Solar panel on roof

Submitted: Saturday, Mar 13, 2004 at 18:01
ThreadID: 11219 Views:2160 Replies:7 FollowUps:15
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Interested in installing a 60W -80W solar panel on the roof rack of my Cruiser.
Have read other threads with good advice on regulators, size ,etc.
My question is how strong and resistant to damage are they on the rof rack - will they resist the odd stone, branch etc. that one encounters.
Many thanks,
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Reply By: KiwiAngler - Saturday, Mar 13, 2004 at 19:45

Saturday, Mar 13, 2004 at 19:45
The only 'down side' to permanently affixing the panel to the roof is that you will either miss out on a lot of the potential suns power, due to not having it correctly aligned or have to move it around a bit.

If I recall, someone on the forum has done some work on this topic and posted just how few a number of hours you would get from a permanetly fixed unit vs one that you can move. There was quite a big difference.
AnswerID: 50209

Follow Up By: Brad - Saturday, Mar 13, 2004 at 19:54

Saturday, Mar 13, 2004 at 19:54
Thanks KiwiAngler,
Being a pretty lazy type I'm inclined to mount them flat on my Rhino bars and know that they are always contributing a little. I accept that i will lose a bit of wattage caompared to the person who can construct and then align a system towards the sun.
FollowupID: 312021

Reply By: joc45 - Saturday, Mar 13, 2004 at 19:47

Saturday, Mar 13, 2004 at 19:47
I've been running solar panels on my roof for some years now. Sometimes flat, sometimes on a slight angle, never had a problem. I bought some 40mm x 40mm x 3mm aluminium angle extrusion, and made a frame to hold my panels together as one. I put up with about 20% less output by running them flat, but I like the idea that they never have to be set up - they are always there running. And when suitably bolted down, are less of a temptation to thieves.
In the early days, I thought the glass panel would need supporting underneath in the middle, so I packed some white polyfoam under it, but in practice, it isn't a problem, and I now run the panels only supported on the edges, as in a static installation.
Re stones, a glancing shot by flicked-up stone should just bounce off; a falling branch may be a problem. Just be careful when parking the thing. The glass is amazingly tough, tho.
There are solar panels which use a sheet steel backing and a clear plastic coating over the cells, which is a pretty tough combo, and even work after you've run over them. But several forumites had had a few negative things to say about these panels.
AnswerID: 50210

Follow Up By: Brad - Saturday, Mar 13, 2004 at 19:58

Saturday, Mar 13, 2004 at 19:58
Thanks joc45,
it sounds like you have a simple, solid set-up like I'm after.
Are the 'tough' ones you are talking about "uni-solar".
I'm thinking of getting the BP ones as they seem to consistently get good reports.
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Follow Up By: joc45 - Sunday, Mar 14, 2004 at 11:37

Sunday, Mar 14, 2004 at 11:37
Hi Brad,
Yes, a friend has the Unisolar, which in his case is a good idea, since he's accident-prone. Bent them once already, but they still keep working. For a given area, not as much output as the others, but they claim to give the same output when hot. My polycrystalline BPs definitely drop off their output when hot - chuck a bucket of water over them and the output goes up about 2A!! Mine are pretty old, tho - I'm using 3 x 43w BP units, all bolted together into the aluminium frame. The frame can mount either on pack bars, or to my roof rack. It can be hinged up to access stuff on the roof rack.
The main complaint about the Unisolar from users of this forum seems to be the problem of dust getting permanently ingrained in the plastic coating.
Get a good regulator - simple ones just cut off when they get to 14.2v. Better ones briefly take the battery up to 15v, then drop back to regulate at 14.2v. This allows the battery to gas, preventing stratification of the electrolyte, and equalises the charge in the cells. You'll get better battery life. There are really cool regulators which show amp-hours in and out, etc, but the price starts climbing.
FollowupID: 312086

Follow Up By: Brad - Sunday, Mar 14, 2004 at 20:05

Sunday, Mar 14, 2004 at 20:05
Thanks joc45,
Answers on this forum have helped.
I will prob go for a pair of Kyocera 35W as they will just fit in the drawers on my cruiser.
I will start by using them as free-standing - and depending on how they go I may subsequently "permanently" mount them on the roof-rack.
I will use them via a regulator to the battery in the camper which doesn't do much work (gas fridge in the camper), and other times connect them directly to the deep cycle in the cruiser which has to run the Engel.
Tell me if you think thats a plan !!
Thanks again - hopefully see you on the trail one day.
FollowupID: 312125

