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diy solar

Solar panels and weather variation

frankz66

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Hi everyone, I can't understand why my panels, 4 from 180w 2s2p on some very cloudy days charge discreetly, while it happens that on some cloudy days, they charge a few watts ...... Does it depend on the radiation that is filtered by the clouds in some contexts or something else? Sorry but I'm still at the first experiences
 
My situation is a good example of your question:

My 200W South-East oriented array starts receiving sun around midday. In sunny days this means I do not produce a single watt until 1PM.
This is partly due to my inverter that requires 10W to inject power to the grid.

In cloudy days I however produce all throughout the day thanks to the irradiation diffraction caused by the clouds; this means I already start producing 15W from 9AM and reach peaks of 40W. The thin clouds disperse light in all directions which allow panels in the shadow to capture more light.

When the clouds are thicker (like during storm) then I will not capture anything.
 
My situation is a good example of your question:

My 200W South-East oriented array starts receiving sun around midday. In sunny days this means I do not produce a single watt until 1PM.
This is partly due to my inverter that requires 10W to inject power to the grid.

In cloudy days I however produce all throughout the day thanks to the irradiation diffraction caused by the clouds; this means I already start producing 15W from 9AM and reach peaks of 40W. The thin clouds disperse light in all directions which allow panels in the shadow to capture more light.

When the clouds are thicker (like during storm) then I will not capture anything.
Hi Jordi, in fact I could install these other two panels not one next to the other, but maybe one east and one west! I don't understand your 10 w or 40 watts .....
 
Hi Jordi, in fact I could install these other two panels not one next to the other, but maybe one east and one west! I don't understand your 10 w or 40 watts .....
My grid-tied inverter requires a PV power of at least 10W to inject AC current to the grid. Below that it does not inject current as it is too low.

40W is my PV array peak power during a cloudy day.

Do not put two solar panels of the same array in different orientations while in series. Read what other have commented about that below.
 
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Do not put two solar panels of the same array in different orientations; result is very low output
Actually, it depends on how different the orientation is. I have one array pointed at 155°, one array pointed at 205°.
These arrays are parallel connected in a combiner box and wired to one mppt.
Their output is just fine.
 

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Actually, it depends on how different the orientation is. I have one array pointed at 155°, one array pointed at 205°.
These arrays are parallel connected in a combiner box and wired to one mppt.
Their output is just fine.
Thank you Tom for posting the photo too. But I wonder: everyone says to place the panels at 30 40 degrees ??
 
Do not put two solar panels of the same array in different orientations; result is very low output. If they are in different arrays, they should have different Solar Charge Regulators like PWM or MPPT.

You can do it if they are in parallel
 
Hi everyone, I can't understand why my panels, 4 from 180w 2s2p on some very cloudy days charge discreetly, while it happens that on some cloudy days, they charge a few watts ...... Does it depend on the radiation that is filtered by the clouds in some contexts or something else? Sorry but I'm still at the first experiences
Three things to consider along with everything else:

1. Your eyes are logarithmic, and what may seem like a bright overcast day to you may actually be quite dark, and what may seem like dark scattered clouds may be quite bright. You'd need a light meter to know for sure - but you already have one - your solar panels, with an appropriate MPPT converter, will match the light level, along with the angle the sun is landing on them.

2. Solar panels are most sensitive to infrared light. While they'll convert all along the visible spectrum, infrared levels will affect them more than visible light levels. Clouds of different types and densities will have an infrared transparency that doesn't match their visible transparency, so some clouds may allow a lot of visible light through and little infrared, or vice versa. One of the biggest factors is whether the cloud has ice in it or not. https://opg.optica.org/josa/abstract.cfm?uri=josa-50-9-876 . Again, what your eyes perceive and what the panels receive may be different.

3. Dirty panels affect the power greatly. If, for instance, you have a month of bright sunny days which result in dust covered panels, then a cloudy day with rain that washes the panels, then a cloudy day that seems darker than the previous day you may find that the seemingly lighter cloudy day produced less energy than the one that seems darker.

These are just a few variables that you would have to track to really understand what's going on - there are many more. It's not a simple problem, and generally it's not worth spending a lot of time on unless you believe there's a significant energy loss and you need to find the cause.
 
