Adding more solar panels to AF 30U

We have a 2010 Arctic Fox 30U that comes with one 150W solar panel mounted on the LR of the roof.  There is room on the front of the trailer (both sides) and the RR of the roof for more panels.  I need at least one more panel, but could probably afford to add 3 more.  We boondock most of the time, and I can get additional panels for about $250 each.  I have 6 GC-2's in this unit.

Question:  How do I wire the additional panels? 

Some have suggested plastic conduit outside on the roof between them. Sounds a bit tacky to me.  However, trying to retrofit heavy wiring in the ceiling to 2 or 3 more panels does not sound like fun either.  Can't see much in there from the fantastic fan vent holes other than wads of fiberglass.  Does one try to pull wires with a snake though that, or bore right through into a cabinet top somewhere, and pull through there?  I would probably have to do this for EACH additional panel, as I don't have enough room anywhere on the roof to butt 2 or more panels together.

I know that I will have to replace the solar controller with something larger, and quite possibly replace the existing wiring, as it may be way too light.
More questions to come after I hear from you. 

​Thanks.

Frank.

My general suggestion would be put the panels as close together as possible with minimal to no shading, and connect them in series, and use a MPPT controller, which will allow you to use smaller wire between the panels and down to the controller.  With ~660 amp hours of batteries, I would think a minimum of 600 watts of solar would be required, and 800 watts would be preferable to optimize your system.

Thank you for that very valuable bit of information. I was not even aware of what MPPT controllers are, and what they can do. This sounds like exactly what I need for my system, and it looks like three additional 150 watt panels will be what I'm looking for.

After going up on the roof of the trailer again today, I think I see how I can put four panels together edge to edge. I just need to remove the AM radio antenna, which I don't use anyway.

One more question. Does it matter if the panels are somewhat mismatched? They would be the same number of cells (4x9), and the same wattage, but not from the same manufacturer necessarily.

Frank .

I am not that well versed in mismatched panels, but I believe that if the voltages are close, they will work fine, however, I dont believe using a nominal 12 volt panels with nominal 24 volt panels will work well.  Hopefully, someone on here has more knowledge on this issue.

I may have an answer on that already in another thread. They would be comparably rated.

I'm checking out a local supplier now. They make kits, so should be able to steer me in the right direction.

Thanks again.

Frank.

Thanks.

Another suggestion... You might want to consider a rooftop junction-box. Mount it on the roof, somewhere close to where it will be relatively easy to run wires from it to wherever you're going to mount your controller. Run the wires from all the panels along the roof to the junction-box, and then run two larger gauge wires from the junction-box to the controller. Then, of course, two more large gauge wires from the controller to the battery-bank, through a fuse.

Paul's suggestion to connect all the panels in series will work (if you've got an MPPT controller) and it will enable you to run thinner gauge wire, but it may not be the most efficient method of wiring your panels together.

Our system is wired exactly as I described - with a junction-box - but our six panels are wired in parallel and series. Each two panels are wired in series to double their output voltage (amps stay the same) then all three sets of two panels are wired in parallel to tripple their amps. They're wired like that, because we have an Outback MPPT controller, and on 12 volt systems, the controller is most efficient at converting volts to amps when its input voltage is between 36 and 42 volts. If you combine the output voltage of four 150 watt panels, it'll be closer to 80 volts, which means you'll lose some efficiency - not a lot, but when it comes to solar, I'll take all I can get.

That's the beauty of a junction box. It enables you to connect all the panels' wires at one location, and you can always add additional panels. Depending on your controller, you can also experiment with which type of wiring works best - parallel or series. I always recommend thicker gauge wire for RV solar installations. Go as thick as you can afford and can work with. Wiring that's too thin is one of the most common RV solar-install mistakes.

Kev

Kevin:

So, I assume your panels are nominal 17 volts, or thereabouts?  100 watt panels?  In any case, there must not be a lot of room to walk around on that roof!  ;D

Frank.

Kevin,

As to the junction box, do you run wires along the surface of the roof to that junction? Don't they flap around in the wind when traveling?