Follow Up By: joc45 - Monday, Mar 15, 2004 at 16:52

Monday, Mar 15, 2004 at 16:52
Sounds like the battery in the camper doesn't do too much work (lights?), so I'd be concentrating on keeping the aux battery in the vehicle charged, as that has to run the Engel.
One issue: The regulator has to go somewhere; if you want to be able to connect the panels to either the camper or the vehicle, then the regulator has to be part of your solar array assembly. With 70W of panels, I wouldn't be connecting them to the battery without a regulator - the panels put out about 23v max, and you could boil the battery.
An option is to mount the regulator in the vehicle, connected to the aux battery, then make up a cable to run from the vehicle's aux battery to your camper to top up its battery (you'd already have one to charge the camper battery from the vehicle when travelling). If you're only running flouros in the camper, you won't drain much, and the occasional topup would be fine. I'd be using about 8-10 sq mm cable plus Anderson plugs.
I note all the other readers' comments about not mounting the panels on the roof, and I understand their reasons. Must admit, the vehicle does get hot out in the sun, but I put up the sun screen, and drop the windows a bit, and it all works fine. Having read the reports of vehicles being smashed into to steal Engels, I reckon that a grand's worth of solar panels just lying on the ground would be a prime target for theft, hence my reason for bolting them on to the roof.
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Follow Up By: Brad - Monday, Mar 15, 2004 at 18:39

Monday, Mar 15, 2004 at 18:39
Thanks for the effort you've put into my solar education Gerry.
I'm a complete novice but you've given me food for thought.
FollowupID: 312215

Reply By: Peter 2 - Saturday, Mar 13, 2004 at 20:16

Saturday, Mar 13, 2004 at 20:16
The biggest problem with having them fixed on the roof is that you have the vehicle which presumably has the frig in it sitting out in the sun which causes the frig to run more due to the increased heat which in turn leads to increased power consumption negating the whole purpose of having the solar panels in the first place.
BTDT on a trip with a mate with the panels mounted in the pop up roof of his camper conversion. He had to park out in the sun to get the power, I had the truck in the shade with a 30 ft lead on the solar panel which sat out in the sun. Same size panels, vehicles, frigs etc, resulted in a whole day less frig operation due to flat batteries in his rig, plus he had to start it up twice a day to move it in and out of the sun from the campsite. Needless to say he removed the panels from the roof and made them into a hinged case for ease of carrying for the next trip.
If you are only connecting the panels in daylight hours you do not need a regulator as the panels will not overcharge a battery which has a frig running of it in a day.
Regulators usually cause a drop in voltage and current which is not needed or desirable when using small panels of up to 100 watts. But a regulator or at least a diode should be fitted on a permanently connected panel except if it is very small.
AnswerID: 50211

Follow Up By: Brad - Saturday, Mar 13, 2004 at 21:41

Saturday, Mar 13, 2004 at 21:41
i will give thought to these issues - at the moment i'm inclined to think I want a 'set and forget' solar panel that I know will contribute something when I'm forced to park in the sun (eg a day on the beach) and the Engel is working hard.
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Follow Up By: V8troopie - Sunday, Mar 14, 2004 at 02:55

Sunday, Mar 14, 2004 at 02:55
Peter 2 wrote:
If you are only connecting the panels in daylight hours you do not need a regulator as the panels will not overcharge a battery which has a frig running of it in a day.

Care to read that again Peter? :-)

BTW, the sun does not shine at night :-)

I would strongly recommend using a regulator with solar panels bigger than perhaps 20W. The voltage drop across the regulator is very small, nothing to worry about since the open circuit panel voltage is around 20V anyway. Most panels already have a reverse discharge diode fitted or supply one with the panel. The better diodes are the schottky types with a very small voltage drop. Fitting a regulator gives you piece of mind if the fridge battery also gets charged from the alternator (while you are driving) as the regulator will shut off or severely limit the panel output during this time.

I had a solar panel on the roof rack once and soon got tired having to park in the sun at every stop when there were lovely shady trees on offer.

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Follow Up By: Peter 2 - Sunday, Mar 14, 2004 at 18:31

Sunday, Mar 14, 2004 at 18:31
Yes that little sentence was a bit twisted ;-))
What I meant was that if you have a frig running off the battery and are only connecting the panels during the day there is no way you will overcharge the batteries unless the current rating of the panels exceeds the power consumption of the frig over a 5 hour period.
My two panels have a combined output of 44w so there is no need for either a blocking diode or regulator as I only plug them in during the day and then only if we are staying in one place for more than a couple of days and not driving the truck which rarely happens.
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Reply By: Peter 2 - Saturday, Mar 13, 2004 at 22:02

