I have some electric power readings collected from a smart meter. With each reading there is energy consumed as shown in figure at link.

Some readings do not have energy values. So, I need to calculate these values manually in order to complete the data set. How should I calculate these missing values given the fact:

  1. The time interval between successive readings is 30 seconds

I used the formula energy(watt-hour)= power(in watts) * time(in hours), but it is not giving correct values on applying on the readings associated with energy values. How should I calculate the energy values? Is there any other approach to calculate energy values?

My calculations: Considering second reading given in figure:

Energy= power * time  //(formula)
        = 123.4582443 * 30
        = 123.4582443 * 0.00833  //(time in hours)
        = 1.028 watt- hour
    but, correct value  is 1670763.75
  • \$\begingroup\$ The math works here. What are you doing to get it wrong? \$\endgroup\$ Commented Sep 12, 2015 at 10:03
  • \$\begingroup\$ @IgnacioVazquez-Abrams, Sorry. Now, I have shown my calculations. \$\endgroup\$ Commented Sep 12, 2015 at 10:15
  • \$\begingroup\$ Have you noticed a trend in the Wh values? \$\endgroup\$ Commented Sep 12, 2015 at 10:18
  • \$\begingroup\$ Yes, there is a trend. I think this is because the time difference is too small (30 seconds) \$\endgroup\$ Commented Sep 12, 2015 at 10:25
  • \$\begingroup\$ The point that @IgnacioVazquez-Abrams is failing to make is that the "Energy" values are cumulative. The difference between the first and second readings matches the value you calculated for the second line. \$\endgroup\$
    – Dave Tweed
    Commented Sep 12, 2015 at 10:31

1 Answer 1


enter image description here

The reading of energy in the top of the final column is accumulated energy taken from power measurements that occured prior to this table. The 2nd energy reading is 1 watt hour larger than the previous reading.

From that and given that the time interval is 30 seconds, I calculate that the average power over that time period (30 seconds) is 120 watts i.e. 1 watt x 3600 / 30.

Does that help?

The fact that the power reading at 54:52 is 123.45 watts doesn't mean that it remained stable at value throughout the previous 30 seconds but it may have and the energy reading may not show enough decimal places to register this slight discrepancy.


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