Solar Panel Combinations and Orientation Options

[JPA Cate]

Matt,

If you buy new panels in which each cell has a bypass diode, my "resident expert" says that will give you the most output, as they are the least affected by shading. Life isn't perfect. But, you know, you might consider putting on a stern roller, so you could anchor by the stern in northerly condx, to expose the solars! :O They're just part of the total picture, and some seasons are better than others, and some passages, ditto.

I'd go with two, but I'd try really hard to make them somewhat adjustable, to take the best benefit of the sun whenever possible. PS, for sailing and docking, I really do not like them overhanging the boat. I see that they will, but those corners hanging out are just waiting to get snagged on something.

My two cents'..... And remember sailorchic's an engineer and can be presumed to know more about the technical end of this than I do.

Ann

[GILow]

Originally Posted by Ann T. Cate;1609620.

I see that they will, but those corners hanging out are just waiting to get snagged on something.

Good point , thankfully however, they won't stick out as far (sideways or aft) as the davits on the stern, which is a good thing. I left the davits out of the picture as they are well below the panels (thus not likely to shade them even down here in the Southern hemisphere) and so only confused the picture.

Canoe stern boats are a bit of a pain for this sort of thing though. I was looking at a Catalina 42 near my boat and they had ACRES of space for their panels. A much broader backside.

Matt

[GILow]

Originally Posted by Ann T. Cate

If you buy new panels in which each cell has a bypass diode, my "resident expert" says that will give you the most output, as they are the least affected by shading.

Please thank your "resident expert" for me. (when he has finished swabbing the decks, cooking the tea and scraping the bottom of the boat.) The Kyocera panels have the diodes in question.

Matt

[socaldmax]

Originally Posted by GILow

OK, look, thank you for the suggestion, but it is not really answering my question.

Sorry if that sounds narky , but really, I don't want to move all that stuff, I am very happy where it is.

It is a well thought out arrangement that was designed with safety and practicality foremost, unfortunately, this put the efficiency of the solar lower down the priorities (I suspect the solar was very much an after-thought, years after the event as it were.) All in all, I am happy with that order of priorities.

I accept that it is not ideal, but what I am trying to figure out if two 140s or four 70s are going to be the "least worst" solution.

Matt

Perhaps you didn't read the part where I wrote "2 140 watt panels." Was that somehow too ambiguous?

For the record, I fail to see how a stern mounted radar is the optimum location for safety. The mast is at bearing 000 and gives you a blind spot right at that bearing. To me, the optimal location for a radar is as high as possible on top of or on the leading edge of the mast. This gives more range and contacts coming from behind will be closing at a slower rate than contacts that you're sailing toward, giving you more time to see them visually.

I think you meant "most convenient" location.

[noelex 77]

Originally Posted by GILow

The Kyocera panels have the diodes in question.

All reasonable quality solar panels have bypass diodes. The Kyocera panels have more than most. There are 8 bypass diodes in most of their 36 cell panels.

To answer the OP's question the 4x70 watt combination is likely to give the most output (even though the orientation is not ideal), but the difference will not be great. Other factors such as ease of installation, cost etc are probably more important given that there will only be a small difference in output.

[Snowpetrel]

Another small factor, but worth considering is the possibly of damage, I had one of my two 40w panels die coming home from antarctica. It cut my power by more than half. If I had four it would not have been a problem. Smaller ones are often stronger as well, so might survive a halyard shackle impact. Or naughty kid throwing stones! But this is all balanced by higher cost and more complex wiring with more to go wrong.

I've been toying with the idea of a swinging radar and windgen mount that can be rotated away from the panels. Another Tig project!

[GILow]

Originally Posted by socaldmax

Perhaps you didn't read the part where I wrote "2 140 watt panels." Was that somehow too ambiguous?

For the record, I fail to see how a stern mounted radar is the optimum location for safety. The mast is at bearing 000 and gives you a blind spot right at that bearing. To me, the optimal location for a radar is as high as possible on top of or on the leading edge of the mast. This gives more range and contacts coming from behind will be closing at a slower rate than contacts that you're sailing toward, giving you more time to see them visually.

I think you meant "most convenient" location.

Well, no, not the most convenient, actually. The most well thought out.

There is no blind spot that matters, radar wraps around the mast from that range quite easily (see the wave model of EM radiation for an explanation.) The radar is well clear of the mast where it is, so this minimises the chance of a blind spot in any direction, which is kind of academic on a sailing boat anyway since they are wobbling all over the place as they travel.

Meanwhile the radar is well clear of any critical rigging such as halyards, which time and time again seem to get fouled on mast mounted radars. It is also low enough to minimise its contribution to rolling momentum, not the case on a high mast mounted unit.

Yet again, I feel that the guy who set the boat up was really thinking things through.

And thank you, I did see your comment about two panels but I was not clear on your reasoning for it so I was not sure how to apply it to my dilemma.

Anyway, thanks for the comments.

Matt

[GILow]

Originally Posted by noelex 77

All reasonable quality solar panels have bypass diodes. The Kyocera panels have more than most. There are 8 bypass diodes in most of their 36 cell panels.

To answer the OP's question the 4x70 watt combination is likely to give the most output (even though the orientation is not ideal), but the difference will not be great. Other factors such as ease of installation, cost etc are probably more important given that there will only be a small difference in output.

Noelex77, thank you for that response. I am not sure where I got the idea that maybe 4 smaller panels might be more resistant to problems, but I wondered if you had posted such a suggestion on another thread?

Fortunately, the installation is easy either way, and the cost difference was minor, so combining your logic with Snowpetrels good point about minimising damage impact, I am favouring the four smaller panels.

