Solar Panels 'flat' on roof??

What's the efficiency of having solar panels mounted horizontal on the vehicle roof?? I would imagine that it would only give maximum performance at around midday- during Summer.
Also notice some mounted on the roof front, at about windscreen angle. This would be great travelling in a Northerly direction- what happens when you head in a Southerly direction??
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Reply By: Battery Value Pty Ltd - Thursday, Apr 08, 2010 at 11:39

Thursday, Apr 08, 2010 at 11:39
Hello Signman,

for a solar panel mounted on a vehicle which constantly changes directions, it's a no brainer to put it flat on the roof.

The only way to improve the solar output in such a situation is to have the panel mounted on a 1 or 2 axis solar tracker.

But the power gain from the panel when doing this will most likely be gobbled up by the added wind drag of a tilted panel, and by the tracker motor(s).

So keep it flat while travelling, and tilt it at latitude angle and make it facing north when stationary.

Best regards, Peter
AnswerID: 412102

Follow Up By: _gmd_pps - Thursday, Apr 08, 2010 at 12:01

Thursday, Apr 08, 2010 at 12:01
I originally planned for 300W and the fact that I did not want any complications from changing angles or sun tracking I decided to go for 400W and keep it flat.
I have made a frame which is bolted to the sides and not to the roof which gives me good stability for the large panels as well as airflow underneath and no risk of ripping holes into the roof on corrugations. By the way in Europe they glue the frames to the roofs .. no screws anymore .. but I would not trust that with my panels weighing 22kg each .. on corrugations everything will shake loose eventually.
good luck
gmd
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Follow Up By: Member - Willie , Sydney. - Thursday, Apr 08, 2010 at 12:33

Thursday, Apr 08, 2010 at 12:33
Gday Peter,
Back from Tassie I see. When can I come around to have the black stuff put on my windows ?
Thanks,
Willie.
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Follow Up By: Member - Willie , Sydney. - Thursday, Apr 08, 2010 at 15:23

Thursday, Apr 08, 2010 at 15:23
Peter ? Am I loosing it ? Sorry.
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Follow Up By: Battery Value Pty Ltd - Thursday, Apr 08, 2010 at 15:30

Thursday, Apr 08, 2010 at 15:30
there is only one Peter posting in this thread I know of :P
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Reply By: Mandrake's Solar Power- Thursday, Apr 08, 2010 at 12:13

Thursday, Apr 08, 2010 at 12:13
Signman ,

Yep correct the 3 hours around midday would be the max - after that the input would drop off rapidly until sunset when almost nil.....

I have a 140 watt mounted flat on the Jeeps roof rails and it runs a 100 aH AGM which in turn runs my Waeco 50 - If I get 4 cloudy days in a row I need to get to 240v pretty quick to top up the battery - If its sunny days then no problems --
I don't have a dual battery setup yet and so far ( touch wood ) haven't really needed one ... However the Kimberley trip next year will cause me to fit one before leaving I think...

Cheers

Steve
AnswerID: 412108

Follow Up By: signman - Thursday, Apr 08, 2010 at 12:30

Thursday, Apr 08, 2010 at 12:30
And it's around midday we're looking for a shady tree to park under for lunch !!
Not really conducive for Solar Energy collection !!



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Follow Up By: Maîneÿ . . .- Friday, Apr 09, 2010 at 18:06

Friday, Apr 09, 2010 at 18:06
signman,
with solar power, fortunately by "midday" the battery bank is again fully charged.

If it was a generator (Yammie / Honda etc) when the battery bank is fully charged you have to be there to go and turn the generator off, you don't let it run all day for very obvious reasons.

With solar power it is exactly the same, however the solar regulator does the "turning off" (in a figure of speech) for you, you don’t have to be there to do anything.

Maîneÿ . . .
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Reply By: Neil & Pauline - Thursday, Apr 08, 2010 at 12:32

Thursday, Apr 08, 2010 at 12:32
There is a formula for the losses from flat as against angled. It is much cheaper to add more panel watts than make angular from my enquirers.
I have mine flat and no problem. just need to work it out before you start.

