www.piclist.com/techref/index.htm?key=paralleling+panels

BY : RussellMc email (remove spam text)

Here's a (rough) worked example on a real product

Panel here

www.mitsubishielectricsolar.com/images/uploads/documents/specs/MLU_spec_sheet_250W_255W.pdf

Graphed result here

dl.dropboxusercontent.com/u/30808964/PV%20panel%20mitsubishi%20V43.jpg

1362 x 1544 resolution.

____________________

200 x 227 version

[image: Inline images 1]

____________________________

This is only at 100 90 80 70% full sun but shows what happens.

Green circles show optimum and paralleled current at the selected light

leve.

V is set to Vmp at full power as before.

IF I did it right then results are "interesting".

900 W/m^2 loses little

800 loses rather more - about say 0.2/6.3 or about a minimal 3 %

BUT 700 W/m^2 loses LESS than 800 W/m^2.

Their lines or mine may be wrong.

Method.

Drop vertical from peak power point on power-V curve to relevant V-I curve.

This is mpp for that % insolation.

Draw line horizontal left to show optimum I loaded.

For 100% curve draw line (red) vertically downward to x axis.

This is Vmp at 100% light.

>From intersection of red line and white VI lines draw horizontal lines

(thin red) to Y axis to get Ixx at Vmp100.

Compare differnces of related black and red lines.

HOWEVER - just realised - just looking where the vertical red line

intersects the CYANish power-V curves shows how much loss you get - you can

see peak power at x% insolation and off-peak power when paralleled.

Clear and easy.

AND you can see that the 800 W/m^2 curve loses more power than the 700

W/m^2 one does (!)

SO

Simple method (Agh!)

Draw line vertical from power-V curve for 100% sun to X axis.

Intercepts with other power-V curves show power loss in this case.

QED.

E&OE.

___________________

On 28 April 2016 at 20:52, RussellMc <apptechnzRemoveMEEraseMEgmail.com> wrote:

> On 28 April 2016 at 19:33, Justin Richards <spamBeGonejustin.richards.....spamBeGonegmail.com>

> wrote:

>

>> Does this imply that two separate arrays, one facing East the other West

>> (due to limited roof realestate) could be connected in parrallel without

>> the need for a dual tracking inverter with only a small performance hit.

>>

>> Sort of, maybe.

> Close to "yes in many cases"

>

> If part of a panel becomes shaded then either

> - the max current for all cells in the same series string is the current

> that the shaded cell generates

> - or if the shaded cell has protection diodes then for N cells in series

> and 1 shaded cells thyen

> current max is as before but

> Vpanel_now = Vpanel x n/(n-1) - 1_diode_drop

>

> For panels illuminated evenly but at 2 different levels.

>

> Working through my stack exchange answer, for 100% and xx% illuminations,

> down to about xx >= 50% it looks fairly benign.

> For ery low xx it can still be remarkably good.

> In my 2nd examples, for 20% insolation the 20% panel makes 79% of the

> current it would at optimum but at aboyt 43/39ths the voltage so power drop

> is

> 79% x 43/39 = 87% of the power it would otherwise make.

>

> This is if the 100% panel still works at the old MPP.

> Odds are the combination has a different Vmp and the end result will be

> BETTER than calculated above.

>

> As xx insolation falls there comes a point that Voc is <= the operating

> voltage of the 1st panel and you get nothing.

> In my SE answer that occurs at about 5% insolation (bottom line shown is

> 10%) so you don't lose much.

>

>

> Russell

>

>

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