Paralell strings of solar panels

[AlexanderKristiansen]

Hi! Sorry if this has been answered before.

I have 4x255 2S2P solar panels and I am thinking about expanding with another string of solar panels in parallel with the others. The other identical string will have another location and will have shade when the other string is producing at maximum (and the other way around). Will the string in shade affect the string in sunlight?

Both strings will operate at about 78V and 16Ah.

 

[time2roll]

No, the shaded string in parallel will not affect the power produced by the panels in the sun.

 

[AlexanderKristiansen]

No, the shaded string in parallel will not affect the power produced by the panels in the sun.

Great, thanx a lot

 

[meetyg]

No, the shaded string in parallel will not affect the power produced by the panels in the sun.

Are you sure about that?
I thought that that's the reason why blocking diodes are recommended for each parallel string: in order to avoid flow of current from one string to another.

 

[houseofancients]

Are you sure about that?
I thought that that's the reason why blocking diodes are recommended for each parallel string: in order to avoid flow of current from one string to another.

that is, as far as i know a theoretical thing.
the theorie is that if 1 string is in the shade, it will not produce any voltage, therefor cause a flowback from the string that does produce voltage.
unless a string is fully covered it will always produce voltage, therefor in the real world it should cause an issue..

i havent tested this personally, but andy ( offgrid garage ) does have a video about it

 

[AlexanderKristiansen]

that is, as far as i know a theoretical thing.
the theorie is that if 1 string is in the shade, it will not produce any voltage, therefor cause a flowback from the string that does produce voltage.
unless a string is fully covered it will always produce voltage, therefor in the real world it should cause an issue..

i havent tested this personally, but andy ( offgrid garage ) does have a video about it

Sometimes both strings will produce power, other times only one of them (partial shaded and completely)

Could you possibly post a link to the video?

 

[houseofancients]

Sometimes both strings will produce power, other times only one of them (partial shaded and completely)

Could you possibly post a link to the video?

 

[meetyg]

Well, as he mentions, it's not a very accurate test using his equipment and setup.
In theory, if one of the strings was very shaded, it would draw the current of the others.

 

[AlexanderKristiansen]

Well, as he mentions, it's not a very accurate test using his equipment and setup.
In theory, if one of the strings was very shaded, it would draw the current of the others.

To prevent drawing current from the others strings, would I need a blocking diode on each string?

 

[meetyg]

Yes, that's the recommendation.
Will explains it well, although addressing a combiner box, but the principle is the same:

I am using blocking diodes that are integrated into MC4 connectors, which makes it easier to connect. Just make sure you get ones rated appropriately for your voltage and max current of each string.

 

[houseofancients]

again, theory sounds great, real world application a lot less.
just add more complexity for a very minimal gain, so not worth it ..

of course imho so the OP should do what ever he seems fit

 

[AlexanderKristiansen]

again, theory sounds great, real world application a lot less.
just add more complexity for a very minimal gain, so not worth it ..

of course imho so the OP should do what ever he seems fit

Thanks for the advice, how would you define a minimal gain?

 

[houseofancients]

Thanks for the advice, how would you define a minimal gain?

in my case it was about 5%

 

[AlexanderKristiansen]

in my case it was about 5%

That's not much Is this the best-case or worst-case scenario?

 

[houseofancients]

That's not much Is this the best-case or worst-case scenario?

this was worst case, but again in my situation.
partial shading of 1 panel in a 2p series of 8 panels

 

[meetyg]

I'm not worried about losses, which may or may not be significant. I'm trying to protect my panels from unnecessary heat, which current flow can cause.
If you are talking about temporary shading, for short periods of time, then maybe it's negligible. But if you have a setup where some panels are shaded constantly for certain times of the day, not only are you wasting energy, but you could also damage the other panels causing them to heat up unnecessarily.
We all know that panels perform better when cooler, so although they are shaded, they will actually get hotter and perform worse when the do get sun.

 

[time2roll]

Are you sure about that?
I thought that that's the reason why blocking diodes are recommended for each parallel string: in order to avoid flow of current from one string to another.

Have you measured the loss of power back feeding through a parallel set of panels at similar voltage and shaded conditions?

 

[coolbz]

When panels are connected to large load, the voltage drops alot. In my setup, I have 7s 255VOC, it becomes 210V when all in one inverter is turned on, if I run a 1000watt load, my solar string drops to 155V. So imagine you have several strings, they will level out to same voltage with each string providing some amount of watts. If there is no large enough load, the low voltage panel string will simply cut off by it's diode for protection.