Slow starting solar- any ideas why?

JKenH · 15 September 2018 at 5:22PM

I am lucky enough to be able to look at a neighbouring solar installation's output on line to give me a yardstick for my own panel performance. What I have noticed is the other system starts up significantly earlier than mine. It was an hour this morning and that is despite me having both east and west facing panels whereas my neighbour’s is much closer to south.

I am satisfied it is not due to shading as today was totally overcast. What I do see is the neighbour’s installation builds up very slowly and mine starts quickly. For instance today I had nothing until 8.00 am then instantly it goes up to 300 watts or so on the Moixa Dashboard. It is almost as though the panels have to reach a certain output before the inverters start working.

The inverters are Sofar Solar.

Does anyone have similar experience or any explanation for me please?

Martyn1981 · 15 September 2018 at 5:31PM

If it helps my monitors seem to show the inverters switching on at around 30-40W, and switch off around 15-20W.

This is probably a red herring, but how does the Moxia get its info, does it talk to the inverters or is it from a clamp style meter on the generation cable, as they can be very unreliable till around 1A, so say 200W+.

JKenH · 15 September 2018 at 6:16PM

Thanks Mart, I can always rely on you for some good technical advice.

Moixa gets its info from a clamp. I agree the figures are unreliable and do also suffer interference from the consumption. Currently Moixa is showing 400 watts while my inverters show 250 watts.

Once my panels were running this morning I was seeing between 270 and 420 watts on Moixa. At 08.31 I was seeing about 350 watts on Moixa when the inverters were showing 190 watts (split 100 west/90 east) and my neighbour’s 127 watts from his 4 kwp set up. Neighbour’s was 104 watts at 8am when mine were starting up so pro rata my inverters would have been putting out just over 150 watts. Bearing in mind I have 2 inverters that would work out about 75 watts each to start up. Does that sound as though it is too high?

You may remember that my system trips out as it starts up. This morning unusually it tripped out a second time about 8 minutes after I had restarted it. Do you think there is any connection between the sudden start up and the tripping out?

JKenH · 15 September 2018 at 8:42PM

I have found some info online about the Sofar 3680 inverter and it says the start up input voltage is 100 volt +/- 5v but I don’t know how that relates to my panels’ output (12 x 300w panels on the east roof). Can anyone comment please?

This is the label on the panels.

https://www.dropbox.com/s/z1cz55914gslp44/IMG_3320.jpg?dl=0

Martyn1981 · 16 September 2018 at 6:54AM

I'm afraid my knowledge is all used up, I just tend to remember past incidents and can attempt to relate them. Looks like you need someone with leccy skills.

Zarch · 16 September 2018 at 8:24AM

I do remember a conversation with a prospective installer who did say something about the inverter needing a minimum amount of generation to fire up the inverter. Can't remember much more than that though, sorry.

Is it worth contacting your installer? Or Sofar direct?

jimjames · 16 September 2018 at 10:52AM

JKenH wrote: »

Thanks Mart, I can always rely on you for some good technical advice.

Moixa gets its info from a clamp. I agree the figures are unreliable and do also suffer interference from the consumption. Currently Moixa is showing 400 watts while my inverters show 250 watts.

If that's consistent then the Moixa is 150W above the actual output so 300W on that is 150W on inverter which might be about the minium output and limit of detection for the moixa. So it's probably better to look at output from inverter itself.

My panels are south facing with no shading and start at 7am at the moment (SE England) but are under 100W until 8am.

Heedtheadvice · 16 September 2018 at 12:41PM

found some info online about the Sofar 3680 inverter and it says the start up input voltage is 100 volt +/- 5v but I don’t know how that relates to my panels’ output (12 x 300w panels on the east roof). Can anyone comment please?

