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Old 01-11-2009, 11:03   #1
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Solar Panel Question: Angle of Sunlight

How much does the angle of the sunlight hitting the solar panel effect the output of the panel(s)? I just mounted a little "trickle charger" panel on my sail dinghy, I mounted it horizontally, so as to catch sun rays from all angles, that seemed to be the best way to assure that it would catch some sun no matter the direction the dinghy is facing.
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Old 01-11-2009, 11:10   #2
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Photvoltaic Modules - Solar Panel FAQ.
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Old 01-11-2009, 11:46   #3
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To calculate the best angle of tilt in the winter, take your latitude, multiply by 0.9, and add 29 degrees. The result is the angle from the horizontal at which the panel should be tilted.
The optimum angle of tilt for the spring and autumn is the latitude minus 2.5̊.
The optimum angle for summer is 52.5̊ less than the winter angle.
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Old 01-11-2009, 11:53   #4
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Would I be better off trade catching light no matter the direction of the boat or mounting at the best angle to optimize the panels output when it is catching the sun?
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Old 01-11-2009, 12:04   #5
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In general terms, the output of your panel will be reduced from its maximum (the sun being perpendicular to tha panel surface), by the cosine of the angle from perpendicular. Here are some numbers:
0 deg (perpendicular) = 100%
30 deg = 87%
45% = 71%
60% = 50%

Note that 100% is not necessarily the rated output of the panel, and will usually be less, depending on the temperature, time of day, the season, and your latitude. Also, some panel designs are better at capturing the off-axis light, but others will not do as well as shown for the large angles.

I think that unless you can control the orientation of your boat, you may as well orient the panel horizontally. Also, even the non-optimum orientation may give you all you need in your trickle charge application.
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Old 01-11-2009, 12:14   #6
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No expertise here, but I've heard of sailors mounting solar panels nearly vertical in order to catch both the direct sun and the sun reflected off the water. Is there any validity to that approach? I was surprised by the implication that the reflected sunlight could be a significant contributor to the overall power output.
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Old 01-11-2009, 12:50   #7
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Optimizning solar panel charge potential

We have four solar panels, mounted in 2 pairs on masts at the end of our hulls. We can rotate them on a horizontal or a vertical axis. I notice a big difference in charge rate when they are oriented at about 90 to sun angle. I also note that best charging time in the tropics is usually in the morning. Often in the afternoons you get the clouds building up and rain. So if you can mount your panel so it is secure yet can still move to a good sun angle, you’ll get a lot more from it.

Cheers!
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Old 01-11-2009, 13:13   #8
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keep facing the sun

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No expertise here, but I've heard of sailors mounting solar panels nearly vertical in order to catch both the direct sun and the sun reflected off the water. Is there any validity to that approach? I was surprised by the implication that the reflected sunlight could be a significant contributor to the overall power output.
This wouldn't work. The reflectivity of water is close to 100%, but only if angle of incidence is 0 degrees (i.e. the sun is directly overhead). The reflectivity drops rapidly as the angle increases. So if the sun is at 45 degrees, less than 5% of the sunlight is reflected off the water surface.
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Old 01-11-2009, 13:26   #9
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My solar panels are attached flat above the bimini. It is not the most efficent, but is a good comprimise. Before 7am I start charging and hit the max of 30 amps between 10 and 2. From there it declines to zero at about 6pm. This is presuming no clouds and is at 12 degrees latitude.

If you have the time to aim them right at the sun, you will increase the charge significantly. However, if you forget to reaim you will not get any better than my static array. Personally I have better things to do then try to find the optimal angle, especially when on the hook.
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Old 01-11-2009, 13:34   #10
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Well, thanks for all the feedback / advise. Being that this is just a sail dinghy that will be on the hook in an anchoring field and the only electrical usage when I am not on the boat will be the bilge pumping system, which should only draw about 4.1 AH, I think I will stick with the horizontal mounting. According to the specs for my panel it should replenish the battery at a max rate of .75AH which I am thinking SHOULD cover the power needs of the pumping system.
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Old 01-11-2009, 13:48   #11
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Quote:
Originally Posted by kcmarcet View Post
Would I be better off trade catching light no matter the direction of the boat or mounting at the best angle to optimize the panels output when it is catching the sun?
As you've already concluded - yes.
It's not the most efficient solution, but certainly the most practical, in your application.
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Old 01-11-2009, 14:13   #12
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Put it on a swivel if you have that mounting option. Move the panel around and see at what angle its producing the most current for a given course and sun altitude. That's the bottom line. If you don't have the swivel option then mount it so it gets the maximum light out of 360 degrees.
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Old 01-11-2009, 17:24   #13
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Would I be better off trade catching light no matter the direction of the boat or mounting at the best angle to optimize the panels output when it is catching the sun?
Westwards. Interesting thing recently where an architect put most of his house pannels on hit western facing roof to get the afternoon sun. He had worked it out that its better than north/south facing (hemisphere) or east facing for morning sun.

So unless you are in a tropical area which generates afternoon clouds then angle more to the west than east.
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Old 01-11-2009, 18:07   #14
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a different approach

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Put it on a swivel if you have that mounting option.
I built a hard bimini out of solar panels, all of which are horizontal all of the time. While I realize they are not at peak efficiency other than at noon, I have enough wattage up there to do the job except in serious fog. Nice thing is that I never have to worry about swiveling the panels when the tide turns.
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Old 01-11-2009, 18:48   #15
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Good choice. Seems like its easier to have more laying flat than to have one or two that must be kept pointed in an optimal direction.
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