What should the PV produce on a cloudy day?

[Northspoon]

I have only had the system a few months but I am disappointed with the PV output on a cloudy day. Should I expect it to be better?

I have 12 Aiko panels (445 W each) with Tigo optimisers on two strings going to a Foxess Hi-5.0-E.G2 inverter and batteries. These PV panels are on a south facing garage roof at a pitch of 36 degrees. The roof area is not shaded after 9am.

Today is cloudy and the time is 1pm but the output is only 224W (4.6%). Any advice appreciated.

[Dave Foster]

This is my total PV today, it's been a mix of cloudy, sunny and very cloudy.

My system has 16 * 400 W panels but face a mix of directions East, South & West and quite a few moments today they were doing ~310 watts

224W is low but a lot depends on the suns elevation and how dense the cloud cover was - My lowest output for an *entire* winters day was 0.43kWh

It's best to look at your trace for the day to see how it is performing across the whole day, can you post that.

[Northspoon]

Silly question.....but how do you get that graph? Is it through the Fox ESS Cloud app? My app only seems to show a different graph.

[Dave Foster]

I was using home assistant, but you can get a similar graph on the Fox cloud website by scrolling to the bottom of the inverter details page you posted and in the drop down menu in the empty graph, choose PV Power and press search

[Northspoon]

Thank you Dave, I didn't know that existed it was so greyed out. Here is todays graph. It looks a bit better than I first thought.

[Dave Foster]

Thank you Dave, I didn't know that existed it was so greyed out. Here is todays graph. It looks a bit better than I first thought.

How does that compare with yesterday ? (i’m assuming it was as sunny where you are located as it was in the North West)

Update, it’s gone so cloudy now i’m down to 122 watts

[Northspoon]

I am in the South East where it has been overcast for several days.

I really don't know what to expect from a potential 5kW array on a dull day this time of year. I am on an Economy 7 tariff and so far, since the installation in May this year, I have only used the grid on the cheaper rate, using the battery and solar during the day rate period.

[reef]

We did 7.6kWh today with 9.42kW of panels.

Trust me it gets worse. We did 0.08kW on 2nd January this year (admittedly with only 4.8kW of panels back then, but still!). We had a peak of about 50 watts that day!

I've managed 55.2kWh on a good day in May but only 88kWh all month last December.

The dark months can be dire!

[Northspoon]

Thank you, I guess I was expecting too much of our PV system. On a good sunny day in July we were getting close to 5kWh at mid-day.

[calum]

Thick low cloud will really hurt solar output; overcast-yet-bright days can be surprisingly good. Over time you get a feel for it, weirdly.

[davidwf15]

also experiencing ridiculously low output on anything but bright sunny days.....
we have 14 x 475W Aiko panels, now 6 months old, all facing south with no shading whatsoever....on a bright sunny day we see upwards of 6.5kW (it has even exceeded the 6.65kwP figure showing an incredible 7.4kW!!) but on even a slightly cloudy day we are lucky to see over 400W - this from 14 of the latest high tech panels !!.....but a neighbour who has 10 x 250W panels that are about 15 years old sees well over 1.4kW
So are the panels just not as good in low light ???

[MaterialBarracuda48]

You have to look at the longer term picture with solar.
I was quoted an annual production figure of 5182kWh from a 6.16kWp system.

In just 9 months of 2025, I produced 5700kWh.
You have to remember that solar production isn't a sprint, but a marathon.

YTD for 2026 I have produced 5040kWh, which is good considering I had scaffolding up for several weeks during the Summer peak generation period.

[davidwf15]

Hmmm
....our system went live in April with a PV prediction of 6300kWh ......5 months later we have so far produced a whopping 5700kWh !!
I fully appreciate the winter months won't produce anywhere near as much but was really questioning why, with only light cloud and plenty of visible sun, our system was producing less than 1/3rd of our neighbours 15 year old much lower spec (10 × 250W panels) system....

[MaterialBarracuda48]

That's really good production you have so far, I don't know why the older panels seem to produce better in low light.

Perhaps someone knows why they seem better in low light, I guess the newer panels can peak higher, like over 500W, so it's swings and roundabouts.