Cloud cover

Hi all, I'm curious to hear from those who have had PV installed for at least 9 months really. When you get thick cloud cover in the summer, what kind of generation do you get? At the moment it is cloudy here (full light grey sky) and my 4.38kW panels are generating around 150W, whereas at the same point on a clear sunny day I'd be getting about 1.3kW. So I'm down roughly 90% on a cloudy day. Would you say that is roughly the same in summer too?

While I do not remember a cloud summer day's PV data looking back at say august my worst PV day was 6.98kw from my 7.02kw array. My worst day in December was 0.5kw so I would say no, cloudy Summer days will produce more. The sun is lower this time of year and without that direct line onto the panel they perform worse. My best day in August was 32.98kw, best day in December 5.25kw

THALL That is what I was hoping to hear. My best December day (10th) generated 6.21kW and worst was 0.2kW. I'm looking forward to the summer even more now! Ha!

chris_p Your installer should have provided you with a generation estimate. I have now had 3 PV systems installed and found the estimates to be close enough to give you an idea of generation. There are also some calculators online that will give you an idea if you know size of your pv system and the direction it faces. I might have 7.02kw of panels but those are split over an East West roof. If your 4.38kw face south or close to it your system will generate more than mine. South is best :-)

THALL I received an estimate from Eon of 4,100 kWh a year. We are South-West facing (about 240 degrees) so should be pretty good. I know I'm being impatient and should just wait to see what happens, nothing I can do to change anything about the system or the other factors 😆

Should you be bored enough here’s every days PV output of last year (not one for mobile)
2021
Has to be very very bleak in summer to get near Dec/Jan type outputs.

hoggy That is fascinating, thank you. Do you make your site available for others to replicate for their own systems?

chris_p Not as such, albeit it's just Wordpress + a Javasript charting library (AMCharts). It does rely on a lot of data fetching/processing going on at home first to make it all play nice (and take out data i don't want shared.)

I did start a standalone project that I'm working on here if that helps?

Hi all

Hope you are all well. I'm quite new to this, so appologies in advance. I just had solar installed a few days ago. It hasn't been the best weather in Scotland the last few days to test this.

I'm hope someone could give me a few expectation checks from what I've been seeing. I just want to check that it's basically working okay, just a case of waiting for a clear sunny day to really give it a good run.

I have:
6.2kw system (16 panels x 390W) - Split East (6 panels 2.3kw) / West (10 panels (1 panel slight corner shaded due to dorma window) 3.9kw)
Panel Spec Trina Verex S 390W (33.8V 11.54A)
Configured in 2 strings

Figures I've currently see in the Givenergy stats for output are:

Day 1 - 4.97kWh (Weather - Part sunny, cloudy and then hale) - 04/02/2022
Day 2 - 1.70kWh (Weather - Full overcast cloud and tipping down all day) - 05/02/2022

Look about right?

Also, looking at the output volts and amps for the days above:

Volts look solid (panel volts added in a string)
6 panel string = 202V
10 panel string = 338V

It's the amps I'm a bit concerned about (max in a string config should be 11.5A (as per the panel spec and string config)
I've only been seeing:

Avg 3A - East Array (6 panels) - (Weather - Part sunny, cloudy and then hale) - 04/02/2022
Avg 1.5A - West Array (10 panels) - (Weather - Part sunny, cloudy and then hale) - 04/02/2022

Avg 0.5A - East Array (6 panels) - (Weather - Full overcast cloud and tipping down all day) - 05/02/2022
Avg 0.75A - West Array (10 panels) - (Weather - Full overcast cloud and tipping down all day) - 05/02/2022

Is this just due to the really bad weather and cloud or something not right?

Thanks all

It’s the weather.
I had mine installed back on December 20th. And had a total of 7kwh generated in December. 60 in January and 13 so far in February.
I have 6 panels south south west, 6 panels west west north 395w each.
Best day was the other day with a total of 6.2kWh generated.

Cloud kills production too.

So I wouldn’t worry too much yet. Looks pretty normal in my limited experience.

I was watching my live data the other day and my southern facing string did peak at just over 2kw.

