How much Seasonable Variation to expect?

[DickiePhitt]

6 weeks ago I had 24 x Sanyo 240w panels and SMA 4000TL fitted to a S facing roof without shade.

For a few days after, the sun shone very occasionally and at these times I regularly saw over 3kw being generated and peaks of 4.2kW on the screen of the Sunny Boy. Daily yields averaged 13.7kw for the 12 last days in August - none of which were particularly lovely days here in Yorkshire - with a couple of peaks around 21kW and the 3 lowest between 3-5kW.

I returned from holiday yesterday expecting that the recent days of wall to wall sunshine would have made for some record-breaking outputs. It was somewhat surprising to find between 16-17kW was generated each of the fine days. Today the generation pattern is identical and the display on the Sunny Boy at no time has been over 3kW.

Simplisticly it looks as though performance in full sunlight has reduced from 4.2kW to 2.9kW in the space of 6 weeks.

This seems excessive (even allowing for lower angle of the sun) and I'm wondering if something on the inverter has changed. The supply meter was changed 2 weeks ago - it was counting up exported units but that is another battle - so the panels and inverter were isolated / reconnected at that time in the proper manner. Only thing I could think of was whether inverter settings had been modified on commissioning and not saved, meaning they had returned to a default.

Is this reduction of the order to be expected? Maybe someone has knowledge of what a 3.84kWp system has been producing in the past few days. Any thoughts appreciated.

 

[IronLiver]

Are the details in your post correct? 24 x 240W panels would be 5.76kW, which does not appear to be compatible with the SB 4000TL. Did you mean 16 panels at 3.84kW?

 

[MorganPVI]

Whats the pitch of the roof? Not that it makes a huge difference.

Commissioned a 4kw system today that is only peaking at 3kw, I put this down to high panels temps and a low angle of Sun @ 900wm2 at midday.

Edit - A 3.76 system generated 16kwh Wednesday, 16.5kwh yesterday and is 15.6kwh as of 16.30 today. peaking at 2700W.

 

[DickiePhitt]

Whoops - yeah its 16 - miscounted, duh. Its a 30 deg roof so fairly optimal I reckon.

Noticed this morning a factor of 3 between the currents of the 2 arrays up to 11am which I think has to be shadow from TV aerial. Just moved it so interested to see if better output tomorrow morning. After 11am both arrays matched exactly at 334v 4.3A

Those numbers posted so far would seem to bear out what I'm getting - what a difference 6 weeks makes.

 

[MorganPVI]

I assume it's arrays of 8 and 8 the only difference is one is shaded by the TV aerial. If so then it's a classical example of the dangers of minor shading.