24vdc Solar to 12vdc Battery Bank

[ChuckSK]

cal40john

Until you understand the purpose and function of bypass diodes, you will continue to be wrong.

Chuck

[cal40john]

Originally Posted by ChuckSK

cal40john

Until you understand the purpose and function of bypass diodes, you will continue to be wrong.

Chuck

I don't believe that we were talking about flexible amorphous silicon panels since many people don't use them since they require so much more space. They have bypass diodes across each cell. The crystalline panels that I have recently seen advertised with bypass diodes happen to just have a bypass diode installed across the output leads to bypass the entire panel as a whole. So yes I can see that this would limit you to a maximum of 50% power loss. Does the second panel in light forcing more current through the shaded panel cause it to bypass fairly early dropping you to 50% output (actually less since you subtract the small 0.7 volt drop from the bypass diode), whereas parallel operation would allow whatever output the shaded panel could put out being added to the unshaded output?

I wrote in my previous post my understanding of how it works. If someone knows more than I, and teaches me more, great. I asked to poster of the information to clarify and teach me where I was wrong.

If you just want to be rude, go back to Sailing Anarchy.

John

[Pelagic]

I really appreciate the fact that this discussion can help those of us with no experience to reduce the technical confusion or “marketing” claims of the various solar components down to an informed user’s level before making a substantial quality purchase.

I am still confused about how critical this shading issue is, because on a two mast boat we have limited real estate that will not get shade from Mast or Stays as the Sun angles change

For example:

If shading could be properly managed by panel selection that use better diodes and parallel wiring should I consider mounting more panels on the large stainless Bimini I made last year for the whole cockpit?

This is a useable additional area of about 2.5m x 3.0m that I show in 2 Blue sections.

At anchor the boom would be resting in a crutch in between, but I would still have the stays and mast and probably topping lift giving occasional shade as we swung at anchor.

Underway, I would expect at least 50% to be shaded by the sail since the aft sail is more a reaching sail

So would you consider that area as a viable consideration or because of shading... just stick with making a new rack above the tender?

Thanks again for your advice and even disagreements.

I am still trying to come to grips with what actually works in real life

[hellosailor]

"and trigger the module to protect itself "
I have to wonder if that got mangled in the translation, because AFAIK the module lacks the intelligence (biological or electronic) to actively "protect" itself from anything. Unless they forgot to mention there are active electronics or switching transistors built in somewhere?

Pelagic, it would appear from Kyocera's "hints" that you have a choice of two evils. Wire the panels in parallel, and you may lose 2-4% all the time because you are providing a lower maximum feed voltage to the MPPT controller. Or, wire them in parallel, and you will lose 50% anytime either of them is even partially shaded. (Until Darwin breeds a more intelligent module, yeah.)

Just seems like "parallel" is the clear winner unless your panels will be shade-free 99(?)% of the time. Those 50% output hits have got to outweigh a lot of 2-4% losses, something like 1 hour of any shade would equal 12-25 hours of lower (parallel) output loss, as I see it.

[ChuckSK]

"trigger the module to protect itself"
means that the resistance of the shaded cells has increased to the point that the voltage drop across them turns on the bypass diode across the module (0.7 v). Otherwise the heat produced in the high resistance cells could damage them.

[Pelagic]

Originally Posted by hellosailor

Pelagic, it would appear from Kyocera's "hints" that you have a choice of two evils. Wire the panels in parallel, and you may lose 2-4% all the time because you are providing a lower maximum feed voltage to the MPPT controller. Or, wire them in parallel Series, and you will lose 50% anytime either of them is even partially shaded. (Until Darwin breeds a more intelligent module, yeah.)

Just seems like "parallel" is the clear winner unless your panels will be shade-free 99(?)% of the time. Those 50% output hits have got to outweigh a lot of 2-4% losses, something like 1 hour of any shade would equal 12-25 hours of lower (parallel) output loss, as I see it.

Thanks hellosailor... that seems to be my limited understanding.... and I think I edited what you were explaining correctly.

I am "assuming" that even the shade from 3 or 4 wire stays would be enough to shut down one panel??

1. Guys do we have a consensus then on parallel?
2. Would any of you with experience consider installing on StarGazer's Bimini and not bother building a rack above the tender as a good enough solution to try first?

