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Old 10-04-2021, 00:28   #1
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Solar Panels - horizontal or angled?

Which of the two solar panel arrangements in likely to be more effective in general.???

Both have the same area (3 sq m). Arrangement 'A' is completely horizontal (at rest) where as arrangement 'B' has 1.5 sq m horizontal and two 'wings' each 0.75 sq m) angled (fixed) say 45 degrees (or maybe 30 degrees) from horizontal.

Assuming a mono hull, aligned fore and aft as shown, no shading from rig etc, used both underway and anchored, used at any latitude from 0 to say 45 and each panel has its own MPPT charge controller.
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Old 10-04-2021, 00:53   #2
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Re: Solar Panels - horizontal or angled?

In arrangement B, if the sun is to one side can the opposite side be a tilting panel that could be moved to the horizontal otherwise it is going to be facing away from the sun.

Mine do slope slightly forward, not to catch the sun though, but so the rain runs off the panels, also the soapy water when you clean them.

The difference between flat and tilted towards the sun is huge and the reason why I used to move our portable suitcase panel around the yacht several times a day. The latest panel is just too big to do that and I really don't want to put any twist in the panel when changing its orientation. Cracking the glass wouldn't be a good day on the boat.

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Old 10-04-2021, 01:57   #3
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Re: Solar Panels - horizontal or angled?

It would be nice to see some experimental results for this and other similar questions, but after many years living on boats with both fixed and tiltable solar panels and watching the battery monitor far more than is really needed, my estimation is that A would win by a considerable margin.

B has the advantage that it takes up less projected surface area, so for example it would fit on a narrower stern.
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Old 10-04-2021, 02:21   #4
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Re: Solar Panels - horizontal or angled?

There is one yacht that has sloppy panels at the sides and that is Free Range Sailing. They are both quite clued up and live a minimalist lifestyle. I followed their hard dodger build with interest.

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Old 10-04-2021, 02:45   #5
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Re: Solar Panels - horizontal or angled?

Insolation tends to peak when the sun is at the zenith and to loose intensity as the angle lowers. Thus it seems to me that tilting the panels reduces the theoretical input as the tilted panel is normal to the radiation (best absorbtion) during a period when the available energy is less than at noon. And of course the one on the "other" side looses bigtime!

Being able to track the sun angle, even in a gross sense (like three times a day) will make noticeable increments in the totals accumulated each day. On our previous boat we could do this, and it really helped.

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Old 10-04-2021, 04:09   #6
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Re: Solar Panels - horizontal or angled?

I think any gain of one sides angled panel will be offset by a loss on the other angled panel. At best it will just equal out. Meanwhile the angled panels lose sun during the peak hours.

My vote is go flat.
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Old 10-04-2021, 04:18   #7
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Re: Solar Panels - horizontal or angled?

There is also large seasonal and latitudinal (?) variation in sun angle, so a lot depends on where you are. If you size the array and loads for year-round use, you will have lots of excess capacity in the height of summer, so small differences like this really won't matter at all.

For example, we have rail mounted tiltable panels and a bimini array. In winter, just one of the rail panels (depending on wind direction) will provide nearly all our energy while the bimini panels barely contribute because of the low sun.

If this is your case, you might want to think about making the two wings pivot. I made ours to only provide 0, 45, and 90 degrees which was a pretty simple proposition.

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Old 10-04-2021, 04:24   #8
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Re: Solar Panels - horizontal or angled?

If you can change the angle of the panels in Option B to optimize exposure, then that would likely be the potential winner. But if they are static at a given angle, then I'd say you'd be better off with horizontal presentation.

My current setup includes 1/4 of my wattage being on hinged panels that can track the sun's ascending or descending angle. It does make a difference, but only for a short period each day. I've never tried to figure out the added amps I gain by doing this, but overall it is small. And it's at the cost of manually changing the angles over a relatively short period -- something I find myself doing less and less.

