Interesting phenomena

[hautions11]

In the winter, my panels get filtered sun through some leafless trees to the south. What I have noticed is a big difference between clear sunshine days and days with filtered sun. On the filtered sun days I consistently pull a couple of KWH's more then the clear days. It must have something to do with sharp shadows crossing the panels on clear days. Has anyone ever seen this kind of output change, or any other ideas why I see this kind of difference?

 

[Andrewr05]

Look up "edge of cloud effect", that may be what's happening.
⠀

 

[hautions11]

Thanks. I read a few posts on edge of cloud affect and it appears to be a relatively short term effect. What I see is a consistent all day difference in output.

 

[Kiwi2000]

Yes if your panels are near a lot of trees, you could generate more on a slightly cloudy day than on a clear sunny day.

The light on a cloudy day is defuse and comes from multiple directions rather than just from the sun itself on a sunny day. A single shadow over a panel can kill a lot of production. The days of thin cloud don't produce as many shadows because the light is defuse.

 

[hautions11]

Makes sense, thanks for the input!

 

[seneysolar]

Compare the temperature of the panels in direct sunlight vs cloudy. As temperature increases, output decreases slightly even when air is cool.

Winter to summer is usually drastic because of this

 

[wattmatters]

Yes if your panels are near a lot of trees, you could generate more on a slightly cloudy day than on a clear sunny day.

The light on a cloudy day is defuse and comes from multiple directions rather than just from the sun itself on a sunny day. A single shadow over a panel can kill a lot of production. The days of thin cloud don't produce as many shadows because the light is defuse.

This, it's pretty common for set ups which experience extended periods of tree/leaf/branch shading - cloudy days often result in more production. Nothing like the output from an unshaded array on a sunny day but the diffuse light helps if otherwise the array was going get some "hard shade".

 

[hautions11]

Thanks guys, The sun is a little higher in the sky now and I am pulling 2-3 KW per hour and my shading is a lot less pronounced. I have gone from 5-6 KWH's in a day to 10 or 12. I only installed this stuff mid Jan of this year, so just learning.

 

[wattmatters]

Thanks guys, The sun is a little higher in the sky now and I am pulling 2-3 KW per hour and my shading is a lot less pronounced. I have gone from 5-6 KWH's in a day to 10 or 12. I only installed this stuff mid Jan of this year, so just learning.

It's good that you are observant enough to notice these things. It will stand you in good stead to notice if something out of the ordinary occurs in future.

 

[Bop]

Compare the temperature of the panels in direct sunlight vs cloudy. As temperature increases, output decreases slightly even when air is cool.

Winter to summer is usually drastic because of this

Where I live in Australia- my peak production times are spring and autumn, winter is down obviously, but so is summer- on hot days when the air temps are over 40C (100F plus) and the panels are running at a measured 80C plus (black panels in the summer sun get hot- who'd a thunk it lol) my panels drop from their rated 250W each down to under 200w each- I lose 20% of my arrays output- just when the loads are highest (I wanna run the A/C dammit...)

 

[BarracudaBob]

This, it's pretty common for set ups which experience extended periods of tree/leaf/branch shading - cloudy days often result in more production. Nothing like the output from an unshaded array on a sunny day but the diffuse light helps if otherwise the array was going get some "hard shade".

I had a similar experience today. It was a record high PV capture day even though there was a veil like upper level light cloud cover. After reading this post I looked it up: Cirrostratus Clouds: Pale, Veil-like Layer. 18.4K on a 3.66K array with zero interruptions. It would have kept going but batteries were at 99% with little loads. Time to buy a Lotto Ticket!

 

[wattmatters]

Where I live in Australia- my peak production times are spring and autumn, winter is down obviously, but so is summer- on hot days when the air temps are over 40C (100F plus) and the panels are running at a measured 80C plus (black panels in the summer sun get hot- who'd a thunk it lol) my panels drop from their rated 250W each down to under 200w each- I lose 20% of my arrays output- just when the loads are highest (I wanna run the A/C dammit...)

We no doubt also get some temperature derating but mainly what kills Summer output for us is the weather - more often in Summer it's rainy/cloudy, while Spring is the driest time of year. Sometimes we can have a dry(ish) summer and when we do production is awesome.



Peak output days for us typically occur in the period a week or so either side of the Summer Solstice. Length of daylight which wins out for us, just needs a clear sunny day in that period. But if the weather in that period is sustained crappy (like Summer of 2020/21) then it'll typically be a clear Spring day that takes out that year's top day.

 

[Bop]

I'm just far enough north and inland we tend to get the 'two seasons a year' weather patterns of the north, rather than the '4 seasons a year' of down south...
Jan to Feb is when we get most of our rainfall (although its been a dry year so far- a couple of major drops, but far below average...)

 

[wattmatters]

I'm just far enough north and inland we tend to get the 'two seasons a year' weather patterns of the north, rather than the '4 seasons a year' of down south...

When I lived in Darwin it seemed like seasons were just wet & dry. But there were various subtle periods during the transitions. But in the dry season you could plan a BBQ years in advance!

 

[BarracudaBob]

I would love to try water cooled irrigation pipe on the back of my ground mount. Heat the pool up and cool down the panels. More KW for the cement pond

 

[ScrotusGobbleBottom]

Thanks guys, The sun is a little higher in the sky now and I am pulling 2-3 KW per hour and my shading is a lot less pronounced. I have gone from 5-6 KWH's in a day to 10 or 12. I only installed this stuff mid Jan of this year, so just learning.

If you installed in Jan. and you are in the northern hemisphere. You are in for some good times! I installed in June and it started great and got shittier and shittier and shittier. Im in my first winter. I learned that the output 2nd week of november to 1st week of feb is as depressing as the temperature is in Wisconsin.

 

[wattmatters]

I installed in June and it started great and got shittier and shittier and shittier.

The power meter keeps an accurate record of your decline.

 

[ScrotusGobbleBottom]

The power meter keeps an accurate record of your decline.

It sure does!