Solar production when its dark? - Page 1
Forum section: electronics / general

author: SpookyGhost
author_rank: Contributor
timestamp: February 06, 2022, 02:04:46 am
content: I have an IoTaWatt power measuring device, and it seems to be accurate during the day, but at night I'm seeing around 15w of productionIs this possible production from moonlight, street lights etc, or is this probably something else?Since I'm measuring after the Envoy I thought it would be current powering the Envoy, but I have the box checked to allow negative usage, and its still showing positive.Another thing I noticed is that the power factor was 1 which is what I'd expect, but then dropped when usage dropped off. Is this expected?

author: trobbins
author_rank: Frequent Contributor
timestamp: February 06, 2022, 10:35:37 am
content: sure is light at night.

author: f4eru
author_rank: Super Contributor
timestamp: February 06, 2022, 11:02:08 am
content: It could be imprecision of the measurement device.It could be a power consumption of the inverter at night that the measurement device strips the sign away, for convenience reason.It could be productionIt could be a combination of those.Try disconnecting the DC path in the night, then disconnect the AC of the inverter, to see if it changes anything...

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 06, 2022, 01:38:14 pm
content: It's the offset or noise floor of the meter. Easy workaround is to round production below 20W to zero.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 06, 2022, 02:45:59 pm
content: Why don't you cover the sensor with a SOLID cover and find out if the source is solar of just an error in the sensor?You also said that it appears to be generating 15W of power in the dark. Have you measured the output voltage and current directly to see if it really is producing power?

author: SpookyGhost
author_rank: Contributor
timestamp: February 06, 2022, 02:52:04 pm
content: Quote from: trobbins on February 06, 2022, 10:35:37 amI know this was meant to be snark, but yeah, there is... There is a lot of light pollution here in the city, there is the moon, and there is a lot of outdoor floodlights in my yardI didn't think it was unreasonable to think that it could be producing a measly 15w of power on a setup that uses does 13kwQuote from: f4eru on February 06, 2022, 11:02:08 amI did check the option to allow negative current, so I'd hope it would switch to -15w, but never did. But I think you might be right that its just the imprecisionSadly I can't disconnect the DC, as its Enphase Micro Inverters, I can disconnect the AC and try thoughQuote from: NiHaoMike on February 06, 2022, 01:38:14 pmThanks, I'm trying to figure how I can do that. Seems like it would be the easiest optionQuote from: Stray Electron on February 06, 2022, 02:45:59 pmDo you mean cover the CT? Not too sure what you mean thereNo way to measure output voltage directly without getting up on the roof and pulling a panel sadly

author: ahbushnell
author_rank: Frequent Contributor
timestamp: February 06, 2022, 06:37:06 pm
content: Quote from: SpookyGhost on February 06, 2022, 02:52:04 pmI think he means to cover the solar panels.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2022, 07:02:59 pm
content: It's almost certainly a small error in your measuring system.The Enphase inverters will go to sleep once their input power is low enough, and then they will draw a small recirculating current due to capacitance--the phase angle will be +90 and the PF will be zero. Perhaps your measuring system reads that incorrectly. If your inverters are awake and producing power, they will be reporting as well--so if you have per-panel reporting the Envoy should tell you that and if not, it should still give you the aggregate production amount.Remember how your eyes work with varying brightness. Full moonlight and street lamps may be enough to see by, but the actual light intensity is hundreds of thousands of times smaller.

author: SpookyGhost
author_rank: Contributor
timestamp: February 06, 2022, 07:20:02 pm
content: Thanks, that makes sense. Need to figure out how to get this to read correctly then in that case. Can't cover the panels, I have 45I have one CT on the wires in the lever disconnect after the Combiner which is then doubled. I'd love to move the CT into the combiner and do what the Enphase CT is doing and just get all of one leg from the solar circuits into one clamp, but there is not enough slack to get them into one CT. The other thing I could do is throw a CT on the other leg and see if that then makes it more accurate vs the doubling

author: tszaboo
author_rank: Super Contributor
timestamp: February 06, 2022, 07:39:31 pm
content: No, it is not night light, unless you are from Alaska.My system can switch on with as low as 5W output, and it is off during the night. Human eye perception is logarithmic, you get a million times more light power during daylight, than the brigthest nights.Its a magnetization issue with your hall sensor or smt like that.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 06, 2022, 09:43:47 pm
content: I almost wonder if it's reporting |P| and that's actually theconsumptionof the aux power, controls, standby, whatever sort of stuff.Could also be quantization noise, offsets, phase shifts, etc., all those tricky things that need to be balanced just-so for an accurate measurement. Hey, it's not revenue-grade, right?...Tim

author: TimFox
author_rank: Super Contributor
timestamp: February 06, 2022, 10:17:30 pm
content: Your reported value is just over 1/1000 times the daylight power. From the table above, that's brighter than twilight. However, is there a strong streetlight nearby?