But I have bought a significantly larger capacity MPPT regulator, just in case my logic proves to be totally flawed, I can then add panels to the cabin roof. (I took those off to make it easier to work on the main sail from the cabin roof.)

Here's to not nursing every electron on the boat.

Matt

[socaldmax]

Noelex77, I'm curious why 4 70 watt panels would out produce 2 x 140 watt panels. I figured fewer connections (possible points of failure, especially in a marine environment) and higher output per sq meter with the 140 w panels would be the desirable attributes on a boat, where space is at a premium.

If I were anticipating damage from falling objects, then the loss of a 70 watt panel (removed from the circuit) would be better than the loss of 140 watts, I've just never seen that as a deciding factor in panel selection before. It might actually be an argument for carrying a spare panel onboard, possibly a spare solar controller, depending on how far from civilization you plan on travelling.

Something that hasn't been mentioned is the voltage of the panels vs the max input voltage of the solar controller. I have a SB2000e 25 A controller that cannot take any higher than 24v, a lot of newer panels are higher than that. If one has 37 Voc panels for example, and one has a 70v max input solar controller, you're still limited to having the entire array in parallel, which eliminates the possible power savings of running in series @ 74V through the provided cabling.

Since you didn't mention your battery bank voltage, I'm assuming it's a 12v bank, but that also has a bearing on which controller to buy, especially in the case of 24 or 48 v battery banks.

At any rate, let us know how well the system works once installed. Math is one thing, actual performance is sometimes a little different. I have 2 x 155 w panels mounted too close to the roof A/C of an RV. It shades the bottom approx. 2" x 10" of each panel, but that's enough to drop output from a theoretical max. of 18 A to around 8 -9 A, sometimes a little less shading produces 10-12 A. The best I've ever seen with no shading is 15.5 - 16 A, this is with the SB 2000e MPPT controller and very large cabling.

[tomfl]

I would go with the four panel option but I am not sure there will be a big difference in power. First off any shadows falling on the panels will be so random that it is really almost a crap shoot guessing how that will decrease the output. Another thing I have noticed is that in theory as the panels get warmer output decreases. Last time I shot an infrared gun at the bottom of my panels the temperature was 130 degrees F, but that was in August in the hot Florida sun just before high noon. I have seen claims that the decrease in output from high temperatures is so great that upgrading to the latest and greatest is not really worth it from a bang for the buck analysis.

Best of luck what ever you do.

[GILow]

Originally Posted by tomfl

Another thing I have noticed is that in theory as the panels get warmer output decreases. Last time I shot an infrared gun at the bottom of my panels the temperature was 130 degrees F, but that was in August in the hot Florida sun just before high noon. I have seen claims that the decrease in output from high temperatures is so great that upgrading to the latest and greatest is not really worth it from a bang for the buck analysis.

Best of luck what ever you do.

Tomfl, heat is a real issue for us here in Adelaide. On the odd 45 degree (Celsius) that hits Adelaide, our 2KW roof array really drops in output, close to 20% less output than on a 30 degree day.

Thankfully the installation of these panels will be close to ideal for heat dissipation, as they are completely free-standing, no surfaces of significant size anywhere nearby.

Separate to all this, your point about the latest and greatest is well made, and I am currently sorely tempted by some el-cheapo alternatives, on the simple logic that by the time we get to use the boat properly, any very good quality panels will already be starting to degrade in performance, maybe only slightly... but still.

Perhaps some cheap panels in the interim....

Matt

[Ex-Calif]

Hmmm...

2 X 140s and one panel gets some shade on it's end - It drops the output say by 50% on that panel. You still have 75% output.

4 X 70s and one panel gets shaded and the output on that panel goes to zero. You still have 75% output.

I am sure someone out there has done some testing and posted YouTube about it.

However it sounds like you are resigned to having shaded panels.

The other consideration is panel density vs. space. Each panel has an "edge" structure. 2 panels will have more cells per square feet vs. 4 panels.

I'd go with 2 just for that reason. And if performance is poor you know the reason. Shading.

[tomfl]

I would not go with an el cheapo option, but not go bleeding edge either. I have some nice Evergreens on my boat, suppose to have around 18% efficient. Some of the new ones are claiming around 20% but that is under ideal conditions.

My comment about shading was that the shadow is irregular in shape and it is just a guess about how much of a hit the power output will take. The more dense array on larger panels means the same size shadow would cause a bigger hit, all else being equal. Problem is I am not sure all else is equal.

If I was replacing my panels I would go with some type of folding or flexible design. While there is a hit in the output they are much lighter and reducing weight aloft, even if it is only ten feet off the deck seems like a good idea to me. Also suspect it would be easier to adjust the lighter panels to get a more direct hit from the sun.

[SailFastTri]

Sorry for double post- it was a database error on this site

[SailFastTri]

Originally Posted by Ex-Calif

Hmmm...

2 X 140s and one panel gets some shade on it's end - It drops the output say by 50% on that panel. You still have 75% output.

4 X 70s and one panel gets shaded and the output on that panel goes to zero. You still have 75% output.

Snip.

You're assuming he wires them in parallel. For the best output he should take advantage of the MPPT controllers' ability to do voltage conversion. This would dictate that the 2 X 140s would be wired in series, or the 4 X 70s be connected in series-parallel as two pairs. In that case he effectively has two logical panels, or one logical panel (from an electrical perspective).
If unshaded, this higher voltage would reduce wiring losses and give the MPPT controller a huge performance boost by allowing it to operate in more efficient ranges for more hours per day (and in lower light when it's a bit overcast).
I have 8x20w panels and have tested both ways (parallel vs. series/parallel) and while I can't put a precise number on it the difference in the real world is huge (perhaps 50% improvement).

Note: corrected above to "parallel vs. series/parallel"