Solar Output in Shade?

ktmrfs wrote:

westend wrote:
I'd suggest to mount one on the roof and carry one as a portable. You'll have the best solution possible. The portable one can be smallish to ease setup and tear down or use multiples. Remember, you'll be driving on the road and harvesting, along with the excellent battery maintenance solar does while in storage.

that is certainly a good option, and the two panels can still be connected to one charge controller.

And, if you do much driving vs. camping, the days drive can pick up lots of AH, combined with what you can get from the TV charge current can be a big boost.

I have thought of the two different options of solar for my needs.(fixed and portable). Doing both seems the best. Is there an easy way to have things wired so the portable panel can be quickly hooked up using both panels or not used at all leaving the roof panel on its own working?

ktmrfs wrote:
Now, with panels in series you minimize resistive loss in the cable, but risk low output if one or more panel gets shaded. output current will be limited to lowest panel output.

Unless the panels have bypass diodes then series can easily outperform parallel.

westend wrote:
I'd suggest to mount one on the roof and carry one as a portable. You'll have the best solution possible. The portable one can be smallish to ease setup and tear down or use multiples. Remember, you'll be driving on the road and harvesting, along with the excellent battery maintenance solar does while in storage.

that is certainly a good option, and the two panels can still be connected to one charge controller.

And, if you do much driving vs. camping, the days drive can pick up lots of AH, combined with what you can get from the TV charge current can be a big boost.

I'd suggest to mount one on the roof and carry one as a portable. You'll have the best solution possible. The portable one can be smallish to ease setup and tear down or use multiples. Remember, you'll be driving on the road and harvesting, along with the excellent battery maintenance solar does while in storage.

BFL13 wrote:
If you don't want one big 24v panel just use two smaller 12v panels in series. The only thing is make sure the solar controller has enough Voc input limit for all the panels in series (add their Vocs)

yup, that's what I do. I have 3 160 watt portable 12V panels in series running up to 150 ft in one favorite camping location with a MPPT controller in the pass through. If I know I have full sun I can connect them as six 12V panels in series which my controller can take since it has a 150V max input.

and a 160W portable folding panel is about as big as I want to lug around.

Now, with panels in series you minimize resistive loss in the cable, but risk low output if one or more panel gets shaded. output current will be limited to lowest panel output.

If I risk shade during the day I run the panel in parallel, but increase resistive loss during high output but not as affected by shade. Pick your poison.

BTW my cable is sections of 30A power cord connected via anderson connectors. And parallel the ground with one of the other wires. So the cable is basically one 10ga wire and one 8 ga wire. Resistance of 100ft is about .156 ohms

For a full output panel with a 30A controller, I'm limited to about 25A with panels in series which is noticeable power efficiency loss about 90 watts in the cable. or about a 3.5v drop in the cable

in series current is about 8 A so power loss is down to about 9 watts or about 1.2 volt drop.

now with a PWM controller you stuck with running panels in parallel, but unless the resistive loss gets voltage at the controller down below about 14V you don't affect battery current.

again its all a tradeoff

If you don't want one big 24v panel just use two smaller 12v panels in series. The only thing is make sure the solar controller has enough Voc input limit for all the panels in series (add their Vocs)

95 degree day...

Park in sun to harvest 300 watts solar...

Run generator to cool 110 degree rig...

Move to shade...

Use generator occasionally to recharge battery...

Your mileage will vary...

OK, now that I've digested all this......

Background - I have 2 G29 12V flooded batteries. Charging is via an IOTA 55A deck-mounted converter w/ charge control when on generator. It's mounted in the front pass-through and run to the batteries with 4ga welding cable.

Much as I'd like to put 250 watts of solar on the roof I don't believe it'll work in the sites we like given the output drop-off in shade. Too bad - I have enough real estate on the front of the TT roof for a panel and could run the cable down through roof, into the front bedroom closet and then into the pass-through.

So - To get an unobstructed south-facing location I'd need app 100' of cable on a portable solar panel. Given the distance involved I'm thinking of going with a 24V system with a MPPT controller mounted next to the IOTA in the pass-through. I'd have to cable-lock the panel to a tree as I'm afraid of it growing legs if we're gone for the day. The problem is finding one or 2 24V panels small enough to be reasonably portable. DS works for a solar installer and they buy 24V 260W panels by the truckload but they're a bit large to be "portable."

I'm in the 100W portable group, since we're in the northeast (where we have trees, not so much cactus...). Used 50 feet of low voltage landscape lighting cable to make an extension cord this summer. No noticeable drop with the 50', end result is access to much better sun, hence much better output! ST

The following graphs are for shade output. These are serial panels with bypass diodes.

Casa Grande, AZ 3/5/15, Begin Civil Twilight 6:25 AM, Sunrise 6:50 AM
Leafy shade

Oceanside, CA, 12/26/14, Begin Civil Twilight 6:17 AM, Sunrise 6:45 AM, No picture but large heavy shade trees were several blocks away.
Far away trees