[bill good]

I am not sure if the cells have bypass diodes across every cell thus bypassing only the shaded cells making series the best option. It may be not so on all panels but it appears that way on mine. I tested for part shading series & parallel before going for series. The sail shades most of the panel anyhow when under way unless you are going the right direction!!

Solar is not the only way & on a boat other means to ensure batteries are topped up must be also planned for.

[cal40john]

Unisolar panels have bypass diodes across every cell, so you only lose the output from that one cell if it is shaded. Amorphous panels ads I have seen have always touted a much better tolerance to shade. I had always assumed that all amorphous silicon panels were made this way, I haven't checked. The drawback with these panels is that they are less efficient. On another thread I did a comparison, IIRC amorphous requires 1.5-2 times the area to produce the same power.

From:
Solar Online Australia - UniSolar 64W Solar Panel US64 12V Amorphous Solar Module

"Bypass diodes are connected across each cell, allowing the modules to produce power even when partially shaded."


I did come across an ad recently that said their new process makes bypass diodes obsolete and increases efficiency, I believe that this was an amorphous panel.


The Kyocera link I posted earlier bothered me because it seemed inconsistent about power loss. So doing more research from this link below I learned that you need at least 1 bypass diode per about 15 cells in series to prevent damage to the panel.
(Nice animations too)
Bypass Diodes

Looking at this Kyocera link
http://www.kyocerasolar.com/pdf/spec...erainstall.pdf

Figure 7 you see there are two sets of bypass diodes. The positive of one set is connected to the negative of the second set and are also connected to what they call the "dummy (non electric)" terminals. I can't see any reason why you need two diode drops for the bypass, but if you assume that the middle of the series connection of the cells of the panel is brought out to a terminal, and that terminal is the dummy terminal, then the one of each of the two sets of diodes are each protecting 18 cells or half of the panel. Going back to the link I posted earlier and now assuming the panel has one bypass diode for each half.

Kyocera | Products | Kyocera Solar Energy | Understanding Solar | Modules

This explains why shading one full cell only reduces the output by half, only half of the cells in the panel are bypassed. It also explains why they show the panel output going to zero when the bottom row is blocked as you have blocked cells in each of the two halves.



Another link:
Electronics - Solar Power Wiring

All large modules have been designed for multiple series connections to accommodate a bypass
diode every 18 cells. This is the principal reason for the dual voltage four terminal output found
on all BP Solar (Solarex) large power modules. The voltage built up across 18 cells is insufficient
to damage a cell even under extreme conditions of temperature and shadowing. Using larger
numbers of cells between diodes allows for substantially more voltage to build up creating more
heat and possibly resulting in module failure under worst case conditions.



So what I had learned before about there being a single bypass diode for a crystalline panel appear to have been either obsolete or incorrect. Instead of losing an entire panel due to shading a cell you will only lose half the panel on a 36 cell module.

John

[ccannan]

BSE MPPT controller models 2512, 1524ix, and the 3024iL are digital.

[Seahunter]

If you shop the discount isle, one gets what you paid for. For panels HIT/HIP (like Sanyo,) technology is the best and shade will never be an issue. The Blue Sky products are reasonably priced but for combining solar as well as wind or other sources there are only a couple of MPPT controllers that handle the job.

[cal40john]

Originally Posted by Seahunter

If you shop the discount isle, one gets what you paid for. For panels HIT/HIP (like Sanyo,) technology is the best and shade will never be an issue. The Blue Sky products are reasonably priced but for combining solar as well as wind or other sources there are only a couple of MPPT controllers that handle the job.

Why is shading not an issue with Sanyo? I see they claim something like 20% more power production per area than other panels, but nothing about shading.

John

[Seahunter]

Sanyo HIT's use an "n" design as opposed to the normal "p" single layering of other panels (you can look it up). This produces over 10% more electricity per panel while Sanyo HIT Doubles employ a double faced hybrid design that work when even covered in snow (by collecting reflected light [as one finds on the water]). HIT technology, although affected slightly by shade still out produce power compared to other makes. Doubles can also be hinged and raised to a vertical position to increase output by another 25-30%. From experience using these panels, the actual ratings are at least 120% over posted performance numbers; unless the "shade" your asking about is a boat shed, I would not worry about it.