When I install new panels I'll be sticking with straight horizontal layouts. Simpler, and nearly as efficient.
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Old 10-04-2021, 05:04   #9
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Re: Solar Panels - horizontal or angled?

I think the answer to your question will depend on what you are aiming for; whether you want to maximise Ah input or maximise charging time.

Horizontal panels will probably (I don't have numbers to support this I'm just guessing) give maximal Ah power generated per day, but realistically you want to have enough solar that actually your batteries are already out of bulk charging stage before the sun is very high, in which case all that excess capacity is wasted. In our case:

We have more solar than we really need. Max current at mid-day isn't valuable to us, so we angle the panels. We start charging earlier in the day and finish charging later in the evening. This results in overall lower depth of cycling and longer battery life.
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Old 10-04-2021, 08:09   #10
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Re: Solar Panels - horizontal or angled?

I tend to go with the age old adage of KISS, Keep It Simple Simon.

So my panels are secured to the top of my bimini horizontally where I can (generally) keep them out of the worst of the shade. Yes I lose some amps in the morning and evening but the vast majority of useable power is from around 10am to 4pm where I sail and he small difference between tilting to the perfect angle and just keeping them out of the shade of the boom or mast is negligible in the overall scheme.

My flat 100w panel still gives me around 6amps in full sun so it's not worth, to me, the effort to tilt or orientate it all the time.
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Old 10-04-2021, 08:37   #11
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Re: Solar Panels - horizontal or angled?

This is a mental game with, for a mobile installation, far too many variables. I suspect this is closest to the truth....
Quote:
Originally Posted by sailorboy1 View Post
I think any gain of one sides angled panel will be offset by a loss on the other angled panel. At best it will just equal out. Meanwhile the angled panels lose sun during the peak hours.

My vote is go flat.
Take a Milk Run trip. At anchor the boat is generally pointed E/SE and underway generally W. We make these trips in the “winter” to avoid cyclones, so the sun is well north. With the boat generally facing E or W the angled panel on the north side of the boat will out-produce the flat panels, but the angled panel on the south side will under-produce.

If the sun elevation is above 45* then the maximum gain for a panel normal to the sun vs. a horizontal panel is about 30% (normal panel at 100% production vs horizontal panel at sin(45)=70%). The loss from the panel opposite the sun, if shaded by its brothers, could be 100%.

If the boat is generally pointed N/S, however, the scenario is different throughout the day, but one angled panel will always produce less and one more.
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Old 10-04-2021, 08:47   #12
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Re: Solar Panels - horizontal or angled?

Quote:
Originally Posted by Pete7 View Post

clip...

Mine do slope slightly forward, not to catch the sun though, but so the rain runs off the panels, also the soapy water when you clean them.

clip...

Pete
and

Quote:
Originally Posted by Mike OReilly View Post
If you can change the angle of the panels in Option B to optimize exposure, then that would likely be the potential winner. But if they are static at a given angle, then I'd say you'd be better off with horizontal presentation.

My current setup includes 1/4 of my wattage being on hinged panels that can track the sun's ascending or descending angle. It does make a difference, but only for a short period each day. I've never tried to figure out the added amps I gain by doing this, but overall it is small. And it's at the cost of manually changing the angles over a relatively short period -- something I find myself doing less and less.

When I install new panels I'll be sticking with straight horizontal layouts. Simpler, and nearly as efficient.
Sunpower is the leader in efficiency...

They recommend installation, even in the tropics where horizontal could reasonably be appropriate for a fixed installation, be with a minimum 10į deflection, for the reason highlighted in the first quote, and for self-cleaning in general.

The second quote's highlight is to note that unless you have a very expensive automated sun-following array, and/or are willing to babysit flexibly oriented panels, it's all academic.

In our installation, the arch fabricator blew it, and rather than start over, said he "liked the way it looked better" - a source of some very annoyed moments - but it wasn't going to be changed, come hell or high water.

