Series Or Parallel solar panel?

[jeepbluetj]

Not only what noelex said, but the OPs panels are 24v panels. They won't fall below 12v. I have a very similiar system on my motorhome. 2 240w panels in parallel. Series would have been very close to the max input voltage of my controller, so they're in parallel.

Series helps reduce v-drop from the panels to the controller. But there has to be some bypass diodes to handle shading. Parallel is simple and works. At 24-30v, wire size is halved from 12v for current capacity from panels to controller.

[newhaul]

Originally Posted by catman

To KISS or not.
Unfortunately if you connect a shaded solar panel to a non shaded solar panel in parallel the parallel connected panels will give an averaged output which will be less than 12 volt. If each panel has its own controller the controller output will never be lower than the load (internal diodes) which means only the solar panel,that is in the sun will charge your batteries.
Cheers, Catman

Umm no a shaded panel will not affect the output of any other panel in the parallel setup due to what has become an industry standard called a blocking diode that allows power from an item but not power to the ipanel from any other source

[noelex 77]

Originally Posted by catman

To KISS or not.
Unfortunately if you connect a shaded solar panel to a non shaded solar panel in parallel the parallel connected panels will give an averaged output which will be less than 12 volt. If each panel has its own controller the controller output will never be lower than the load (internal diodes) which means only the solar panel,that is in the sun will charge your batteries.
Cheers, Catman

If you have one solar panel in the sun and connect another solar panel in parallel that is covered (so that it is receiving no light) the total output current and voltage will not change (a very slight discharge and loss of power will occur through the shaded panel in theory without a blocking diode, but in practice this will be very slight).

[sparrowhawk1]

This old house the pbs tv show just showed professional solar panel installation on a house. They said most houses are wired in series but this causes all panels in a" group" to lose power when one is shaded. They were installing panels on a roof that gets partially shaded, that's why the company wired their panels parallel so that only the shaded panels will be lost. I just watched it the other day so you might be able to watch it again.

[noelex 77]

Originally Posted by newhaul

Umm no a shaded panel will not affect the output of any other panel in the parallel setup due to what has become an industry standard called a blocking diode that allows power from an item but not power to the ipanel from any other source

Blocking diodes are quite rare in solar panels these days. Nearly all panels have bypass diodes but these serve a different function.

A blocking diode would reduce the output wattage specification of the panel and is not normally necessary. Most solar controllers will cut the connection with solar panel under very low light conditions. The very high resistance of a deeply shaded solar panel means the potential discharge is very low in any case.

In rare cases a blocking diode can be beneficial. They are easy and cheap to fit, but usually the insertion loss of the diode is greater than the very slight reduction in discharge.

[newhaul]

http://www.google.com/search?redir_e...use%20episodes just have to find out what episode it was

[newhaul]

Originally Posted by noelex 77

Blocking diodes are quite rare in solar panels these days. Nearly all panels have bypass diodes but these serve a different function.

A blocking diode would reduce the output wattage specification of the panel and is not normally necessary. Most solar controllers will cut the connection with solar panel under very low light conditions. The very high resistance of a deeply shaded solar panel means the potential discharge is very low in any case.

In rare cases a blocking diode can be beneficial. They are easy and cheap to fit, but usually the insertion loss of the diode is greater than the very slight reduction in discharge.

Since you brought up the bypass diodes the diode for the whole panel is mounted in the junction box right beside the blocking diode
http://vandogtraveller.com/wp-conten...ar-diodes1.jpg

[GrahamHO]

Originally Posted by Bruce K

I am about to install 2 new Sharp 188w PV panels. Open circuit voltage 29.6V my 30a MPPT controller max ocV is 65V, so that is Ok. I think I will connect the panels in series to minimise cable loss. Panels are mounted flat on roof so should never be 100% output. Panels may occasionally have a small amount of shadowing. Any thoughts from those who know? Regards BK

With a similar setup I wire my panels in parallel. That is + to + and - to -.
To minimise cable loss have the controller close to the batteries. Then the only cable loss is minimal in the short cable to the battery. The loss in the cable from the panels to the controller doesn't matter much as it is stepped down at the controller. I run separate cables from 2 panels to a junction near the controller. That way the connection is inside the boat and it minimises any voltage loss.

