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Old 01-01-2012, 09:39 PM   #1
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solar panel sun orientation -

We have a Sprinter PT with fixed roof mounted solar panels under construction. Up here in AK we have lots of summer daylight but the sun angle is very low to the horizon. I see threads about tilting the panel or using portable panels to improve sun exposure for charging. I was wondering - with my limited comprehension of photo voltaic if creating some sort of of adjustable sun reflector for the fixed panels would be easier to manage than making the SP adjustable? Or does it matter with 16-21 daylight hours during camping season - who needs lights, just keep the beer cold? I await wisdom on solar charging - and probably a lot of smilies..
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Old 01-01-2012, 09:49 PM   #2
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Re: solar panel sun orientation -

I really don't know about losses involved, but home systems make tracking panels yet I have never seen a reflector set up to date.
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Old 01-01-2012, 11:18 PM   #3
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Re: solar panel sun orientation -

Take a look at the "Red Book" from the National Renewable Energy Laboratory (http://rredc.nrel.gov/solar/pubs/redbook/). The "State/Territory Data Tables" section shows average solar radiation and the effects of panel tilt, accounting for sun location and length of day.

Besides tilting the panels (which can be a challenge to adjust way up on top of the vehicle), you might consider adding more panels (which you might find easier or less expensive than dealing with tilting).

Either way, I suggest starting with the question "how much power do I need?"
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Old 01-02-2012, 10:59 AM   #4
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Re: solar panel sun orientation -

One problem I foresee with a tilting mirror is the fact that solar panels works best when all cells are equally illuminated. A reflector system would probably leave some cells with less light.

Generally, a panel's output is limited by the cell(s) withe the least output.

So, it would be better to angle the panel.

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Old 01-02-2012, 11:12 AM   #5
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Re: solar panel sun orientation -

In designing a tilt mechanism, keep in mind the impact of shade on panels. The wrong tilt angle will cause one panel to shade another.
Shading even just a few cells will dramatically cut power production. Jage made a great video that demonstrates this point. viewtopic.php?f=14&t=7644&start=15
A lateral tilt is usually preferable to a fore-aft tilt.
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Old 01-02-2012, 11:37 AM   #6
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Re: solar panel sun orientation -

great information thanks guys. Did not know about the JAGE video. I will look into my base load requirements (summer its to keep the frig running and maybe the stereo at times) and the performance of the two horizontally fixed panels that SMB is installing. With the high latitude location I suspect I will need to either supplement the collection area or figure out how to retrofit tilt to the panels if I need more power generation. SMB told me they can add a plug-in for a portable panel and I will have them do that as part of the wiring.
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Old 01-02-2012, 12:21 PM   #7
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Re: solar panel sun orientation -

We've had our van from Alaska to Newfoundland to south Florida. We have a single panel mounted flat on the penthouse roof. Our single 135W panel is plenty to keep the batteries charged, frig (Norcold 12V) running and any entertainment playing. The longest we were parked in any one spot was a week without running the engine. Usually, our batteries are topped up before lunch.

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Old 01-02-2012, 02:14 PM   #8
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Re: solar panel sun orientation -

I tend to agree with Mike in that smaller simpler setups seem to work fine most of the time. Everybodyís usage is different though, and I donít use power in camp (other than the refrigerator) during the day so YMMV.

One exception for charging is being in an area with constant overcast skies, and usually more solar doesnít help as much as something constant like a generator.

I have 2- 220 Ah 4-D house batteries and sized the solar to that along with my load. With 2-135W panels, I can be charged up by 9AM for the most part. While sitting in fog, I usually have enough to keep the refrigerator running without battery drain. I donít think tilting the panels would help in a foggy situation and I even wonder if more solar would be worth taking up roof space. I carry a 65w flat panel but have rarely used it.

Where a tilting or spare panel would help is being in cover but sun is coming through the trees that you can get some (flat) sun to the panel.

Besides, Iím lazy and feel it would be a PITA to deal with climbing up just to pull an extra amp or two.
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