Solar Calibration ERROR !!!
So I was having some issues and tech support suggested that I re-calibrate my solar. After doing this I notice that Sense is reading my production a good bit lower than what my inverters are claiming. When Just the one large inverter was running Sense claimed production was 4,335 watts while the inverter showed 4,550 watts - Sense was only showing 95.275% of production. When I put the other two smaller inverters on line Sense showed total production of 7,282 while the inverters show 7,774 which is only 93.67% of production. Not Good 
Pretty certain this is what I’ve been hot on since the very start.
Well you have been correct! This is the first time I actually took realtime measurements when things were stable enough to see what was going on.
1 Like
Don’t bother trying new cts, I’ve already ruled that out 
1 Like
I’ve seen what appears to be about a 5% less on my Sense solar CT’s vs the reported value of my solar production meter (which even if not correct, is what is used for my SREC calculations).
My solar panel monitoring has issues, and are being fixed (hopefully) this Tuesday… After I get it up and running, I should be able to compare the Solar Panel production, to the Solar Production Meter, and to the Sense solar CT’s, and see how they all compare.
I’ll set up a remote webcam on my Solar Production Meter to track that all day (Total power and instantaneous power and voltage) and compare to my Solar Panel info (reported every 5 minutes) and Sense CTs (reported continuously).
The error differences might be linear, or may follow some other curve based upon power (actually amps). Obviously, it will be easier if linear and thus a simple percentage. However, as you reach some value (80+ amps), I bet the curve becomes a whole lot less linear for the solar CTs.
Make sure to also have a look at the voltage reading in the sense settings.
For reference, my watt error ranges between 5-7.5% off on the real time readings (sense vs inverter), 7.5% cumulative daily total pretty consistently (sense vs inverter). When compared to the meter, it’s ranging between 3-4.5% under, so the inverter is obviously being a little generous.
Sense has reported in numerous posts they are working to fix this, and it’s important because it’s negatively affecting device discovery and recognition.
Sense is DEFINITELY under reporting solar and I proved it today. My power usage was running at only 95 watts according to Sense. I turned off my humidifier which pulls about 50 watts, both of my ceiling fans which pull about 20 watts each which represents 90 watts of usage and Sense showed me usage of only five watts. The thing is my computer system which was sleeping was showing 42 watts of usage. In addition to that I have dozens of ac adapters, several UPS systems a few electric clocks, three TVs and streaming devices on standby all the times a microwave and Fridge with digital circuits that are always on, two HVAC systems that always draw power and a bunch of other small things that draw power. My house is around 4,000 square feet - no house that size ever uses only 5 watts!
1 Like
Lol, we should have a contest. I’m at about max production, though, so this may be as good as I can do 
Think this might be affecting discovery?
Well you have me beat with both mains negative, I bet I could have gotten there if I power downed a few more things. This really sucks that now not only don’t I believe the solar numbers but I also don’t believe the consumption numbers. The numbers are now only an indication of direction. I hope they come up with a quick fix for this. Why was something like this not caught much earlier on when they tested this in the lab with standard loads???
1 Like
I have a similar under reporting issue.
Unable to see 10ths on the Sense trend side, so that accounts for some small part of the variance.
Here are my numbers for March so far:
And here is a like to my system production reports:
Just is case the Sense folks want to take a look.
1 Like
My number have been pretty close over the last week comparing my POCO meter net to Sense:
Solar production reported by my inverters is always higher, but that makes sense since there is more voltage drop between my microinveters at each panel to the ~250 ft total distance to where Sense and the POCO meter is located. Besides, I have other loads in my shop that go through the solar CTs adding to the discrepancy.
I’m starting to “win” my war with the POCO as my POCO meter NET readings are now starting to dig into the negatives and its only the 1st week of March. Can’t wait to see what the numbers are going to look like in June and July. 
No sure what voltage drop has to do with watts. As voltage goes down doesn’t amperage go up to maintain the same equivalent wattage? Isn’t that the reason when the utility has a brown out (voltage reduction) you need to be careful as the amperage your motors draw goes up and you can do damage to the windings?
Power (watts) is lost in the form of heat from the point the energy leaves the microinverter attached to each solar panel.
In my case, I have 6 strings with either 12 or 14 panels/inverters in each. They are all connected via 12 gauge wire. From the end-point of each string, I have 10 gauge wire going to 20A breakers in a sub-panel. Average distance is about 50 ft.
From the sub-panel, there is a 200 ft run to the safety disconnect where Sense is installed. This is pretty beefy 500 MCM aluminum wire, but there is still some loss.
Right now, for example, my microinverters are sitting at about 254V and Sense is showing about 248V. So that is a voltage drop (rise) of 6 V, which is a little over 2%. So that 2% is energy lost in the form of heat since due to the resistance in the wiring between the microinverters and where Sense is connected.
That seems like a very large loss for such a small distance. I don’t have micro inverters, but know there is very little drop from my big inverters to my breaker box.
Using an online voltage drop calculator, I get the following drop from one of my 14 panel strings to the sub-panel:
10 gauge Copper
50 ft
Voltage 254
Load Current 15.4 A
Voltage drop 1.54
Voltage drop percentage 0.61%
Voltage at end 252.46V
And now the 200 ft run to the main panel from all 80 panels:
505 MCM Aluminum
200 ft
Voltage 252.46
Load Current 88 A
Voltage drop 1.15
Voltage drop percentage 0.46%
Voltage at end 251.31
Those totals are:
Voltage drop 2.69
Voltage drop percentage 1.07%
There is some loss in the sub-panel, the 10 ft run of 3 gauge Cu to the 2nd meter base, and again in the fuses at the safety disconnect, which probably accounts for the other 1% of loss or so.
2% is actually considered pretty good, especially with a total distance of around 250 ft.