Do I have 'perfect' solar panels, or is my Goodwe XS wacko (most likely)

[prutser]

I just installed 2 PV panels and a Goodwe GW-700-XS-11 inverter.
Yesterday at the end of the day, switched it on for the first time (not much sunshine anymore), the system supplied around 75W, which seemed sensible. When it became darker, the produced power dropped to approx 20W, but during the night it remained around 20W (varying slightly, so no static data).
20W in nearly  dark condition seems unlikely.  There is a street lantern at approx. 15m,  but assuming the street lantern has a 50W lamp, it will not generate 20W in 2 PV panels considering the light losses and PV efficiency 

Since this inverter is transformerless, I can imagine (due to a defect) some voltage appears at the DC terminals causing the inverter to stay 'on', however I would not expect any measured current: (current, if any) would flow in the opposite direction in such a case (this depends of course on the current sense circuit and calculations).

Tonight I will hook up some multimeters at the PV wires to see what's really happening, but I was just wondering if anyone has experienced something similar ?

[fourtytwo42]

I have two 1Kw arrays pointing in different directions in parallel.

My inverter works down to ~2W (input) before it finally gives up and it never picks anything up at night that I am aware of even in strong moonlight.
It wakes up at dawn and shuts down at dusk but I must admit none of the panels are looking at any streetlights.
I have always been suspicious of transformerless inverters, just my age I expect lols but just be careful probing the PV side, treat it as if you are probing the grid!

Best I can do for an all day plot, red is power

[prutser]

Before hooking up the multimeter I just performed some other tests:

Turned off the DC switch       -> display shows AC power 22.7W / PV voltage 38.9V
Disconnected both PV wires  ->  AC power 22.7W / PV voltage 38.9V   ( Goodwe invented the PV less PV power source  )

Picture attached which shows the inverter display with at the left bottom side both unconnected PV inputs.  In this state it does not produce power, but
draws approx. 7.5W from the mains.

When switching off (and on again) the connection to the mains, the inverter remains off (and does not consume mains power) until PV is connected.

[fourtytwo42]

It's not unusual for a GTI to consume a small amount of power from the grid in whats called "night mode" ie no PV power, this normally just powers it's zero-cross detector (1W tops), but some like there pretty LCD's to remain lit or smartphone interface to remain working in which case the "night mode" consumption is higher.

Unfortunately when buying commercial products we are left at the mercy of often inexperienced developers who produce mediocre products, although I have my own inverter my CCTV system is commercial and is riddled with these kind of shortcomings............

[hneve]

I've had a similar setup with solar panels and experienced some odd readings at night as well. It does seem unusual for your panels to generate 20W in nearly dark conditions. When I faced this issue, I also suspected some residual voltage keeping the inverter active.

Checking the PV wires with a multimeter is a good idea. In my case, I found that there was a small amount of stray light from nearby sources, but it was minimal. My inverter sometimes showed small amounts of power generation due to its sensitivity and the way it calculates power.

If you still get unexplained readings after your tests, it might be worth contacting Goodwe support to see if they have any insights. They can provide specific troubleshooting steps for your inverter model.

When I bought my own solar setup, I made sure to get a reliable system. I opted for a kit panouri fotovoltaice 5 kw pret and it has been working well for me. Reliable equipment can help minimize such issues, but troubleshooting with support is often necessary for these peculiar cases.

[boB]

Sometimes it is hard for a MPPT controller or inverter to go to sleep when it is supposed to. It's usually just software. Or maybe yours is just a fluke ?  (not the meter !)  You don't want it to waste energy by shutting down all the time but you don't want it to waste power sitting there "ON" either.

I'm pretty sure that the GoodWe was just lying to you in the dark.   Disconnecting the PV input was the correct thing to do to try and isolate the problem.

boB