If you connect the panels in series you will have 60 volts which is a bit close for comfort to your rated 65 v. The biggest problem with series connection is that a shadow on one panel it will cut both panels down to the shaded panel voltage. With parallel the panel in the sun still gives full voltage.

[nimblemotors]

I thought I explain it very simply in the electric-boat-forum posts...

If you put panels in parallel, they must have the same voltage, that is an electrical fact. Panels all have blocking diodes, so current can't flow IN to a panel. If one is shaded, the only way it can contribute is by having the same voltage as the non-shaded panels, which makes it drop its current to raise its voltage, and if shaded enough that current will drop to essentially zero.

That sounds bad, but putting them in series can be worse, as shade can make BOTH panels output almost zero.

Also, having high voltage on your boat can be dangerous.
Generally 48 volts dc is consider the limit for safety, which rules out series connections pretty much right there.

[noelex 77]

Originally Posted by newhaul

Since you brought up the bypass diodes the diode for the whole panel is mounted in the junction box right beside the blocking diode

I think the diode on the right has been mislabeled on the photo and is a bypass diode, not a blocking diode. (who made the notes on the photo?) Most 12v panels fit at least 2 bypass diodes mainly to protect the cells from overheating in partial shade. Some panels have many more (the popular Kyocera panels normally have 8 bypass diodes).

If it was a blocking diode, it would need to be fitted in series with one of the output leads.

The panel looks like it has been divided into two strings, which is a common common configuration for a 12v panel . The diode on the left is in parallel with one string and the diode on the right is in parallel with the second string.

It is difficult to sure, there is nothing to stop a manufacturer fitting a blocking diode, but they rarely do so. It would reduce the specified wattage of the panel for a start which would put them at a competitive disadvantage, as well as generally being unnecessary.

[newhaul]

Originally Posted by noelex 77

I think the diode on the right has been mislabeled on the photo and is a bypass diode, not a blocking diode. (who made the notes on the photo?) Most 12v panels fit at least 2 bypass diodes mainly to protect the cells from overheating in partial shade. Some panels have many more (the popular Kyocera panels normally have 8 bypass diodes).

If it was a blocking diode, it would need to be fitted in series with one of the output leads.

The panel looks like it has been divided into two strings, which is a common common configuration for a 12v panel . The diode on the left is in parallel with one string and the diode on the right is in parallel with the second string.

It is difficult to sure, there is nothing to stop a manufacturer fitting a blocking diode, but they rarely do so. It would reduce the specified wattage of the panel for a start which would put them at a competitive disadvantage, as well as generally being unnecessary.

You must be a solar service provider in some way.current or retired they have both diodes

[sparrowhawk1]

Ok did a little research its This Old House season 13 episode 26. But this is for grid a tie system and they use individual inverters on each panel. the reason they do this Is so they don't have to run the panels in series.( and the higher voltage lets them use smaller wires )I'm back to not being sure if this applies to panels connected to a MPPT controller. Just read nimble motors post so I'm keeping mine parallel when I add more

[GrahamHO]

Slightly off topic but still regarding cable loss from solar panels. Panels often come with a cable tail coming out of a small box under the panel. That box contains a diode. I have found that often this cable tail is plain copper wire ie not tinned. Best to open the box and unsolder the tail then solder your long TINNED cable to where the original tail was attached. Of course observing red to + and black to - . This gets rid of one unnecessary connection and substitutes tinned cable for the plain copper which will deteriorate and cause quite a voltage drop.

[Bruce K]

OK If I connect in parallel is there any advantage in fitting a bypass diode to each panel, if so what size and type of diode, and how to connect? Regards BK

[noelex 77]

Originally Posted by Bruce K

OK If I connect in parallel is there any advantage in fitting a bypass diode to each panel, if so what size and type of diode, and how to connect? Regards BK

No advantage. Bypass diodes are only needed in series connections.