Solar production numbers low

#1

I just installed sense solar into my sense which has been running for some time now as I got a new solar system. My solar production numbers reported by sense tend to be anywhere from 9% to 18% low depending on the day. It is also curious that in the non solar hours I show apx 9-10 watts of negative solar.

Should I recalibrate?

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#2

9% to 18% low compared to what ? If you are comparing against power data coming out of your inverter, realize that inverters, unless they are specifically rated as “revenue-grade”, tend to run high compared to what they actually deliver to the house for a variety of reasons. But if you have a revenue grade inverter or a separate revenue grade meter on the house feed-in, then I would question the Sense. My solar inverter runs 4% higher than Sense, but Sense data squares with my electric company meter almost exactly.

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#3

Hey @gary2. Go ahead and submit a support ticket via https://help.sense.com/hc/en-us/requests/new. The negative at night could be your inverter’s power draw, but it’s hard to tell without data in front of me. But the discrepancy is odd, so we should definitely take a look!

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#4

That is compared to my solaredge inverter numbers. I also have a revenue grade meter which when I checked the other day was pretty close to my inverter numbers.
If it was a few % I’d be OK as I don’t expect it to be perfect, but the wide variation is puzzling.

For the last few days it was 9% , 18 % and 11 % lower than my inverter. This seems to be way more than I would expect. Even if the negative number at night is the inverters power draw that would on my worst day account for less than 0.5 %. of the discrepancy.

I’d like to figure out if the 18% is due to sense or my inverter, and if I need to recalibrate or something.

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#5

I just checked my inverter and my SREC meter. They match perfectly. On average sense seems to be reporting about 10% low on generation, but it does seem to vary on a day to day basis.

I opened up a ticket.

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#6

My sense cuts out for periods of time, then cuts back in without intervention. I have notified the Sense people of this, nevertheless, when it does this during the day, my solar numbers are low too by a few KWh at a time. Sense is not good enough yet to keep accurate track of solar or usage, just because of these cutouts.

#7

I’m not seeing drop outs on my account it just seems that sense reads a little low on the production. I calibrated a couple of times on Saturday with good solar generation. Sense instantaneous numbers seemed to be about 8-10% lower than the numbers on my inverter (Sense does move around a lot more).

My inverter production numbers match my SREC meter numbers almost perfectly (<1%) Sense seems to be much lower. On higher production days it is running about 8% low. On some other days it has been as much as 18% low.

Over the month it has been about 7% lower than my Inverter/SREC meter. There is likely a small offset in sense due to it recording the inverter power during the night time, but this is a small error (2% on a rainy day, 0.3% on a sunny day)

I certainly can live with it, but the error was higher than I expected.

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#8

Right, sense is not accurate. There are only two reasons I can think of that would result in such a problem. The first is calibration of the voltage and current measurements. I have no idea how the calibration is done, so I can’t comment. The only other reason is if it stops measuring the voltage and current for periods of time, so the total is recorded low and incorrectly. Certainly, I also see negative 8-10% errors, which are very high, so I doubt it is a calibration issue. On my system, I have three measurements being made of my solar production. The first is the electricity company’s meter, the second is the meter on my inverters. These two agree exactly within the precision of the numbers on my electricity bill. The third measurement is the Sense numbers, which are not reliable, with most days being different from the report from my inverters. I have 40 micro-inverters, which report to their own base station to produce the total solar production.

I agree that my Sense reports numbers that are always lower than the actual production, so it is a one way error that can be explained by dropouts, and I have not been able to come up with another explanation. Clearly, this is an accuracy problem, not a precision problem.

Also, I agree that there is a small offset at night. I think “recording the inverter power” means that Sense is likely recording the quiescent power used by the inverter(s). I do not know whether or not the number is being subtracted from the total production numbers provided by Sense’s reports, but it is not being baseline subtracted from Sense’s meter.