As you have written your inverter will start to generate at 100v input from the panels. So critically generation start will be when your generation reaches that figure. Similarly your neighbours (same model of inverter?).
That voltage is dependant (mainly) upon received radiation at the panels plus their ability to turn that into a pv generated voltage. Several things come into play such as orientation, angle of panels, cleanliness, shading (even in cloudy conditions) number and type of panels, configuratuion (number of strings) and efficiency of conversion from solar to voltage -especially at low levels of irradiation for start up.
So you need to compare like with like and try and find the generation efficiency curves of both sets of panels for starters.
As suggested previously you also need to ignore the readings except those actual ones from the inverter rather than the innacurate (at low levels) from that particular clamp monitor setup!

JKenH · 16 September 2018 at 8:43PM

Heedtheadvice wrote: »

As you have written your inverter will start to generate at 100v input from the panels. So critically generation start will be when your generation reaches that figure. Similarly your neighbours (same model of inverter?).
That voltage is dependant (mainly) upon received radiation at the panels plus their ability to turn that into a pv generated voltage. Several things come into play such as orientation, angle of panels, cleanliness, shading (even in cloudy conditions) number and type of panels, configuratuion (number of strings) and efficiency of conversion from solar to voltage -especially at low levels of irradiation for start up.
So you need to compare like with like and try and find the generation efficiency curves of both sets of panels for starters.
As suggested previously you also need to ignore the readings except those actual ones from the inverter rather than the innacurate (at low levels) from that particular clamp monitor setup!

Thank you for your input.

Is 100v start up good or bad with 12 panels on one string? Would I have been better with a different start up voltage?

How do I know when generation reaches 100v? I think my panels switch on at about 75watts (inverter figures not clamps) so I am looking for 0.75 amps. So I need somehow to know when the panels are producing 100v or 0.75 amps? How would I establish that?

You have suggested a number of other factors that come in to play. The orientation of my panels is 80 (almost east) as opposed to 165 (nearly south) for the nearby property and the inclination of my panels is 39* compared to 35*. My panels are clean, only 2 months old. I have 12 300 watt panels on the east elevation served by one Sofar Solar 3680 inverter (so presumably one string), as opposed to 16 250 watt 8.33 Solar on one elevation with a Solaredge inverter. There is currently no shade on my roof at that time of morning.

I don’t have the efficiency figures for either set of panels. I appreciate that a solar specialist would like to have those figures but given that the orientation and inclination of my panels would be more suited to an early morning start up, it still strikes me as odd that with a 6.50am sunrise the neighbour’s panels start up at 7 and mine at 8 on an overcast day. This morning it was still cloudy but bright and the difference was 40 mins.

I am interested by what you say about shade on cloudy days. My own experience on overcast days is that my east and west roofs tend to produce PV pro rata to the number of panels even early morning and late afternoon when one of the roofs would be ‘in shade’

Martyn1981 · 17 September 2018 at 7:39AM

JKenH wrote: »

Thank you for your input.

Is 100v start up good or bad with 12 panels on one string? Would I have been better with a different start up voltage?

I have to say I'm finding all these references to Volts confusing. I'd have thought the V figure is simply to tell you the minimum volts that the system needs to work (not start), and minimum needed for the MPPT(s). So that's for you/installer to know the minimum number of panels needed. Eg is the panels are 30V each, then for 100V you will need a system of 4+ panels.

The voltage should be equal to the volts per panel x no of panels, even on tiny amounts of generation, so perhaps 300-700V but an extremely low amperage giving you say 20W, or 50W etc.

Edit - Just done some checking. My ESE system is showing 90W and 380V. Checking panel specs I should have 5x30V + 13x21.5V = 430V, but some panels are still in shade, and looking at playback they are not all on or staying on yet.

Correction, my system being Solaredge will be the sum of the PO voltages, not the panels. Seems to be at 380-383V regardless of watts.

JKenH · 17 September 2018 at 8:45AM

It’s a very uniform grey sky here this morning. I took a cup of tea up into the loft to wait for the inverters to kick into life - long wait,

My east side panels came on at 8.07 and the west side 30 secs later. When they had settled down ie been on about a minute the east side inverter was showing 90 watts and west side 100 watts, the difference being down to the number of panels.

My neighbours came on at 7.05am - an hour earlier.

Slow starting solar- any ideas why?

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