Moveable Solar Panel

CA

camperD

Senior Member
Joined
Jul 16, 2011
Messages
102
Location
Marietta, OH
I just got a 100 watt solar panel kit (with solar panel, 30 amp charge controller, mounting clips, and some 12ga wiring) so we can go camping without plugging into shore power or running a generator. I'm thinking about not using the roof mounting clips and just have the panel moveable. That way we can have the trailer in the shade and the panel in the sun. Anyone have any experience with how much cable I can use and what angle (if any) up from horizontal I need to allow for?
 
I think you could easily use up to 100 ft of cable with that panel. You will NOT get 100 Watts, even on a bright sunny day and the panel optimally placed.

I'm going to guess here and say that you will see a charging current of between 4-5 Amps, with the panel pointed right at the sun. Your 12 ga wire should have no trouble passing that current with minimal loss.

You are somewhere around 40 degrees north, if I'm not mistaken. But, the angle for your panel is really dependent on the time of the year and where you are camping. If you can, mount it with adjustable legs that allow you to tilt the panel so that it is close to perpendicular to the sun's rays. You can judge perpendicular by looking at the shadow behind the panel when it's in use.

- Jack
 
I carry one and move it around where I need to. Find the thickest wire you can. I've read where some folks use welding cable. I've got a little collapsible dolly that I set it on and prop it at whatever angle I need depending on time of day. 100 watts is a pretty hefty panel in terms of output.
 
hilltool said:
I carry one and move it around where I need to. Find the thickest wire you can. I've read where some folks use welding cable. I've got a little collapsible dolly that I set it on and prop it at whatever angle I need depending on time of day. 100 watts is a pretty hefty panel in terms of output.
Click to expand...

But, even though it's rated at 100 Watts, solar panels are not very efficient. I used to have a 60 Watt panel (still do), and I found I could not get much over 2 Amps output under perfect conditions. At 15 volts (an optimistic charging voltage) that's only 30 Watts. That's what led me to say the OP would get no more than 4-5 Amps.

Remember too, 100 Watts is the draw of an ordinary incandescent light bulb. You don't need welding cable for one of those.

- Jack
 
JackandJanet said:
But, even though it's rated at 100 Watts, solar panels are not very efficient. I used to have a 60 Watt panel (still do), and I found I could not get much over 2 Amps output under perfect conditions. At 15 volts (an optimistic charging voltage) that's only 30 Watts. That's what led me to say the OP would get no more than 4-5 Amps.

Remember too, 100 Watts is the draw of an ordinary incandescent light bulb. You don't need welding cable for one of those.

- Jack
Click to expand...

The wire gauge has more to do with voltage drop than current handling in this instance. The longer the wire the greater the voltage drop.
 
RichR said:
The wire gauge has more to do with voltage drop than current handling in this instance. The longer the wire the greater the voltage drop.
Click to expand...

Correct, but the resistance of 12-gauge wire is fairly minimal. Ohm's law (V = IR) determines the voltage drop and if you measured the resistance of that wire, you'd find it was negligible.

You could certainly check the drop though. Connect the solar panel to the battery through the charge controller and then place the voltmeter probes at each end of the wire. You'll be reading the loss.

- Jack
 
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12 gauge would be more in line. If heavier wire would be close in cost to 12 gauge I would spring for it or if a long length is desired. I think a 12 gauge extension cord with modified ends would make a good feed line.
 
Renogy (the solar panel brand) had a website for calculating the cable thickness vs. length. The design max voltage drop was 5% between the panel and the charge controller with their specific panel max operating voltage (17.8) and amps (5.6). I played around with the calculator and found that 12awg would fit within their design limit up to about 47 ft. Above that I would need 10awg.
The kit only had two 20' 12awg cables. Since I had to buy longer cables anyway, I went with a 100' 10awg cable with MC4 connectors on both ends. I cut it in half and have two 50' cables with MC4 connectors at the panel end and put Anderson quick connects on the other end. I'll use some of the 12awg cable for hooking up the controller.
I found an easy DIY adjustable tilt frame on YouTube made of slotted angle. I got two 6' pcs. of 1-1/4" 16ga slotted angle, and the resulting frame covers all the tilt angles I'll need.
So for under $300 I'll have a solar system that should keep up with our electrical power usage while boondocking.
 
JackandJanet said:
But, even though it's rated at 100 Watts, solar panels are not very efficient...
Click to expand...

Good panels are about 20% efficient. That means they convert about 20% of the energy striking them into electricity.

Concerning how much power you will realize vs the panel's rating has more to do with how the panel was rated in the first place.

An example - a panel may be rated at 60W @ 20V (20V x 3 amps = 60W). As soon as you connect a battery to it the input voltage drops down to the battery voltage, maybe 13V. So now it is 13V x 3 amps. It can now only make a max of 39W even though it truly is a 60W panel.
 
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