Blocking diodes for paralleled panels?

[CatNewBee]

Originally Posted by Axel_G

No, you do no need diodes for parallel panels.



The voltage of the shaded panel will only marginally go down, unless it is completely dark (cover it with a tarp or so). Its ability to drive current will be reduced, but that is not an issue here. So as it maintains the same voltage there will be no current flowing backward.



So basically you have a working panel, that will have an idle voltage at maybe 18V which is loaded to 16V and 6A by the MPPT tracker as this is approx. the point of the maximum power.

And you have a shaded panel which will still give 17V but maybe only 0.1A. But the voltage is still above the loaded voltage of the good panel. It will still give some 0.1A into the battery, which is the issue with shading.



Diodes will consume a lot of energy though. And the MPPT tracker already has one for the night to make sure there is no current flowing into the cells.

As I said, 2 parallel, no problem. more parallel increasing problem.
You mayhave heard about bypass diodes, they work because shaded cells do not provide amps and there is a voltage break through when they are inverted in polarity by the voltage / circuit of the remaining unshaded cells. The bypass diodes protect the shaded cells from run-off and get damaged producing hot spots on the panel. There are pictures on the Internet of such incidents. Especially with flexible panels glued to Fiberglass or put on canvas, those hotspots can start a fire. A single 100Wp panel does usually not provide enough energy to do so, but if you have 10 of those and one is defective, the other 9 may provide enough to produce some smoke.

Read the panel tech data. Good manufacturer print on the label the fuse for the string to be used, that will blow in such a situation. Alternative you can use string diodes. Take Schottky Diodes, they have 0.2..0.3V voltage drop in contrast to 0.7 for silicium rectifier diodes. you loose on a 100Wp panel 17.5V Vmp at 5.7A nominal 1.2W or 1.2% at Wmp, usually less, because of flat mounting, so not a big deal at all.

[skipgundlach]

Some folks think it's a good idea for blocking diodes on Parallel installations:

If you're doing parallel, you want to have bypass diodes inline on the
+ legs to accommodate the differences in shading.

Reference:

https://www.electronics-tutorials.ws...ss-diodes.html

Connecting Solar Panels Together For Increased Power

https://www.altestore.com/blog/2016/...-solar-panels/

https://www.solar-electric.com/learn...rs-cables.html

I got mine at under $10 a pair on ebay, I think it was...

Oops. Half that:

https://www.ebay.com/itm/20A-MC4-PV-...-/232606298048...

[CatNewBee]

there are 15A Schottky diodes for 10ct a piece.
https://www.google.fr/shopping/produ...RqyDLgQgjYIqgI

[ramblinrod]

Originally Posted by skipgundlach

Some folks think it's a good idea for blocking diodes on Parallel installations:

If you're doing parallel, you want to have bypass diodes inline on the
+ legs to accommodate the differences in shading.

Incorrect.

If you are connecting panels in series, and the panels do not have internal bypass diodes, then you may consider using bypass diodes to pass current through the diode in parallel with the shaded panel

Else the shaded panel will block current flow through all panels connected in series.

Connected in parallel, if a panel is shaded, it will not pass current but all other unshaded panels connected in parallel do pass current.

When connecting panels in a series parallel array, one has to ensure the voltage cannot exceed the max voltage rating of the bypass diodes (internal or external) of the parallel connected series array.

[hzcruiser]

Originally Posted by Axel_G

No, you do no need diodes for parallel panels.

The voltage of the shaded panel will only marginally go down, unless it is completely dark (cover it with a tarp or so). Its ability to drive current will be reduced, but that is not an issue here. So as it maintains the same voltage there will be no current flowing backward.

[...]

That's a valid point, Axel. The panel that's facing the other direction is not completely in the dark. Its voltage might be significantly lower though, as in say 5V less, which then would lead to losses that are higher than the losses from the blocking diodes.

I guess it comes down to testing that with a clamp meter on your actual panels.

[john61ct]

Ideal in that case is 1:1 controller per panel

[Axel_G]

Originally Posted by hzcruiser

That's a valid point, Axel. The panel that's facing the other direction is not completely in the dark. Its voltage might be significantly lower though, as in say 5V less, which then would lead to losses that are higher than the losses from the blocking diodes.

I guess it comes down to testing that with a clamp meter on your actual panels.