Thanks @anglefire . Makes me feel better. Good to know, I'll just wait and monitor. I was a little worried that the part shade at the bottom of one of the panels in the 10 array was impacting adversely. Too much YouTube and mixed messages in that area ;-) I'll just give it the time and monitor my setup.

Thanks again

Shade on one panel will reduce the performance of all panels unless there is an additional compensated module on the panels to effectively take the shaded module out of circuit.
I have a big tree in a neighbours garden that shades the panels from about 10:30 to 12:30 - though is reducing slightly as the time progresses. And I have some trees a bit further around that also affect it a little bit from about 2:30 onwards but to a much lesser effect. I calculate they will be out of the equation by the end of the month or thereabouts.
So it could be having an effect.
You have to be a bit philosophical at this time of year I think. Unless you a have perfect view of the sun you are going to have some performance degradation.

Just for a spot of comparison, 6kwp, south facing array and I have shading from my neighbours roof that impacts the lower string for most of daylight bar about 3 hours based on looking at shadows yesterday. The shading hits all of the panels at various points but I have half cut panels so it does reduce the impact of that somewhat.

Yesterday in direct sunlight with no shading I saw a peak generation value of 4.2kw, dropped down to about 500w around 1330 due to cloud cover. Total for the day was 11kwh.

Overcast and generally rubbish weather today, I'll be surprised to see anything over 2kwh total for the day.

One other factor I have noticed is that in 'winter' conditions the panels are often wet from rain or dew first thing, and that reduces output until the panels 'dry out'.

Also, during 'winter' when the sun is low, my top row of panels start producing before the lower rows, even though the lower rows are not in shade. (My PV inverter is a SolarEdge with optimisers, so overall output is 'sum of panels' rather than 'minimum of panels x no of panels').

Hi all just to add that of course in winter there are shorter days and the sun only reaches 22 degrees above the horizon in the midlands at the moment. When the azimuth is 180 at the solar noon 12.20 I’m getting 5.2 kw from 6kw from my south facing system on a cloudless day. Maybe 600watts in heavy cloud. Interesting to note that I only have a 5kw inverter but as it supports dc to dc solar to battery the 0.2 does not count.

My conclusion is that cloud cover is much more important than season, at least in terms of peak output. Obviously the longer summer days will generate more overall.

I think part of this effect is that PV panels generate more voltage in cold weather than when they are hot, so a cool sunny day is ideal. Will be interesting at the end of March when the sun ☀️ reaches 40 degrees to the horizon as this is my roof angle. Sunny day will max out but presumably cloudy days would be better.

Thanks all. I really appreciate your comments. I have the Trina Verex S 390W (Trina Verex S 390W (TSM-DE09.05), some sites show them as half cut and some 1/3 cell cut (no idea what this means, compared to half cut).
https://www.memodo-shop.com/trina-390-tsm-de09-05-vertex-s-black
https://solarshop.baywa-re.lu/Trina-Solar-Vertex-S-390W-Half-31-018070

The object causing my shade is a back dormer window. It's just casting a shade over half of one of the ten panels in that array.

Should have mentioned, my inverter is the GivEnergy 5kW Hybrid

Your best bet is to compare to a solar system of similar orientation, angle and size near-ish to you - try looking on pvoutput.org. Every array will be a little different - but find one similar and it can be a good approximation.

GrahamRead Thanks

GrahamRead Just been playing about on that pvoutput.org site. It's great, exactly what the info to compare against. Thanks for that again. I'm trying to work out how to automatically upload my Givenergy inverter stats to it.

Anyone have any help or done this already?

steve Yes and no. I do upload my stats to it - in fact have been since 2012; but I take my solar readings via bluetooth direct from the Solar inverter not the givenergy inverter / site stats. I use a third party programme to log the readings to a database and then it also takes the readings and posts them to pvoutput site every 5 minutes. Running on a raspberrypi zero.

I don't know if anyone has written anything more generic. The pvoutput API specification is here: https://pvoutput.org/help/api_specification.html

I can’t find anything local to me - though I’m using my phone to look at the site at the moment as we are on holiday.

GrahamRead So should be possible to create a script that pulls the GivEnergy API data and posts it through to pvoutput.org do you think? I have a limited understanding of this kind of thing (used APIs a few times in different systems with scripts but by no means an expert).

chris_p should be pretty doable yes using a python script - or similar.