Saturday, Mar 13, 2004 at 22:02
yes the trouble is that the hotter it gets in the vehicle, the more the frig works, which in turn heats up the interior, it just keeps going, a vicious circle.
Another thing is that as you said having the panels horizontal is approx 20-30% less efficient depending on the orientation to the sun.
Also remember that at the typical latitude of Sydney/Brisbane you effectively only get 5 hours full sun per day in summer, less in winter and less the further south you go so when working out approximate daily output of the panels you multiply the wattage of the panel by five, less a percentage for incorrect elevation(angle) of the panel. At least if the panels can be kept in an approximate optimum angle (about 60 deg) for Sydney/Brisbane and also facing the sun (tracking) you can get that percentage back to some extent.
My additional reason for buying freestanding panels years ago was that if by chance we were stuck with a flat battery in an isolated spot that I could put the panels out in the sun for a day or so and put enough back in to start the truck. In fact I've done this with the brother in laws truck when it was parked in such a position that it couldn't be jump started, but after a few hours with the solar panel hooked up it started. Yes I know we could have swapped batteries but it was too nice on the beach to think about hard work!
AnswerID: 50239

Follow Up By: Brad - Saturday, Mar 13, 2004 at 22:42

Saturday, Mar 13, 2004 at 22:42
thanks once more,
So tell me what sort of panels do you have, did you make a stand yourself (or can you buy one for the situation you describe), and finally I guess you have a regulator with your set-up ?
FollowupID: 312058

Follow Up By: Peter 2 - Sunday, Mar 14, 2004 at 18:21

Sunday, Mar 14, 2004 at 18:21
I have two 22w panels made by solar cells Australia, they are no longer in business AFAIK. I've had the panels for about 15 or 16 years now and they were built by Quirks at botany to keep up with an Autofridge which they do admirably.
The panels are very similar to a BP panel with an aluminium frame around the edge which has hinges along one edge and a catch on the other allowing them to shut with the actual solar panels facing each other, like a suitcase. I do not run a regulator for the reasons I mentioned earlier(voltage drop, current drop, panels are not permanently connected).
I never leave the panels out if we are not in camp, usually we would be driving anyway so the panels are packed away, avoiding the theft problem. In fact unless we are staying in one spot for more than three days I don't bother getting them out and on most outback/long trips I only carry them to have a method of charging the batteries if the alternator should cark it. The panels would provide enough juice to keep the battery going in a non EFI diesel vehicle.
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Follow Up By: Brad - Sunday, Mar 14, 2004 at 19:42

Sunday, Mar 14, 2004 at 19:42
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Reply By: Member - Raymond - Sunday, Mar 14, 2004 at 09:41

Sunday, Mar 14, 2004 at 09:41
Hi Brad
Went through this problem a few years ago, I ended up with two Unisolar panels, I 32 watts 1 64 watts. The fact they are not glass makes them much harder to damage. I have them free standing so as to keep the camper in the shade and have the panels in the sun. I use a 20 watt solar regulator from jaycar STOCK-CODE: MP3126. Both panels in the bright sun put out 23 volts each and I was surprised how quickly the battery with out the regulator attached had more than 15 volts going into it. The night had been cool so the fridge did not draw much and there was full sun the next morning.
AnswerID: 50271

Follow Up By: Brad - Sunday, Mar 14, 2004 at 10:50

Sunday, Mar 14, 2004 at 10:50
Thanks Raymond,
I'm starting to sense an overwhelming consensus to have free-standing panels :-)
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Reply By: brianm - Sunday, Mar 14, 2004 at 12:26

Sunday, Mar 14, 2004 at 12:26
I think I do what you want to know. I had my two panels in a portable frame that
I use to move around to catch the sun, The wind would blow them over,risk of getting stolen. Yes thieves opperate in the bush as well as citys.I have herd of panels getting stolen 100skm
from anywhere when you think you are alone.
I now have my two 75w panels in a frame lying flat on the roof (I know I am not
getting full benifit) But it does what i want, I run two 40lt engels one as a freezer.
I have a sunsaver regulator and two 6volt deep cycle batts . I turn the freezer back to no1 setting when the sun starts going down. I have been out for 4weeks and
never had a shortage of power. Hope this helps you.


PS. i only go bush in the cooler months.
AnswerID: 50287

Follow Up By: Brad - Sunday, Mar 14, 2004 at 19:30

Sunday, Mar 14, 2004 at 19:30
Thanks brianm,
I've got a bit to think about.
FollowupID: 312118

Reply By: Member - John- Sunday, Mar 14, 2004 at 22:15

Sunday, Mar 14, 2004 at 22:15
I currently use 2x 65W panels on the end of a cable out in the sun when I am base camping. Works pretty well and the truck stays in the shade.

I'm thinking of mounting one on the roof permanently and still keeping on to set up on a long lead. Give the most flexibility.

AnswerID: 50335

Follow Up By: Brad - Monday, Mar 15, 2004 at 07:43

Monday, Mar 15, 2004 at 07:43
FollowupID: 312158

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