author: trobbins
author_rank: Frequent Contributor
timestamp: February 06, 2022, 10:48:10 pm
content: Quote from: SpookyGhost on February 06, 2022, 02:52:04 pmNo snark intended - but exactly as you point out. I have seen PV data showing response from a full moon. How your PV modules convert that radiation profile, and how your PV inverters generate power from any non-zero V-I is another aspect entirely which weren't part of your first post.Whether your PV inverters could be responding in a way that is interpreted by your monitor as a power flow may be assessable if you have a way to isolate part of the inverter AC distribution (given a 13kW total). You also have moon phases and your own control of yard floodlights to sign off on that aspect. You may also be able to do a calibration test if you are competent to clip in something like a 20W resistive load to the PV generator side of the power monitor at night.

author: SpookyGhost
author_rank: Contributor
timestamp: February 07, 2022, 12:06:12 am
content: Alright, well there is for sure something messed up with the monitoringHere is switching to generatorIts a line side tap for the solar, so it should have zero impact

author: bdunham7
author_rank: Super Contributor
timestamp: February 07, 2022, 01:45:35 am
content: Quote from: trobbins on February 06, 2022, 10:48:10 pmI think the power from a full moon is something like 2.5mW/m2.But according to this article, moonlight won't work anyway because it is reflected rather than direct.https://energis.com.au/2015/11/can-solar-panels-produce-electricity-by-moonlight/"The moon does not generate its own light like the sun does and the reason why the moon lights up is because the sun’s light energy reflects off the moon’s surface area, thus creating the moon to shine. The moon produces no photons and none of its own light so unfortunately, it is not able to charge solar panels."

author: Cerebus
author_rank: Super Contributor
timestamp: February 07, 2022, 02:14:01 am
content: Quote from: bdunham7 on February 07, 2022, 01:45:35 amThat's all very well, but I don't see them making allowance for constructive interference between solar photons and lunar darkons.

author: SpookyGhost
author_rank: Contributor
timestamp: February 09, 2022, 12:41:29 am
content: Alright I got more info here, this is really bizarre. I think I got the 14w of production figured. I swapped around some CT's, flipped it around and got it to report correctly. Now it reports -12kw in the day, and +10w at night, which is probably the envoyThe picture above with the whacky lines on generator are because the VT's were now completely not on the same power source. I need to add a third VT to reference the grid power and tie the solar to itBut here is the odd thing, the VA still shows 1000 ALL NIGHT, and it shows 4a ALL NIGHT. I thought the monitoring was weird, but I got my clamp meter, and sure enough it reads 4aIf I put it in Min/Max, It reads 0a min and 4a max. Whats going on here?

author: bdunham7
author_rank: Super Contributor
timestamp: February 09, 2022, 12:49:00 am
content: Quote from: SpookyGhost on February 09, 2022, 12:41:29 amThat is the reactive current due to the capacitance of the microinverters that I mentioned before. If you were to analyze it more closely you'd see that even though the apparent power (VA) and current seem pretty high, the PF is near zero, the phase angle of the current is almost +90 degrees and the real power is miniscule.

author: SpookyGhost
author_rank: Contributor
timestamp: February 09, 2022, 12:51:05 am
content: Very interesting. ThanksI never really put it all together when you said it beforeYes, you are right. The PF drops off the chart once it gets past 0.1pf

author: SpookyGhost
author_rank: Contributor
timestamp: February 09, 2022, 12:53:47 am
content: Is there anything I could do to improve the reading? Ideally I'd like it to read 0a at night

author: uer166
author_rank: Super Contributor
timestamp: February 09, 2022, 01:26:06 am
content: Quote from: SpookyGhost on February 09, 2022, 12:53:47 amWhy would you want it to read 0A, when in reality it's actually 4A? Sounds like you want a power meter functionality instead of an RMS current meter.

author: bdunham7
author_rank: Super Contributor
timestamp: February 09, 2022, 01:36:24 am
content: Quote from: SpookyGhost on February 09, 2022, 12:53:47 amIf you want it to read 0 amps, you'll need to put in a disconnect contactor of some sort. If you want a zero power reading, I'm not sure that's any better because there actually is some power being dissipated, just not the 1000+ VA apparent power.

author: EEVblog
author_rank: Unknown
timestamp: February 09, 2022, 02:02:19 am
content: No way this is moonlightI ran the numbers once on that and it's practially nothing.It's almost certainly something in the setup.

author: SpookyGhost
author_rank: Contributor
timestamp: February 09, 2022, 02:03:12 am
content: Quote from: EEVblog on February 09, 2022, 02:02:19 amJust thing about all the production on the solar roadways at night!

author: f4eru
author_rank: Super Contributor
timestamp: February 09, 2022, 08:09:38 am
content: those 4A is the result of many capas in the EMC filters of the microinverters.It's not a problem. It's a solution.