How much does "Uniform Shading" affect array output?

stereoman405

Just got back from our cabin from a 'solar planning trip' and have a few concerns now. (Cabin is at roughly at 48.5 degrees latitude.)

Our due south facing roof gets a lot of direct sun exposure during the summer months, but during this time of year (Feb) it gets very little if any direct sunlight. I was watching it pretty closely for three days and it seems like only 10% of the roof ever got solid light, and that was for 30 minutes. The rest of the time it was pretty diffuse coming through the trees only marginally. The ambient light levels were decent, just not direct.

Assuming all the panels are uniformly getting the same lack of direct light (no spotty shading), do you still get any kind of current front them? Or is it so negligible that you can barely count it? I have 4 REC 210's that I was planning on using. Is there a % I can plan on?

mike95490

Re: How much does "Uniform Shading" affect array output?

in rain, with clouds, i'd get 300 W froma 4.5 KE array. Bright sun is best, anything else is is less, all depends. Sometimes hazey skys give better all day harvest, no peaks, but a steady illumination from the haze really cranks out the power

niel

Re: How much does "Uniform Shading" affect array output?

if you are just float charging the batteries then no problem, but if you use power from the batteries then the batteries will not recoup that which was used. i would guess a small generator for visits during the winter months for any needed power and to top off the batteries.

stereoman405

Re: How much does "Uniform Shading" affect array output?

niel wrote: »

if you are just float charging the batteries then no problem, but if you use power from the batteries then the batteries will not recoup that which was used. i would guess a small generator for visits during the winter months for any needed power and to top off the batteries.

That's kind of what I was hoping for. The cabin is grid tied so I will have a grid charger on top of the panels to keep them floated, but power does go out up there so it would be nice to have the batteries staying healthy regardless. I also figure if even 1-2 amps made it through I could still use some lighting without hitting the batteries too hard.

For extended use I do have an eu2000 I can haul up there, but that is a hassle so I usually leave it at home.

westbranch

Re: How much does "Uniform Shading" affect array output?

Cab you remove any of the trees to get a blast of full sun?

EJ

stereoman405

Re: How much does "Uniform Shading" affect array output?

westbranch wrote: »

Cab you remove any of the trees to get a blast of full sun?

EJ

I MIGHT be able to do a little thinning as some of the trees are the neighbors. This would make it so I would be getting splotches of direct light. I just wasn't just if splotchy was better then consistently shaded.

Would running more parallel strings instead of series strings help with the low lights times?

drees

Re: How much does "Uniform Shading" affect array output?

stereoman405 wrote: »

I just wasn't just if splotchy was better then consistently shaded.

The more direct light you can get on the panels, the better. Micro-inverters might be a good fit for your application.

BB.

Re: How much does "Uniform Shading" affect array output?

I am not sure that there is much you can do to make the output better... If you have several strings of panels (series/parallel connected) -- put that one series string in the full light.

In reality, the energy from solar panels is directly proportional to the amount of sunlight hitting the panels. In shade but with full exposure to sky glow--you probably will not even get 1% of your panel's rated output.

If you have a solar panel--you can do a quick experiment. Set your meter to 10 AMP scale and connect it to the solar panel. In full sun, you may read 5 amps. In shade, you may read 0.05 amps... Solar panels are very linear in current output to the amount of energy hitting the panel.

You could even do this measurement with a small solar panel from almost anything (yard light cell, etc.). Just measure the short circuit current in full sun and shade at the cabin (or similar shade at home).

Also, if the trees are not yet at full height--you may loose more and more sun outside of winter as the trees continue to grow...

-Bill

mlail

Re: How much does "Uniform Shading" affect array output?

Is there a better area that gets more sun exposure? Maybe the West facing roof. The word cabin usually means lots of trees and no direct sun.

Also what about using a solar tracker (if there is enough space and sun in the yard).

You might want to consider augmenting what you have with other panels? I have read where others will add 2-4 or so panels on a pole mount, somewhere in the property. This give them the additional power needed during those critical times.

I'm fairly new to PV so these guys would know better but maybe my 2 cents worth can help!

westbranch

Re: How much does "Uniform Shading" affect array output?

If there are any deciduous trees , in summer you are going to have a lot less direct or even shaded light...that said you may be pleasantly surprised at how much improvement you get from removing just one tree. If you can get a big friend to thump the trees for you, about 5 feet up, you can use your shoulder, while you watch the shade pattern, do it around noon. Pick the most offending tree and remove it first. As said before, when having fun, repeat as necessary..
Yes pruning will help a bit but then you get the stem shadow...
Concur with the pole mount idea, lets you pick the best location rather than the ok roof siting...

hth
ej

add: I just remembered that is you have an Aspen (Poplar) in the mix, at this time of year the shadows thrown by the small branches will drop your output greatly, even though you may not 'really' see a shadow line.. Do a before and after reading on the amps you get if this is the situation (Aspen) you will be surprised...

BB.

Re: How much does "Uniform Shading" affect array output?

Is it possible to share a "solar array" site on his property and run some "high voltage" wires to your cabin?

Perhaps you can help him and make a joint project out of it and get him wired up for power too.

-Bill

stereoman405

Re: How much does "Uniform Shading" affect array output?

mlail wrote: »

...The word cabin usually means lots of trees and no direct sun.

You got that right.

Unfortunately fitting a pole somewhere else in the yard won't work very well either. We're on .3 acres with neighbors pretty close in either direction, so even if we completely clear cut the entire property their tree will still cast a pretty good shadow. our cabin is a two story a-frame so it's already higher than any poles can get easily.

Just had a thought, two questions here:

1. Can I assume that the sun will get higher in the sky as we transition to summer? The tree tops are just barely blocking it now.

2. Do they make a 'peak mount' that could potentially put the panels up beyond the peak of the cabin? Seems like as soon as you go up even a few more inches the exposure gets much better.

stereoman405

Re: How much does "Uniform Shading" affect array output?

Here's a few pics for reference:

East Side


South Side
Light was directly hitting the top right (east) corner here the day before.


South Side 2


West Side


NOTE: This was the ambient lighting around 3:00pm on a very overcast day.

westbranch

Re: How much does "Uniform Shading" affect array output?

Q 1 - yes and as we all know we get lots more sun as the sun rises higher and sets higher (further N) as we approach the summer solstice.

Q 2 ?? others may be able to help on this

Can you attach a pole to the end of the Cabin to catch that pocket of light??

Eric

ps - not a lot of snow this year or is that normal for your site?