Solar panel on roof

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.
Regards,
brad.

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.
Regards,
Brad.

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.

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.
Regards,
Brad.

Brad,
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.
Gerry

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.
Regards,
Brad

Thanks,
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.
regards
brad

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.

Klaus

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.

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 ?
Regards,
Brad

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.

Thanks.

Thanks Raymond,
I'm starting to sense an overwhelming consensus to have free-standing panels :-)
Regards,
Brad.

Thanks brianm,
I've got a bit to think about.
Regards,
Brad

Thanks