As for living with it; its wrong, plain and simple. It means that all the Sense numbers may well be out one way or another, so how can you rely on reported appliance power and energy usage to make decisions? While sense is a great device, and addictive, it has flaws too, including misidentification of appliances when they turn on and off. Again, this is a “10%” problem, but it is there nevertheless.

I decided to keep my Sense - Why does it go offline at 5 and 8pm often?
#9

I’m interested in both of your setups, since I see just the opposite. My Sense agrees very closely with my PG&E net meter, and my inverter data is about 4% high. For me, the single inverter and feed-in to the main panel (and Sense) are about 8 feet apart. Wondering a few things:

  • Do you have net meter or a dedicated power company meter on your solar feed-in, plus a net meter for the whole house ?
  • How far apart is the inverter (or micro inverters) from the feed-in/Sense ?
  • Where is the “power company” meter monitoring the solar in relation to the inverter and feed-in ? Close to the output of the inverter or close to feed-in / Sense ?
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#10

I have a power company “net” meter, which is within a very few feet, say 3-4 feet, from my electrical panel, where the sense probe is located to probe solar production and electrical usage. The distance of the micro-inverters is not relevant, as they all report to their base station which is within a couple of feet of the Sense probe. Of course, the micro-inverters themselves are all mounted on their own solar panel spread out over the roof.
With regard to your inverter data being high. I am talking about the total power kWh generated per month as reported by the three sources. Instantaneous energy data are another matter. I have not monitored instantaneous energy data that closely because, my microinverter data are only updated every 15 minutes, which makes instantaneous data impossible to obtain from the microinverters. However, the peak energy data reported by my microinverter setup seems to be a little lower than the peak energy data reported by Sense, so if you are talking about peak energy data, rather than power, then I think I agree with your 4% number.

#11

I have 2 meters. These are both revenue grade meters (+/-2% accuracy):

A net meter to the power company. This records Power in (from Utility) and Power out (to Utility) It does not record total solar power generation
An SREC meter This records the total power produce by my solar array. This is total solar production and matches very closely (<1%) to the power generation reported from my inverter.

Set up is as follows:

Solar panels with Solar edge optimizers connected to solar Edge inverter
Solar Edge inverter connected to SREC meter
SREC meter connected outside shutoff (40 amp breaker) then to tap connector on the power lnput to the Panel
Sense solar sensors on the tap connection
Sense power sensors after the tap connection on the main power input to the Panel

Main Net meter connected on the Line side of the main power input.

Distances are very short.
Maybe 1-2 Feet between the Inverter and the SREC meter
Maybe 3-4 Feet between the SREC meter and the Panel
Maybe 3-4 Feet between the main meter and the Panel

If I compare the SREC meter (this is the “golden meter” that measures power generation) to the Inverter production numbers these match within 1%
If I compare the SREC meter to the sense production numbers the SREC meter production over a day is always higher than Sense by 7-18% typically about 8%

After I ran a sense recalibration on Saturday I compared the current power numbers (W not Wh) (instantaneous) between Sense and My Solar Edge inverter. This is not precise as Sense changes much quicker than the solar edge, but ballpark the Sense was running about 8% low.

I have not compared the Net meter readings to the sense readings.

Gary

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#12

Your setup is very similar to mine Gary (SolarEdge optimizers connected to SolarEdge inverter, with roughly the same spacing), except I don’t have an SREC meter. When I say that my Sense matches my revenue meter, I mean that on an hourly or daily basis, the KWh used/produced read on my net meter matches the Sense usage minus Sense solar for that time period, within 1%. I’m wondering if there is some kind of constant offset from the Sense that gets eliminated by my subtraction to calculate the Sense net.

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#13

I also have a Solar Edge setup comparable with what is noted by others, i.e… net meter, optimizers, distances, etc… I have noticed Sense reported production is about 8-10% off as reported by the inverter.

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#14

Have you worked with Support on this at all? There’s a few reasons why your solar figures may be off and they can help figure out what’s going on. Other than installation errors, a possible culprit is the inverter itself drawing current in a way that is difficult for us to monitor. I highly recommend checking in with Support as they can offer additional guidance.

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