Series Or Parallel solar panel?

[Bruce K]

Originally Posted by noelex 77

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

Many thanks Nolex 77.

[GrahamHO]

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

All my panels (8 for various other applications including the boat) have BLOCKING diodes already fitted inside the little black box under the the panel where the supplied output cable tail is attached. You can unscrew the cover and see it there already soldered to one of the output terminals. It's purpose is to prevent battery discharge at night. Yes it does result in a SMALL voltage drop but this doesn't matter as the voltage there is high and will be dropped anyway at the controller. I always unsolder the supplied output cable and resolder a new long length of heavier TINNED marine cable being careful to observe the same red and black connections. There is usually an O ring type seal on the box lid. Then start the installation from the panel end threading this long cable down to the controller. The controller should be as close as practical to the battery to avoid cable voltage drop in the now regulated current to the battery. Connect directly from the controller to the + and - of the battery with a protection spade fuse close to the + of the battery. This fuse is essential to guard against a possible battery short circuit for example if a wire ever came loose from the controller.

[noelex 77]

Originally Posted by GrahamHO

All my panels (8 for various other applications including the boat) have BLOCKING diodes already fitted inside the little black box under the the panel where the supplied output cable tail is attached.

It is quite rare for modern solar panels to be fitted with a blocking diode. It is easy to confuse bypass diodes, which are fitted to almost all panels, for a blocking diode, but bypass and blocking diodes have quite a different function. One clue is that there is no point fitting more than one blocking diode per panel. Usually a panel is fitted with between two and eight bypass diodes.

A blocking diode can be fitted, but normally the loss associated with diode is greater than the gain. In addition most solar controllers have a sleep mode that cuts the small discharge through the solar panels at night minimising the blocking diodes function.

Think carefully before you fit a blocking diode. In rare circumstances they are sensible, but in most cases the losses outweigh the gain.

[GrahamHO]

Originally Posted by noelex 77

It is quite rare for modern solar panels to be fitted with a blocking diode. It is easy to confuse bypass diodes, which are fitted to almost all panels, for a blocking diode, but bypass and blocking diodes have quite a different function. One clue is that there is no point fitting more than one blocking diode per panel. Usually a panel is fitted with between two and eight bypass diodes.

A blocking diode can be fitted, but normally the loss associated with diode is greater than the gain. In addition most solar controllers have a sleep mode that cuts the small discharge through the solar panels at night minimising the blocking diodes function.

Think carefully before you fit a blocking diode. In rare circumstances they are sensible, but in most cases the losses outweigh the gain.

Thanks for that information Nolex 77. I get what a bypass diode is used for in series applications i.e. as I understand to bypass a non performing cell or panel in a series configuration. So what is the purpose of the diode always, in my experience, pre-installed inside the black box under the panel; where the output cable is attached? I have just this minute opened the box under a new panel to double check. There is a diode in line with the + output. I put a multimeter on it to check and it only allows continuity out of the panel but not into the panel. To my way of thinking this is a blocking diode. Perhaps it is not normal in modern panels to fit an ADITIONAL blocking diode as one is already fitted at the factory? Fitting another would certainly result in an unnecessary voltage drop. That's as I see it anyway. I would welcome being corrected about this if I'm not right.

[noelex 77]

The solar cells (typically 36) in a panel are connected in series without bypass diodes fitted within the panels these cells can suffer local overheating in shaded conditions. So most solar panels have bypass diodes installed to protect the cells.

Generally a minimum of two are required, but some panels fit more. These cannot be added externally.

Blocking diodes are different, they reduce the measured panel output, they can easily be added externally, and usually are not needed.

If they were fitted internally a 100w panel would become a 97w panel ( And would need to labeled thus) so manufacturers would be silly to fit one.

[GrahamHO]

Originally Posted by noelex 77

The solar cells (typically 36) in a panel are connected in series without bypass diodes fitted within the panels these cells can suffer local overheating in shaded conditions. So most solar panels have bypass diodes installed to protect the cells.

Generally a minimum of two are required, but some panels fit more. These cannot be added externally.

Blocking diodes are different, they reduce the measured panel output, they can easily be added externally, and usually are not needed.

If they were fitted internally a 100w panel would become a 97w panel ( And would need to labeled thus) so manufacturers would be silly to fit one.

Thanks Nolex 77. Perhaps a 103 W panel becomes a 100 W? Your 200 horsepower car is probably only 80 horsepower at the wheels. Anyway the panel wattage rating is simply a generic one as the wattage varies with the sunlight.

I'm not sure how to post a photograph in the forum. If you don't mind explaining that to me I will post a photo of a diode fitted inside the black box built in under a solar panel manufactured by a "silly manufacturer".. It IS a diode. It IS in line with the positive output. It ONLY allows current flow "out" not "in". I have checked that with a meter. They are installed in every panel I have worked with.

For those that don't understand diodes. Simplified they are like a one way valve in a water pipe that allows water to leave a supply but prevents a back flow of contaminated water siphoning back into the supply in the event of a loss of pressure.

[newhaul]

I posted this link in post 22 of this thread it shows a bypass diode and a blocking diode in the factory junction box of a panel http://vandogtraveller.com/wp-conten...ar-diodes1.jpg

[noelex 77]

Originally Posted by GrahamHO

Thanks Nolex 77. Perhaps a 103 W panel becomes a 100 W? Your 200 horsepower car is probably only 80 horsepower at the wheels. Anyway the panel wattage rating is simply a generic one as the wattage varies with the sunlight.

