Splitting Solar Panels

[s/v Jedi]

Originally Posted by Paul L

Does the MPPT magic voltage tuning actually function in this shadow case with a series panel, i.e. will MPPT controller producer higher output than a standard controller?

Paul, you're in a loop break out of it! May be it's another dimension that you jumped to but you're repeating posts here is all I know for sure

[Paul L]

Originally Posted by s/v Jedi

Paul, you're in a loop break out of it! May be it's another dimension that you jumped to but you're repeating posts here is all I know for sure

Its assisted by the BahamasTel 3G link. You can get in a nasty spiral!!!

[4fish]

Originally Posted by s/v Jedi

1. Same (but can be different) high voltage panels (like 24V nominal for a 12V boat), each with it's own MPPT controller.

My conclusion after this very helpful discussion the best choice for my case will be to get those 2 x 125 of 24 v with independent MPPT controllers.

But Because of space problems I need to get one panel and check the fit (widht) of the second one, since it will be very tight.

I have this options, always only two panels with its own MPPT controllers.

1. 2 x 128 watts panel , 22v. 5,7A.

2. 1x 142 watts panel, 25v. 5.7 A. and 1 x 128 watts panel , 22v. 5,7A.

3. 1x 142 watts panel, 25v. 5.7 A and 1 x 100 watt, 18v panel, 5,7 A

4. 1x 142 watts panel, 25v. 5.7 A and 1 x 51 watt, 9v panel, 5,7 A

OPTIONS:
Is this the correct order of choice as "health" on the system ? and then just choose by power obtained , or is always better to go for the closest voltages even they have independent MPPT controllers?

(all panels are from the same company and same type of cell, I think... )

[noelex 77]

Option 2 with 2 MPPT controllers will give the most AHrs

[4fish]

Ok, that is clear, and will be as "healthy" for the system as option 1, and in the case that is not possible option 3 or even 4 will be also ok ?

[noelex 77]

Originally Posted by 4fish

Ok, that is clear, and will be as "healthy" for the system as option 1, and in the case that is not possible option 3 will be also ok ?

Healthier. More AHrs will keep the batteries in a higher state of charge which Is better for lead acid batteries.

With two controllers all options are OK.

If you want to go for one controller (which is usually cheaper) then matching some of the characteristics of the panels becomes imprortant.

[4fish]

Ok Thank you all,

I think I´ll have things more clear for now !

I´ll try option 2 first ! If it fits....always two controllers....I will give you my final set up ....if I don´t need more help before that, ....

Thanks

[Nicholson58]

HandyBob's Blog « Making off grid RV electrical systems work

Please read Handy Bob Solar. It will take a long while but you will learn a lot about living off-grid on solar panels. You can mix panels if they have simialar specificatons but its better to have all panels identical. Good modern large panels might have about 3 zones in parallel with diode separation. If the panels are diaode protected (usually built-in) you can link your three panels in parallel. This way, if any part of the aray is partly shaded, it can drop out. In series, one shaded zone will pull the whole system down. Series can be done in reliably unshaded places such as an well planned solar farm. Bob's blog has a lot to say about wire size & components components as well as connection plans. He also addresses battery charging, chargers and inverters. He has little nice to say about the average guys selling systems. Keep in mind that Bob has considerably more real estate so he suggests more area and thrifty cells. On a boat, you will pay more for higher watt density. Following the same logic, Bob hasn't much use for MPPT. He just installs more solar instead. BTW, to take max advantage of MPPT, your cells will need to have an open circuit voltage quite a bit higher than the batteries want. I studied this stuff for a long time before we bought stuff. I bought 3 SANYO HT 220watt panels with about 20% conversion efficiency and 54 volts open circuit for our 24 VDC system so also an MPPT. We install this year so I have nothing to relate regarding the results.

[s/v Jedi]

Originally Posted by 4fish

My conclusion after this very helpful discussion the best choice for my case will be to get those 2 x 125 of 24 v with independent MPPT controllers.

But Because of space problems I need to get one panel and check the fit (widht) of the second one, since it will be very tight.

I have this options, always only two panels with its own MPPT controllers.

1. 2 x 128 watts panel , 22v. 5,7A.

2. 1x 142 watts panel, 25v. 5.7 A. and 1 x 128 watts panel , 22v. 5,7A.

3. 1x 142 watts panel, 25v. 5.7 A and 1 x 100 watt, 18v panel, 5,7 A

4. 1x 142 watts panel, 25v. 5.7 A and 1 x 51 watt, 9v panel, 5,7 A

OPTIONS:
Is this the correct order of choice as "health" on the system ? and then just choose by power obtained , or is always better to go for the closest voltages even they have independent MPPT controllers?

(all panels are from the same company and same type of cell, I think... )

The voltages you list are the open, i.e. not connected voltages. You need to check the nominal voltages, for example, my 12V nominal panels have a 22V open voltage. When you use one controller for each panel, then get 24V panels which may give up to 45V output and put that into a couple of BlueSky MPPT controllers. Option 2 yes.

[4fish]

Ok I will take your advice and try to read.....but I always like to listen to people that knows what they are doing, since I may misunderstand something.....

[seandepagnier]

splitting is better as it gives better shade tolerance, if you break one it is less loss, can wire to more configurations (if you change system voltage) and can also be arranged in more positions.

[Paul L]

Originally Posted by Nicholson58

..... Good modern large panels might have about 3 zones in parallel with diode separation. If the panels are diaode protected (usually built-in) you can link your three panels in parallel. This way, if any part of the aray is partly shaded, it can drop out. In series, one shaded zone will pull the whole system down....

That's a direct contradiction to the Jedi's statement above that the shaded panel goes high impedance and the diodes essentially drop it off the series, leaving the other two panels producing normally.

[s/v Jedi]

Originally Posted by Paul L

That's a direct contradiction to the Jedi's statement above that the shaded panel goes high impedance and the diodes essentially drop it off the series, leaving the other two panels producing normally.

Yes, Nicholson explains blocking diodes in parallel operation, which modern panels don't even have anymore for the last 10 years or so (I only learned this recently too and checked that my 10 year old panels have no blocking diodes either, which is true). His info about series operation is even older, from before they invented bypass diodes 20 years ago or more.

All serious arrays are series connected.

[noelex 77]

If one panel is completely, deeply shaded, with zero output, parallel connection is better than series connection.

The real question is what happens when one, or more panels is partially shaded. How do we extract the most power out of these shaded panels that will be producing less voltage and/or current than the panels in full sun.

It is not clear in these circumstances if series or parallel connection is superior although I know there are strong supporters on both sides.

[s/v Jedi]

Originally Posted by noelex 77

If one panel is completely, deeply shaded, with zero output, parallel connection is better than series connection.

The real question is what happens when one, or more panels is partially shaded. How do we extract the most power out of these shaded panels that will be producing less voltage and/or current than the panels in full sun.

It is not clear in these circumstances if series or parallel connection is superior although I know there are strong supporters on both sides.

It is very clear. With partial shading the parallel setup always looses the whole panel, while series setup has a very good chance to still deliver part of it's power.