precisely, all those customers whose supply comes through the Ongarue sub station. The end result is that some of the measurements to find "peak demand" have occurred across different periods for different customers, even though they could well be neighbours.
While there is typically a fairly high degree of agreement between different channels, the small differences can still easily lead to situations where customers are not treated equitably, accentuated by the fact that the underlying TOU meter readings are only at a half hour resolution. Therefore in my own recent submission to TLC (following publication of the Sapere and NZIER reports) I have recommended that only qualifying periods of control common to all relevant channels in a single GXP area be used in any future system based on measuring demand during load controlling.
The reason is that for a customer with a demand (TOU) meter, their final demand value is determined from the periods that were fully controlled and also only those periods that were long enough. For the 2009 and 2010 winters this meant they had to be at least three hours long. The TOU meters record consumption data every half hour, aligned with clock half hours (unless the meter clock is inaccurate for some reason). It also wouldn't be fair or correct to include half hours that were only partially controlled as this would mean some controllable load (e.g. water heating for many customers) could be included which is contrary to the underlying philosophy of TLC's approach - controllable load is not meant to contribute to your demand. So this means that at least six consecutive fully controlled half hours were needed before a potential "peak demand" could be calculated by calculating the average load over each such three hour block. Only periods passing that test (and also falling in the 1 June through 30 September period) are looked at when determining a customer's single highest average demand over a three hour period.
One example is shown below, comparing two channels from the same area. What is displayed are only the qualifying load control periods for the two channels, aligned side by side by date and time so you can see at a glance where the main differences are. In other words, the blocks of time shown are only those remaining after discarding all periods of full control less than three hours long. So while there was actually a lot of other load controlling on these two channels, (including across September) none of that appears here because it didn't qualify.
The dates and times of qualifying periods for the first channel are on the left, aligned where possible with the corresponding period on the second channel on the right (with "<>" separately them). When one or the other side is blank then we know that there was either no controlling at all (probably not likely), or whatever controlling did that occur wasn't both long enough and continuous. These cases are, in my opinion, the largest problem as customers on one channel are being "measured" for that "network peak" but those on the other aren't.
Of course, even when there are corresponding qualifying periods on both channels, there are still often small differences in the start and end times. For example, on June 02, the qualifying period on the first channel shown ended at 21:00 (9 pm) but for the channel shown on the right the latest time measured was 20:30 (8:30 pm). Probably less than half match "exactly" - those are highlighted in green to make it easier for you to look at those that differ. The largest difference appears to be on July 11 where the first channel has an extra 1.5 hours for some reason, all the way through to 22:30 (10:30 pm).
When processing load control periods that have different start or end times (as per the June 02 example) the extraneous half hours would be ignored for purpose of calculating demand values (kW Load) under the modification to the rules I have proposed. That is to say, only the fully controlled half hours common to all relevant channels would be considered and that would mean all demand meter customers in a given GXP area would be measured against exactly the same set of half hours.
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