Revisiting accuracy

It’s been a long time since I posted an update on the accuracy of my home IoTaWatt. I’ve had continuous monitoring with an IoTaWatt since Jan 17, 2017. The hardware unit has been upgraded several times as new versions were developed, but each time I just moved the SDcard to the new unit and picked up where the old one left off.

So I dug out my log and noticed that’s been a year since I last checked the IoTaWatt against the utility meter and the two revenue grade EKM meters that I have on my heat-pump and hot-water heater.

Here it is for almost two years:

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Impressive. Does this setup use its own calibration values?

I just had a look at the last 6 months of my data and my mains kWh differs by less than 1% from my utility bills. I’m using an Ideal 77DB-06-09 VT and SCT013-000 CT on the mains with stock standard calibration tables. I’m happy. :slight_smile:

The CTs use the standard table calibrations. I did calibrate the VT as described in the docs using a voltmeter.

I love this thing, it has helped me show Diakin that their heat pump uses heat strips when they said it shouldn’t (15KW!), as well as learned some behavioral things ourselves. The odd thing for me is I’m about 1 day behind it appears with IOTAWATT and Utility Billing, so I have to adjust back a day for my reporting to match. The odd thing (and maybe this is just due to my local Seattle City Light Co) is that IOTAWATT will show much less usage for a few days, and then SCL will catch up and it all evens out. I’m not sure how ‘normal’ this is, but it’s frustrating when trying to validate data.
Once I move my outdoor power to my garage subpanel, I’m buying a second IOTAWATT to monitor those better. I seriously feel all home owners should have an IOTAWATT. I recommend them to everyone.

Do you get daily or “real-time” data from the utility?

I would expect that to be the other way around. The IoTaWatt always has up to the second totals, but if there is a lag or lapse in the meter reporting to the utility (assuming the utility is doing daily reporting) then the IoTaWatt would report more. The other possibility is that if the utility estimates and then corrects when the data comes in.

I think all revenue meters are required to have a visible display that consumers can read, so your meter should have one. It would be a worthwhile exercise to record the meter reading daily and reconcile with both the IoTaWatt and the Utility report. When I’m doing this, I usually snap a picture of the meter for the reading. Most phones will data/time-stamp the photo.