As it turned out, the forward facing slope of probably a bit more - but not much - than 10 degrees was a very good thing. And, as our mount is VERY robust, it also means that I'd not (and didn't, in two Cat2s) worry about their security in a hurricane, as the force of the wind is downward (they're rated for Cat5 pressures). Note that both were on moorings; the premise is that the wind would come from the bow orientation regardless of what phase of the hurricane presented...

So, to the original question/post:

Nearly all of the responses are correct. If you need to limit width but have the most possible wattage, the sides will work better alternately as the boat or sun moves. But your other side will suffer.

Left alone, as most would be, other than perhaps to raise them from a vertical position as you travel, it evens out.

But having some slope is useful for keeping them clean...

You can see our installation/upgrade to 360W panels, here, for illustration:

Pictures: Flying Pig 2015-2018 Shake-and-Break-Down/Electrical Upgrade/Solar
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Old 10-04-2021, 08:57   #13
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Re: Solar Panels - horizontal or angled?

Quote:
Originally Posted by Dsanduril View Post
If the sun elevation is above 45* then the maximum gain for a panel normal to the sun vs. a horizontal panel is about 30% (normal panel at 100% production vs horizontal panel at sin(45)=70%). The loss from the panel opposite the sun, if shaded by its brothers, could be 100%.
The atmosphere scatters a good portion of the incoming sunlight. Therefore the sun cannot be considered a point source of light and solar panels produce significantly more power when the sun is at low angles than simple trigonometry would suggest.
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Old 10-04-2021, 09:34   #14
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Re: Solar Panels - horizontal or angled?

Quote:
Originally Posted by noelex 77 View Post
The atmosphere scatters a good portion of the incoming sunlight. Therefore the sun cannot be considered a point source of light and solar panels produce significantly more power when the sun is at low angles than simple trigonometry would suggest.
Agreed, especially on/around water. It was a simplified example just to point out the huge number of variables. Especially at lower sun angles the scattered and diffuse contributions can be quite significant.

In the example presented though, given the OP’s sketch, the south facing panel will almost certainly be shaded by its friends to the north. And reflected light will generally be headed south, leaving only some (generally) weak diffuse light to hit that panel.
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Old 10-04-2021, 09:47   #15
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Re: Solar Panels - horizontal or angled?

Quote:
Originally Posted by Wotname View Post
Which of the two solar panel arrangements in likely to be more effective in general.???

Both have the same area (3 sq m). Arrangement 'A' is completely horizontal (at rest) where as arrangement 'B' has 1.5 sq m horizontal and two 'wings' each 0.75 sq m) angled (fixed) say 45 degrees (or maybe 30 degrees) from horizontal.

Assuming a mono hull, aligned fore and aft as shown, no shading from rig etc, used both underway and anchored, used at any latitude from 0 to say 45 and each panel has its own MPPT charge controller.
Your question is purely theoretical in which case those angled at 90 degrees to the sun will work the best; horizontal or vertical doesn't matter.

Practically speaking the biggest drawback of installing solar on a monohull sailboat is finding a suitable place for the installation. The next question is how many watts can you get installed, the more the better. The last question I was concerned with was the angle of the panels (actually I wasn't). Why? Because its a monohull sailboat moving with the wind where the wind angle for the sails is more important than the sun angle for solar while contending with the ever changing heel of the boat.

I installed 4x140W (560W) solar panels on my boat in 2015; two on top of the dodger and two on top of a new stern arch. Those on the arch get the full sun most of the time while those on top of the dodger generally get about half use but in reality it all depends on the boat's course and the angle of the sun. By the way the panels on the arch (horizontal) are angled a tad to the stern to drain rain water and bird droppings overboard; those over the dodger (horizontal below the boom) are both angled to the dodger port/starboard edges following the curvature of the dodger; installation practicality took precedence over their angles.

Prior to my installation I corresponded with a cruiser in the Pacific and he recommend getting as close to 600W as possible and that was my driving creed in the installation...that was good advice and it has worked fine for me.

So succinctly, install as much solar as you can and don't sweat the panel angles...unless your a liveaboard and/or never sail the boat.

~ ~ _/) ~ ~ MJH
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