What do your Solar panels do when....

[Nico13 (Ken)]

When it’s partly cloudy as opposed to a clear blue sky?
To be more specific, I have a 2KW Solar system installed five months back that has consistently produced about 1500W on the instantaneous readout at any one time and the only time I ever saw it go anywhere near the 2000W was the first day it was installed and turned on.
That was up until the recent season change and the sun climbing a little higher in the sky, my Panels are on my shed roof and only at 12deg pitch facing pretty much due North so the lower output through winter could be fully understood.
Now my inverter is located in my shed just above my work bench so I can see what’s happening as I work and at the same time notice the sunny and shaded patches as the clouds drift by.
Now here’s the interesting part, when it’s a clear blue sky not a sign of cloud but at worst a tiny amount of atmospheric haze the panels float along at around the 1500W output.
But when there is broken lower level cloud you know the nice fluffy stuff you tend to see in spring that comes and goes and you can watch it evaporate under the warm sun well then the panels will pump out anything up to the 2000W (equaling the system size) and even a bit over for an instant I saw at one stage and that’s when the sun is shining through that light evaporating cloud.
I know the panels have a diffused glass to help optimise the suns rays but for some reason the additional scattering caused by the light cloud enhances this by what would seem to be at times up to a 25% increase in performance.
Wouldn’t it be great if you could capture that scattering pattern caused by the clouds and design that into your glass on the panels. A big improvement on efficiency could be had.
Anyone got a light ray scatter pattern capturing machine.
Maybe I should be puting a patent on this

[Larryp (Laurie)]

That's interesting, Ken. But I can't explain why-you would think with some cloud, you would get less light falling on the panels

[acropolite (Phil)]

That's normal behaviour, backscatter from the clouds together with light reflected from the ground and back from the clouds cause the increase. It's no accident that the US National Electric Code specifies that solar controllers be rated at 125% of the array output.

[Nico13 (Ken)]

Originally Posted by acropolite

That's normal behaviour, backscatter from the clouds together with light reflected from the ground and back from the clouds cause the increase. It's no accident that the US National Electric Code specifies that solar controllers be rated at 125% of the array output.

Yeh Thats what I reckoned was happening, that's why I wanted the scatter pattern machine

Originally Posted by Larryp

That's interesting, Ken. But I can't explain why-you would think with some cloud, you would get less light falling on the panels

Not less light just the angular difference and reflected as mentioned above

[traveller (Bo)]

Nah, just smokes and mirrors
Bo

[Exfso (Peter)]

My 4.5kw system regularly peaks at over 5.5kw in similar circumstances, wonder what it does to the 5kw Inverter, hopefully it has a built in variation to handle these "Peaks". In mid summer at midday with north facing panels, no cloud, it chugs along at around 4.0kw to 4.2kw. I have noticed on really hot days it drops back a bit, so they obviously don't fancy running too hot.

[Nico13 (Ken)]

Originally Posted by Exfso

My 4.5kw system regularly peaks at over 5.5kw in similar circumstances, wonder what it does to the 5kw Inverter, hopefully it has a built in variation to handle these "Peaks". In mid summer at midday with north facing panels, no cloud, it chugs along at around 4.0kw to 4.2kw. I have noticed on really hot days it drops back a bit, so they obviously don't fancy running too hot.

Yep did see that when doing the research on the systems that they didn't like it too hot, gotta be just nice

[MrB (Simon)]

Originally Posted by Exfso

...
I have noticed on really hot days it drops back a bit, so they obviously don't fancy running too hot.

About two decades ago I came up with an idea to fix that problem.
Basically you build the PV panel on a Solar Hot Water panel, the water cools the PV cells and you get Hot Water. Win-win.
The PV panels might not get hot enough so it's probably more suited as a pre-heater for a smaller separate SHW panel operating as a booster.

I never really gave it much thought since, but a quick search reveals others have thought of it too: http://en.wikipedia.org/wiki/Photovo...olar_collector

[Baddad (Marty)]

Silicon does not like heat. Performance improves at low temperatures quite dramatically. Direct sunlight heats the panels.
While a North aspect is best. East is next, losing 10%, while the West aspect has more heat and is 1- 5% less efficient than East

A small shadow over one cell will reduce that panel output significantly. The cells are in series. One cell resistance goes high and panel output is limited by that cell. So watch for bird droppings.

As Summer comes on the angle of incidence will change. Less reflection off the glass surface. @ 12 degree pitch in Southern Victoria will have significant affect on the efficiency. To improve, a pitch kit will increase output. Be aware not to unplug any DC cables under load. Big arcs and sparks. (carries around 200 - 500volts)

To have it done by qualified techs is expensive and not worth the extra outlay for that extra 500w

Ideally the panels should be positioned so that they are at 90degrees to the sun's rays.

Cheers

[MrB (Simon)]

Originally Posted by Baddad

Be aware not to unplug any DC cables under load. Big arcs and sparks. (carries around 200 - 500volts)

To have it done by qualified techs is expensive and not worth the extra outlay for that extra 500w

Ideally the panels should be positioned so that they are at 90degrees to the sun's rays.

Cheers

I cover the panels with large towels and use cheap plastic table cloth clips(something like this) to hold them there, works great.
Canvas or something similar would work just as well.