RE: Re: Solar PV

[Marcus Warrington <marcus.warrington@xxxxxxxxxx>]

Welcome to the wonderful world of micro generation !

If you had yours fitted last week and have seen 4014W of generation then
your definitely nowhere near Manchester as we seem to have had pretty much
constant cloud cover since mine was installed :)

Regarding the shading and strings, I agree with you. The design should
restrict the shading to the smaller string. As you have seen, even if a
single cell in a solar panel has shading on it then the whole string will
be affected.  They don't mention what software they've used but I suspect
its simply specifies the number of panels to put on each string (i.e. 12
and 4) and not which string should be in the shadow zone. It will be
choosing the number of panels on each string based on their combined
voltages and the range of voltages that the inverter can process.

I'm not sure they will be able to alter which panels are on which strings
from inside the roof because the panels are wired in series so you will
only have 2 wires for each string (+'ve and -'ve) inside the roof. Which
panels are grouped on those wires is determined by how the wire joins up
from one panel to the next on the roof , under the panel.. hence the need
to remove the panels to do this.

Marcus

From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of Simon
H
Sent: 30 August 2011 11:52
To: ukha_d@xxxxxxx
Subject: Re: [ukha_d] Re: Solar PV



My first question posted on this forum after many years: be gentle with me!

My solar PV was installed last week, and consists of 16 off Sanyo HIT
250W panels, in two strings (12 and 4). The inverter is an Aurora 3600
(3.6KW) which was specified due to the separate strings, but I
understand to be a very good unit. A small amount of chimney shading
during a small part of the day was factored into the design, hence part
of the reason for two strings.

Thus far I am happy, and have seen 4014W once or twice indicated under
optimal conditions. Oh how the Aurora hums!

However, I have seen one thing I have had cause to question: since I
cannot peel my eyes away from the inverter readout I noticed the main
array output drop to 500W, when the smaller array was managing 1024W. I
rushed out to see that the chimney was shading a small part of one panel
on the main array. This effect lasted a few minutes and then passed.

Conclusion was that shading affects output far more than I imagined, and
caused me to question why the strings had been designed in that
configuration. Surely the design should make the smaller string the one
most affected? Answer from the installer: it's the way the software
spits it out and we are often surprised ourselves.

I don't find this satisfactory. As the angle of incidence changes over
the year, shading will become more of a factor. The installer has
stated that to change this will mean more scaffolding and panels off to
change the cable layout. There was me thinking they could just chop and
join the cables in the loft space. On that point, they were going to
use 4mm cables throughout, but based on what I have read here, I
persuaded them to use 6mm.

I can only monitor the output for now to see what's what, but I am also
nervous about forcing them into changing the layout only to find they
were right all along! Can you see my dilemma?

Thoughts, comments, and suggestions welcome.

Cheers,

Simon H

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