For the voltage to go down to 5V it must be dark. Even shade will still produce 15-16V, albeit at almost 0 current. A solar cell is a current source with almost flat voltage output, it will deliver 14V as soon as there is some light. (This is the reason it does not make sense to connect solar panels serially to boost the voltage to get power from the early morning sun)



After all a Solar Cell is a diode in itself, when current is trying to flow reversely it will block it. And in a parallel connection the voltage is not high enough to damage the panel.




There is simply no need for a blocking diode, but it is an additional part than can fail, that gets hot (a Schottky Diode at 1.2W will get very hot), that requires additional connections and that looses power.



That is of course completely different to a seriall connection, there the voltage can get dangerously high and there the bypass diode is absolutely necessary.

[hzcruiser]

Originally Posted by Axel_G

For the voltage to go down to 5V it must be dark.

Agreed. And if you read my post again, I wrote 5V less, not 5V. (There is a potential difference here, LOL.)

[ramblinrod]

Originally Posted by john61ct

Ideal in that case is 1:1 controller per panel

For 1-3 panels, then I gets a little ridiculous and creates too many potential failure nodes.

For 8 x 100 W panels, symmetrically placed in a 2x4 array, then 2 controllers makes sense. For 3x3 array, 3 controllers makes sense.

I would never recommend 8 charge controllers for an 8 times 100 W panel system.

[seandepagnier]

you need bypass diodes not blocking diodes for partial shade

[rgleason]

https://www.electronics-tutorials.ws...ss-diodes.html

[Paul Elliott]

In my experience, you don't need blocking diodes when connecting identical panels in parallel. As an experiment, I took two Renogy 100W panels and wired them in parallel, with a voltmeter measuring panel voltage and an ammeter measuring panel current to a variable load (some lightbulbs and a giant power rheostat I have). I connected a second ammeter to measure any current from one panel to the other.

With both panels in full sun, the panels delivered very close to rated open-circuit voltage (Voc) and short-circuit current (Isc). They delivered typical volts/amps to my test load.

With one panel completely shaded, no load, there was a trivial amount of back-current into the shaded panel -- only a few milliamps. When I put any significant load on the panels the back-current was zero.

I then disconnected everything and hooked up a variable power supply to one completely shaded panel. There was no significant back-current until I exceeded Voc. I might be able to dig up my measurement data if anyone cares.

So with these two panels anyway, there is no need for blocking diodes.

[missourisailor]

A year or so ago, I did the exact same test that Paul did, with the exact same results.

Two Sun Power 100 watt flexible panels.
500watt, wire round potentiometer for a load.
Several VOM’s and two, cheap Ah counters.
NO added diodes!

The outputs were pretty much close to equal, whether the panels were paralleled with one fully shaded. Or with just a single panel connected to the load.

What I want to know is if anyone else has done an output test using 1:1 controller/panel configuration.

I did a quick and dirty test following the above test using some old BlueSky MPPT controllers that came off a clients system.
The results were not what I expected. In a 1:1 set up, the output was less (about 2~3%) than with paralleled panels driving one controller.

Not anywhere close to what I’ve been told by the manufactures and so called “internet experts”.

Just wondering if I fubarred the test some how.

[ramblinrod]

Originally Posted by missourisailor

A year or so ago, I did the exact same test that Paul did, with the exact same results.

Two Sun Power 100 watt flexible panels.
500watt, wire round potentiometer for a load.
Several VOM’s and two, cheap Ah counters.
NO added diodes!

The outputs were pretty much close to equal, whether the panels were paralleled with one fully shaded. Or with just a single panel connected to the load.

What I want to know is if anyone else has done an output test using 1:1 controller/panel configuration.

I did a quick and dirty test following the above test using some old BlueSky MPPT controllers that came off a clients system.
The results were not what I expected. In a 1:1 set up, the output was less (about 2~3%) than with paralleled panels driving one controller.

Not anywhere close to what I’ve been told by the manufactures and so called “internet experts”.

Just wondering if I fubarred the test some how.

Well, the controllers consume power; so if one connects more controllers than needed, the power consumed is lost
Panel output.

[rgleason]

Briefly, because I don't want to hyjack the thread, what have I done wrong or missed for the PV wiring in this diagram ,

- Dodger (2) Port & Starboard, PV approx 80 watts
- Stern where Bimini would be (2) PV 130 watts

1. Do I need disconnects? Location? Would fuse removal be ok?
2. Any changes needed to the wiring diagram?

3. What is the best way to wire it? I am showing 3 controllers right now?
You could leave any comments on the other thread so it doesn't interrupt this thread. Thank you.