MWh vs Instantaneous MW vs MW Demand

© Copyright 2012 Rod Hughes Consulting Pty Ltd

Note - if the navigation pane on the left of this window is not visible, click the 2-pane icon on the top bar


 

Most power engineers would agree that the concepts of MW vs MWh is quite straight forward.

However when it comes to metering, there is  avast difference between Instantaneous MW and MW Demand!

Also depending on your Demand Interval, the same loading can produce two very different bills!

Suppose your billing period is once a month.

Also suppose your entire energy usage occurred in a 50 minute period on one day as follows:

1.4 MW for 20 minutes (0.33 hrs), switched that off then
0.8 MW for 15 minutes (0.25 hrs) then switched that off then
1.65 MW for 10 minutes (0.165 hrs) and the switched that off and then
8.6 MW for 5 minutes (0.125 hrs)

So just looking at the instantaneous MW and total MWh the chart is as follows (click image to enlarge):

Clearly the peak load connected was 8.6 MW and overall you consumed 1.65 MWh

 

Now depending on what type of metering arrangement you have with the utility, or if you have three different meters configured differently, you would get these different results on your bill at the end of the month.

a)    30 minute fixed Demand Interval:  1.65 MWh and 2.38 MW Maximum Demand

b)    15 minute fixed Demand Interval:  1.65 MWh and 3.98 MW Maximum Demand

c)    15 minute sliding window Demand Interval: 1.65 MWh and 3.98 MW Maximum Demand

Note the sliding window doesn't have the same saw-tooth restart at the end of each Demand Interval (because it does not end, just is recalculated) but obviously has the same average demand calculation every 15 minutes when the period coincides with the fixed window and so has the same Maximum Demand on the bill.

 

 

Contact Me

Skype: (ping even if showing offline)
My status

Email Me

A phone call is nearly always welcome depending on the time of night wherever I am in the world.
Based in Adelaide UTC +9:30 hours e.g.

April-SeptemberNoon UK = 2030 Adelaide
October-March:Noon UK = 2230 Adelaide

  Office + 61 8 7127 6357
  Mobile + 61 419 845 253



Extra Notes:

Disclaimer
No Liability:
Rod Hughes Consulting Pty Ltd accepts no direct nor consequential liability in any manner whatsoever to any party whosoever who may rely on or reference the information contained in these pages.  Information contained in these pages is provided as general reference only without any specific relevance to any particular intended or actual reference to or use of this information. Any person or organisation making reference to or use of this information is at their sole responsibility under their own skill and judgement.

No Waiver, No Licence:
Whilst the information herein is accessible in the public domain, Rod Hughes Consulting Pty Ltd grants no waiver of Copyright nor grant any licence to any party in relation to this information.