Thank you Tom for posting the photo too. But I wonder: everyone says to place the panels at 30 40 degrees ??
Yes, from horizontal.
Two angles at play here. The general tilt from horizontal and where in the sky they are aimed.
So I am in Maryland, USA, and my latitude is 39° north. Therefore, my panels are tilted from horizontal 39°. However the arrays in combination are aimed at 180°.
 
Silicon PV panels favor red-IR end of light spectrum for output current. Blue end of spectrum contributes less to PV power output.

The more water vapor in the path the worse the PV performance. Water vapor red-IR absorption does not always match the apparent visible lighting blockage.

Sun spectral intensity.png
 
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Three things to consider along with everything else:

1. Your eyes are logarithmic, and what may seem like a bright overcast day to you may actually be quite dark, and what may seem like dark scattered clouds may be quite bright. You'd need a light meter to know for sure - but you already have one - your solar panels, with an appropriate MPPT converter, will match the light level, along with the angle the sun is landing on them.

2. Solar panels are most sensitive to infrared light. While they'll convert all along the visible spectrum, infrared levels will affect them more than visible light levels. Clouds of different types and densities will have an infrared transparency that doesn't match their visible transparency, so some clouds may allow a lot of visible light through and little infrared, or vice versa. One of the biggest factors is whether the cloud has ice in it or not. https://opg.optica.org/josa/abstract.cfm?uri=josa-50-9-876 . Again, what your eyes perceive and what the panels receive may be different.

3. Dirty panels affect the power greatly. If, for instance, you have a month of bright sunny days which result in dust covered panels, then a cloudy day with rain that washes the panels, then a cloudy day that seems darker than the previous day you may find that the seemingly lighter cloudy day produced less energy than the one that seems darker.

These are just a few variables that you would have to track to really understand what's going on - there are many more. It's not a simple problem, and generally it's not worth spending a lot of time on unless you believe there's a significant energy loss and you need to find the cause.
Thanks for your technical explanation that I didn't know, except for the dirty panels factor. My panels are in "PERC" technology, they should be more sensitive to infrared. However it is true as you say, in fact I have found it because a few times where the weather conditions seemed more adverse, the production compared to today (only 650 watts towards batteries) was much better. Surely the conditions of the clouds, infrared and type of cloud affects a lot. I do not want to say that if it charges little there is a fault, but the weather condition including UV is not optimal. Thank you
 
Silicon PV panels favor red-IR end of light spectrum for output current. Blue end of spectrum contributes less to PV power output.

The more water vapor in the path the worse the PV performance. Water vapor red-IR absorption does not always match the apparent visible lighting blockage.

View attachment 147344
Hi, and thanks to you too. Clearly I try and strive to understand the reading of the graphs, still too young in PV! However, your technical explanations lead me to learn elements that I didn't know but I could guess. My plant is small, but at the moment enough for my needs. Unfortunately it happens that every time it makes more, I think about how I can improve, making the mistake of not having made a good design. But this is normal for those who in all fields, invest and learn at their own expense. If that hadn't been the case, I wouldn't ask questions around for perplexity and doubts. Anyway, thank you for your help or rather for your information!
 
If you look at the typical solar panel data sheet, it has a single current vs voltage curve for how they behave under "standard conditions". Part of this "standard condition" is temperature, intensity, spectrum, and "directionality" - probably there is a better term for this and perhaps other stuff.

So if any of these conditions varies from "standard conditions", then that curve starts shifting around, most often to be lower and to the left.

Overcast conditions cause a shift in the spectrum, intensity and "directionality", so for instance the Vmp will drop - sometimes considerably.

A charge controller needs the incoming voltage (Vmp ) off of the panels to be higher than the battery voltage.

A PWM controller such as a bogart only needs this to be 1 - 2 volts higher to work.

An MPPT controller needs this to be 5 volts absolute minimum to turn on for the higher end ones, 10 -15 volts for some of the lower end ones. You didn't mention if you battery pack is 12 or 24 volt but if 24 volt this could be a factor.

If you have a low end controller like a renogy rover, they use a lot of power even when not generating any power - so you can literally have solar power being generated, and the controller consumes much of it.