Neil
AnswerID: 412110

Reply By: Fatso - Thursday, Apr 08, 2010 at 12:34

Thursday, Apr 08, 2010 at 12:34
I know a bloke that had solar panels mounted on an aluminium rack on his car. The rack sat flat, but with the pull of 2 spring loaded latches the panels would lean forward to 15 deg or whatever the optimum is. He had gas struts set to get the right angle. He also had an in-car compass to ensure he could park facing North.
He had a battery in the van & a couple in the back of his ute & a fair length of lead to join the solar panels & bank in the car to the van.
It is one of the best set-ups I have seen. But wasn't cheap
AnswerID: 412112

Reply By: Mike DiD - Thursday, Apr 08, 2010 at 12:49

Thursday, Apr 08, 2010 at 12:49
Why worry about Solar Charging when you're driving - a Panel puts out 5 amps - your Alternator can put out 50 amps at least !
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Follow Up By: get outmore - Thursday, Apr 08, 2010 at 13:12

Thursday, Apr 08, 2010 at 13:12
nooooooo - youll wake Mainey up
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Follow Up By: Maîneÿ . . .- Friday, Apr 09, 2010 at 00:40

Friday, Apr 09, 2010 at 00:40
yes, tis true :)

Maîneÿ . . .
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Reply By: Member - Brian (WA) - Thursday, Apr 08, 2010 at 13:33

Thursday, Apr 08, 2010 at 13:33
Hi I have mine flat on the roof. They are also hinged so I can raise them to 45deg if I need to catch more sun in the PM when stopped. I also plug the
Engel's into the car when travelling.
Brian
AnswerID: 412120

Follow Up By: Member - steve. B... (NSW) - Thursday, Apr 08, 2010 at 15:01

Thursday, Apr 08, 2010 at 15:01
My 80 watt panel is bolted flat on the roof of the Tvan. Ran the Fridge/freezer/Lights off the 100 a/h deep cycle for ten days with no problems.
Although it was sunny most of the time. Steve.B...

Lifetime Member
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Reply By: Nomadic Navara - Thursday, Apr 08, 2010 at 16:52

Thursday, Apr 08, 2010 at 16:52
Whilst panels may loose quite a bit of output at midday when lying flat as compared to the correct angle, you can not use this to calculate the efficiency drop over the whole day. In the morning and afternoon flat mounted panels will put out more than they do when elevated in the optimal position (particularly when the sun is below the east/west line.) Thus they do not loose as much output when mounted flat as they appear to if you only look at the midday results.

As suggested previously in this thread - just increase the size of your panel(s) a little. That will be cheaper and less fiddly than providing moveable mountings or trackers.
PeterD
Retired radio and electronics technician

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AnswerID: 412142

Reply By: Member - Barnray (NSW) - Thursday, Apr 08, 2010 at 20:41

Thursday, Apr 08, 2010 at 20:41
I have 2*80 watt panels mounted on a tripod with a suntracker system. They are rated at 4.5 amps delivery each, with the tracker I can get 9.3 amps from both all day while the sun is out and if the sky is overcast and thin it will lock onto the brighter areas and still produce up to 3.5amps. Its a bit difficult to use on the move but if you have about 40_60 amps from the alternator you don't need solar. Barnray
AnswerID: 412171

Reply By: Maîneÿ . . .- Friday, Apr 09, 2010 at 00:51

Friday, Apr 09, 2010 at 00:51
signman,
It depends on the performance characteristics of the panels, some will work much better in low light conditions than some others and therefore they also start delivering current into the battery much earlier than the less efficient panels, this gives you much better battery charging overall.

My system gives 100% of it’s rated output before 11.30am even when laying horizontal on the roofrack.

Maîneÿ . . .
AnswerID: 412216

Follow Up By: oldtrack123 - Friday, Apr 09, 2010 at 16:37

Friday, Apr 09, 2010 at 16:37
Hi Signman

Although Mainey refuses to accept it, his panels ,like all panels in full sun, put out near max amps but not max rated watts .
His panels ,like all panels, are about 85% efficient

See this thread
http://www.exploroz.com/Forum/Topic/77244/SOLAR_panel_effiency_-_debunking_myths.aspx?ky=&p=%2fForum%2fDefault.aspx%3fpn%3d13
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Follow Up By: Maîneÿ . . .- Friday, Apr 09, 2010 at 17:51

Friday, Apr 09, 2010 at 17:51
I'm prepared to accept any thoughts at all, only when they can be shown to be factual.

Now you have that opportunity to state, what you believe, to be the facts as you see it, the thread you elude to does in fact state my system is putting out "max rated watts" by the panel manufacturer.

Maîneÿ . . .
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Follow Up By: Maîneÿ . . .- Friday, Apr 09, 2010 at 20:22

Friday, Apr 09, 2010 at 20:22
oldtrack,
the link did not work for me so I will repost it for you again, as I just read it
SOLAR panel effiency - debunking myths ?
It is now locked

Thread number: 77244

Maîneÿ . . .
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