solar panel - semi-flexible with bypass diodes

Hi all, I'm in the market for a solar panel though I'm not finding one with both these features. It will be propped up on a lead out from a ute-camper - so I like the light weight of the semi-flexible type. However I seek out shade to set up the camper in the intense heat, so having some shade on the panel may be unavoidable (given the limitations of cable length) - hence the need for as many bypass diodes as possible to keep it working in partial shade. Is such a beast made? Cheers.
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Reply By: olcoolone - Wednesday, Apr 23, 2014 at 09:03

Wednesday, Apr 23, 2014 at 09:03
QUOTE "hence the need for as many bypass diodes as possible to keep it working in partial shade"

This only works if you have multiple panels and one or more panels are going to be shaded for an extended period, on one panel it will make no difference.

More bypass diodes is not the best and can hinder performance.

The other problem with a flexible panel is it is harder to adjust it for maximum sunlight and to follow the sun.

Portable non flexible panels are ideal for this as you can change the angle and direction through out the day.

I would also suggest a good quality inline amp meter between the panel and the battery so you can get maximum sunlight and adjust accordingly.

How long is you cable?
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Reply By: HKB Electronics - Wednesday, Apr 23, 2014 at 15:46

Wednesday, Apr 23, 2014 at 15:46
I have seen panels with three main segments, and three bypass diodes not flexible units though, generally for fixed installation, the problem with using one panel will be if one segment is shaded you'll lose a third of your voltage and probably won't have enough volts to charge then battery anyway unless you can get a 24V panel and a 12V MPPT that can handle the higher voltage.


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Reply By: Member - Boobook - Wednesday, Apr 23, 2014 at 16:27

Wednesday, Apr 23, 2014 at 16:27

To my knowledge all, or certainly most solar panels have bypass diodes built into the terminal block. I have 4 semi flexible panels and all have them.

However you may be referring to blocking diodes, and none have those.

Putting it simply, bypass diodes are useful for partial shading IF YOU HAVE panels in series, (+ to - ) and run a MPPT system with 24, 36v or more which is unlikely for RV applications.

However if you have panels in parallel, with or without a MPPT system, then you will need 1 blocking diode for each panel. This is probably what you are looking to do.

If you only have one panel then you need nothing, unless you have no controller in which case you need a blocking diode.

You will need to source and install the blocking diode if you need them. Get schottkey diodes for their low voltage drop, and only one per panel. + of the panel is wired to the anode of the diode. You can get then on ebay or at Jaycar. Make sure they are rated at a higher current than each panel
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Reply By: Cybermike - Friday, Apr 25, 2014 at 22:56

Friday, Apr 25, 2014 at 22:56
I don't have any cable yet to connect the panels to the controller that will be mounted in the ute, though I like the idea of wiring 2 panels in series to get about 36 volts and an MPPT auto switch controller to provide about 14 volts to the battery. There's many volts available to lose between those 2 figures, so there will be practically no limitation on cable length & I can really chase the sun for the panels while the ute is camped in the shadiest spot available.

Also, there is there any issue with feeding the regulator into a busbar (powering cigarette sockets) in the ute canopy, where there will be approx. 0.2 volt drop to the spiral wound AGM battery under the bonnet?

Regards, Mike.
AnswerID: 531228

Follow Up By: HKB Electronics - Saturday, Apr 26, 2014 at 13:39

Saturday, Apr 26, 2014 at 13:39
Always better if regulator is mounted as close to the battery as possible, in your case as long as the cabling can handle the charge current a .2V drop is workable.


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Follow Up By: Member - John and Val - Saturday, Apr 26, 2014 at 15:29

Saturday, Apr 26, 2014 at 15:29

A few misconceptions here. An MPPT controller takes the available voltage, draws sufficient current to load the panels down to their optimum power voltage, then converts that voltage down to what the battery requires. An MPPT controller doesn't discard the excess voltage - it effectively uses the energy it represents to generate extra amps. "There's many volts available to lose between those 2 figures" - No! In fact voltage losses between the panel and controller not only waste energy, they upset the operation of the controller. Losses are less critical on the panel side of the regulator, but best minimised anyway.

There are a few (very few) MPPT controllers around that will accept higher panel voltages, but most for 12V battery charging are intended to interface with panels that have an unloaded voltage of about 23-24 and a maximum power point at about 17-18 volts.

There are advantages in series connection, but also a there's a downside. The power output of series connected panels is governed by the panel with lowest output. So a bit of shading on one panel affects the power supplied by all panels. With a parallel connection that shading only affects the one panel.


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Reply By: Cybermike - Sunday, Apr 27, 2014 at 22:31

Sunday, Apr 27, 2014 at 22:31
It sounds like there could be times when panels in series have an advantage over parallel, & times when it is vice-versa (e.g. shading). I'm wanting to get 200 watts of panel, & am thinking 4 * 50 watt semi-flexibles attached onto a home-made mobile frame, to give both paralel & series options. The Tracer regulator I'm looking at will go to at least 80 volts.

I realize there will be power losses due to having 4 fittings as opposed to 1 if I had a single panel, though I like the versaility for handling a variety of camping situations. The cable will be sized for the greatest amp option (panels in parrallel).

Regards, Mike.
AnswerID: 531378

Follow Up By: Member - Boobook - Monday, Apr 28, 2014 at 07:14

Monday, Apr 28, 2014 at 07:14
Mike you're right but in practice the difference is minimal so plan for one or the other. Also there is a 100v tracer MPPT available, usually for a few dollars more. They are a brilliant MPPT charger and true MPPT.

An advantage of parallel is that it is easier to move the panels apart from each other if you have separate cables. I have 2 x 15m cables and a y cable which is 2 m long and use red anderson connectors ( which won't fit into grey ones). That way they can be 30m apart or next to each other 30m from the camper. I used good speaker cable which is very flexible and thick.

Also I think it would be cheaper to get 2 x 100w panels or better still 3 x 80W.

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