_________

If you are in an area with a lot of overcast, sometimes it makes sense to use poly panels as they can capture this scattered light better (under some conditions. )
 
If you look at the typical solar panel data sheet, it has a single current vs voltage curve for how they behave under "standard conditions". Part of this "standard condition" is temperature, intensity, spectrum, and "directionality" - probably there is a better term for this and perhaps other stuff.

So if any of these conditions varies from "standard conditions", then that curve starts shifting around, most often to be lower and to the left.

Overcast conditions cause a shift in the spectrum, intensity and "directionality", so for instance the Vmp will drop - sometimes considerably.

A charge controller needs the incoming voltage (Vmp ) off of the panels to be higher than the battery voltage.

A PWM controller such as a bogart only needs this to be 1 - 2 volts higher to work.

An MPPT controller needs this to be 5 volts absolute minimum to turn on for the higher end ones, 10 -15 volts for some of the lower end ones. You didn't mention if you battery pack is 12 or 24 volt but if 24 volt this could be a factor.

If you have a low end controller like a renogy rover, they use a lot of power even when not generating any power - so you can literally have solar power being generated, and the controller consumes much of it.

_________

If you are in an area with a lot of overcast, sometimes it makes sense to use poly panels as they can capture this scattered light better (under some conditions. )
Hi Harry and thank you . Yes my system is with storage at 12 v 3 battery in parallel 12v 110 to c100 . SCC Epever 4210AN and 180w 12v x 4 panels .
 
Three things to consider along with everything else:

1. Your eyes are logarithmic, and what may seem like a bright overcast day to you may actually be quite dark, and what may seem like dark scattered clouds may be quite bright. You'd need a light meter to know for sure - but you already have one - your solar panels, with an appropriate MPPT converter, will match the light level, along with the angle the sun is landing on them.

2. Solar panels are most sensitive to infrared light. While they'll convert all along the visible spectrum, infrared levels will affect them more than visible light levels. Clouds of different types and densities will have an infrared transparency that doesn't match their visible transparency, so some clouds may allow a lot of visible light through and little infrared, or vice versa. One of the biggest factors is whether the cloud has ice in it or not. https://opg.optica.org/josa/abstract.cfm?uri=josa-50-9-876 . Again, what your eyes perceive and what the panels receive may be different.

3. Dirty panels affect the power greatly. If, for instance, you have a month of bright sunny days which result in dust covered panels, then a cloudy day with rain that washes the panels, then a cloudy day that seems darker than the previous day you may find that the seemingly lighter cloudy day produced less energy than the one that seems darker.

These are just a few variables that you would have to track to really understand what's going on - there are many more. It's not a simple problem, and generally it's not worth spending a lot of time on unless you believe there's a significant energy loss and you need to find the cause.
Hi, just to confirm what you wrote, today the day was similar to yesterday's but the results were completely different. Panel power points up to 580 watts to batteries . Thank you for your information.
 
My situation is a good example of your question:

My 200W South-East oriented array starts receiving sun around midday. In sunny days this means I do not produce a single watt until 1PM.
This is partly due to my inverter that requires 10W to inject power to the grid.

In cloudy days I however produce all throughout the day thanks to the irradiation diffraction caused by the clouds; this means I already start producing 15W from 9AM and reach peaks of 40W. The thin clouds disperse light in all directions which allow panels in the shadow to capture more light.

When the clouds are thicker (like during storm) then I will not capture anything.
Similar deal here. One of my arrays is a on west patio that is fully shaded until noon. It's 5.35 kW that on cloudy days it produces 1000 watts or more until noon but on sunny days it struggles to get past 500 until it's fully in the sun.
 
Epever state 2v higher in the manual for the Tracer AN series.

Thanks - will look up some more info on those.

When I looked at that brand in the past I had rejected it for my mobile use applications. I think it was a combination of the size, amazon reviews and country of origin issues at the time but will look again.

Probably I also just didn't believe them that it would really operate with just a 2 volt differential since I tested a few other brands and none of them would "start up" until they hit at least that 5 volt differential point.

Can you tell from this that I got burned on some projects and had to switch out MPPTs for PWM on a few applications?
 
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