Less power than expected- is this connected to negative power listed for PV2 in Real-time Device Info stats?

[PurplePooka]

Hi,

We've just had solar installed on a flat roof. 5x 450w panels with a Fox ESS EP6 battery and H1 inverter. 40 degrees west of South facing and 20 degree tilt of panels. No overshadowing except for the scaffolding that is still up from installation. They are in two rows, a row of three and a row of two.

The design from the installer predicted an average of 6.5 kw/h per day at this time of year (April), and in the four days since installation we have had four perfect days of almost full sunshine, though not too hot. This suggests we should have been producing above average power, but on most days it has been below this prediction, around 5.5 kw/h per day on average.

I've checked the readings for the inverter on the app, and I'll admit I don't really know what I'm looking for but I did think the readings below were strange.



I am assuming PV1 is the row of 3 panels and PV2 is the row of 2 - shouldn't PV2 have roughtly 2/3 the voltage of PV1, rather than a tiny fraction? PV2 also consistently shows 0 current and a negative power.

Is this our problem, and if so, what can we do?

Many thanks to anyone who can help!

[Dave Foster]

If you only have 5 panels, then they will all be connected to a single string - it won't function with 2 / 3 split on 2 strings, the small voltage you see on PV2 is simply an open circuit pickup.

A lot will depend on your panel direction, elevation and of course weather - even a clear day can have high cloud that will affect the solar and whilst elevation is improving it will be another month or 2 before that is at best.

As the scaffolding is still up, even a modest pole can cast a shadow that will affect a panel and as they are connected in series that panel can have a throttling affect on all panels - give it some time, get the scaffold down and then review.

[PurplePooka]

Thanks so much for your quick reply, Dave!
That is interesting to hear about the high cloud - some days that seemed a little cloudier have produced more energy, and earlier in the day, so that's a good explanation.
I also didn't realise that shadow on one panel had a strangling effect on others in the string - that's interesting, and does reassure me a little that the panels will work better when the scaffolding is down. The only trouble with this, of course, is that once the scaffolding is down, it will be a lot more difficult and expensive to make any changes...
By "elevation", do you mean the height of the sun/time of year? The information I was looking at from the installer did take this into account, so the lower production was against the predicted daily average for April.
I'm hoping I can get them to install another panel before they take the scaffold down, as their design assumed there would only be room for 5, but now that they're up it's obvious that there is a gap where the frame could be extended for a sixth. I'm pretty sure that would make a big difference for us.
Thanks for all your help!

[Dave Foster]

Yes elevation is the angle of the sun during the day throughout the year, this is the elevation change for my location through the year,

With higher elevations shadow and azimuth effects (and atmospheric scattering) reduce which will increase the irradiance, but as you mentioned increases in temperature will reduce the panels efficiency and so the sweet spot is slightly different for each setup - For my system the ideal day is a clear blue sky in mid May but with a cold ambient temperature.

High cloud on a clear day tends to reduce solar power, but ironically with white Cumulus clouds you can get something called Cloud Edge effect where the sides of the cloud reflect sunlight, increasing the total irradiance to all panels (much like a magnifying glass).

If you have the option to add another panel it makes sense to do it whilst the scaffold is up, you’ll always regret it later and an extra panel will help on the days where solar isn’t very strong.