True, but for two identical panels, one without a blocking diode would be rated, labeled and sold as 100w and the one with a blocking diode as a 97w panel. Most consumers, including me, would buy the 100w panel.

Originally Posted by GrahamHO

I'm not sure how to post a photograph in the forum. If you don't mind explaining that to me

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Originally Posted by GrahamHO

It IS a diode. It IS in line with the positive output. It ONLY allows current flow "out" not "in". I have checked that with a meter. They are installed in every panel I have worked with.

Bypass diodes are physically the same devices as blocking diodes, just wired in a different way. As they are diodes, they only allow the passage of current one way. One of the bypass diodes will be connected to the positive output. Don't assume because the diode is connected to the positive output lead that it is a blocking diode it could be a bypass or a blocking diode depending on the connection point of the anode side of the diode.

Originally Posted by newhaul

I posted this link in post 22 of this thread it shows a bypass diode and a blocking diode in the factory junction box of a panel http://vandogtraveller.com/wp-conten...ar-diodes1.jpg

I think we are going around in circles. I believe the photograph shows two bypass diodes for the reasons I gave in post 25.

[noelex 77]

With a quick google search I have not found a single manufacturer that lists a blocking diode in their specifications. That is not to say they are never installed by the manufacturer, (they are sensible on some very small battery maintainer panels designed for use without a controller) but they must be rare. All panels have bypass diodes and many people mistake these for blocking diode(s).The function of blocking and bypass diodes are different, although the diodes themselves are identical.

This is from the installation manual for the popular Kyocera panels:

http://www.kyocerasolar.com/assets/001/5155.pdf

"KYOCERA modules do not contain a blocking diode when shipped from the factory"
"Factory Installed Bypass Diode (Qty)....yes (4)"

A Blocking diode can always be added later if it is sensible (it rarely is). Bypass diodes between the cells cannot. Bypass diodes between the cells require access to internal connections between the solar cells so cannot be retrofitted. This is why the manufacturer makes the solar panel with the bypass diodes already installed in the junction box.

[colemj]

Solar panels have such a high reverse resistance, that a blocking diode really isn't needed. I haven't met a controller yet that does not provide a blocking function (although they probably do exist).

That photo shows two bypass diodes - one for each side of the panel. The tell is that they are both connected to the center connector, which is the panel split point. A blocking diode would be across the whole panel output.

Mark

[GrahamHO]

Originally Posted by colemj

Solar panels have such a high reverse resistance, that a blocking diode really isn't needed. I haven't met a controller yet that does not provide a blocking function (although they probably do exist).

That photo shows two bypass diodes - one for each side of the panel. The tell is that they are both connected to the center connector, which is the panel split point. A blocking diode would be across the whole panel output.

Mark

Interesting that the controllers provide a blocking function, which makes sense.
I have mainly Solarland panels and they each have a diode interrupting the + output. That is, in series with the + and not across. Solarland has a lot of information on their web site though I can't see reference to diodes. I can't see much of a disadvantage excepting in marginal sunlight conditions as usually the panel is delivering more voltage than needed. This diode connection would prevent possible damage ( as I see it ) if there were several panels in parallel before the controller and one was in shade and others in bright sun. I tried to upload a photo but apparently my iPad camera had the wrong file type as the upload attempt told me. I'll try later with a proper camera, though you get the idea of it being in series. Easy enough to bridge but I think unnecessary. My whole system works fine including a couple of weeks away a few years ago when my alternator wasn't working and the motor would always start and lights would always work. I just didn't try to use the anchor winch or the electric fridge.

[noelex 77]

Originally Posted by GrahamHO

Solarland has a lot of information on their web site though I can't see reference to diodes.

Solarland have reasonable documentation of their panels.

Their installation instructions list the type of bypass diodes fitted. There is no reference to blocking diodes I strongly suspect this is because there is no blocking diode is fitted.

Originally Posted by GrahamHO

I can't see much of a disadvantage excepting in marginal sunlight conditions as usually the panel is delivering more voltage than needed.

If you do fit a blocking diode a simple way to look at the loss is that as each solar cell produces about 0.5v and the diode loss is close to 0.5v for a nominal 12v panel the bypass diode will mean a 36 cell panel will perform in daylight hours as if it is a 35 cell panel.

Another way to look at the loss during daylight is that the Vmp will be reduced by 0.5v. As a typical Vmp is about 18v under STC the loss is 0.5/18 =2.8%. With an MPPT controller this will be very close to actual loss. To calculate the loss with a non MPPT controller is complicated. The loss will be close to zero until the Vmp drops below the battery voltage, then the loss is close to 100%. On average the loss is close to same as seen with a MPPT controller (2.8%).

Most controllers will disconnect the solar panel at night so this loss (2.8%) is close to what is seen in practice. If you have a direct connection to the batteries and do not have a solar regulator (or one of the very rare models that does not disconnect the panels under low light conditions) the night time discharge will offset this 2.8% loss. With most panels the night time discharge is very slight so there will still be a significant net loss, but if you do not have a controller, a blocking diode does provide some protection for long periods of zero solar panel output such as if the panels covered in snow.

Originally Posted by GrahamHO

This diode connection would prevent possible damage ( as I see it ) if there were several panels in parallel before the controller and one was in shade and others in bright sun.

There is no risk of damage in these circumstances without a blocking diode.

[weijing3333]

Knowledge to learn:
Solar Panels - Series or Parallel ?
Four Solar Panels - Parallel , Series or Series-Parallel

Products to choose:
Solar Panels