One thing to keep in mind when wiring panels in series is that any shadow on any panel will have a great effect on the output of the whole system. In parallel, only the panel with the shadow will be affected.

kbdgoat:


Ah.  THAT is good to know, and could make a major difference in how I eventually wire this thing.


Thank you for the input!


Frank.

Panels wired in series have an output voltage equal to the sum of the panels, but the current from the string will be restricted to the lowest performing panel.  Put a 5 amp, a 6 amp and an 8 amp panel in series and you'll only get 5 amps from the string.  Let one panel get partially shaded so it's current drops lower than that and the current from the entire string will drop to that value.

Panels wired in parallel are just the opposite - the currents contributed by each panel will add to the total but the working voltage will be limited to the lowest voltage panel in the string.

Solar cells produce about 0.5 volts each, so as long as each panel has the same number of cells you can combine them in parallel without losing capacity.  The current ratings don't matter, they'll simply add together.

But if you put a 32 cell panel with a nominal 15 volt output in parallel with a 36 cell panel with an 18 volt output the voltage from the pair will equal the voltage of the lowest voltage panel.  You'll lose 20% of the higher voltage panel's power.

Since Power = Voltage x Current, if you put panels of wildly different voltages in panel, you'll lose capacity as the higher voltage panels are pulled down to what is produced by the lowest rated panel.  Put a 12 volt panel in parallel with a 24 volt panel and the 24 volt panel will lose half of it's rated capacity.

Wire caused voltage loss is important to keep at a minimum, but it's most critical between the controller and the batteries.  Mount the controller as close to the batteries as you comfortably can to get the best charging current.  If the controller is too far away from the batteries you'll lose peak charging current, just the same as if a trailer's converter is located a distance from the batteries.

Frank, each of our panels puts out between 21 and 22 volts in direct sunlight. And yes, the wires from the panels to the junction-box run right along the roof. That's the most common method of running the wires on RVs with multiple panels. Our wires are secured to the roof about every two feet with wire straps that have 3M backing - they stick to the roof - there's no flapping around at all. I'd also recommend using UV protected wire on the roof. It's more expensive, but you'll only have to do it once.

Kdbgoat is correct about panels that are wired in series - if one of them is shaded, the output of the panels wired in series with it will also be affected, and it doesn't take much shading to reduce their output to almost nothing. However, that shading will have no impact whatsoever on the output of other panels that are not wired in series with the shaded panel. They'll still produce full power to the junction-box.

Kev

A question about your system, Kevin.  How many volts do you see going into your controller?

Thanks!

Lou, Kevin and others,


Well, you've all given me a lot to think about.  Now I'll have to decide what set of compromises works best for me.


Kevin:  I thank you for that answer on how to wire the solar panels.  Though that answer is perhaps simple to you, it is the answer that I have been looking for.  I found it strange that wiring would be just laid on the roof, but if that is what is done, then great!  Makes my job much simpler.  I thought I was going to have to put a hole in the roof under each panel, then try to fish wires through the fiberglass in the roof 'cavity'.  What you mention is much simpler, and, as you state, allows one to use a junction box, and mix and match according to need.


Even this year, I just added a 100w solar external panel that I had, right across the battery bank to augment the output from the roof mounted 150w panel. When controller says batteries are charged, I unplug the other one. Even with this totally non technical setup, we have kept our 6 GC-2 batteries up for over a week, using TV, toaster, two laptops, and sometimes the microwave. So we don't need a lot more.


If/when I add more roof panels, I will likely have to rewire and/or reposition the solar controller, as it is presently at the BACK of the trailer, the converter is under the kitchen counter, and the batteries, of course, are toward the front.  That is now going to be the hard part.  It will also have to be just plain replaced with an MPPT type.


Thanks again, all, for your most valuable input.


Frank.

Paul, in Picture 1, the VOM's display is indicating 41.6 volts. That's the voltage from the output of two panels wired in series. There are three sets of two panels on the roof and each set has almost exactly the same output. That's the voltage going to the controller. The picture was taken in January of this year at about 2:00 PM for someone else who wanted to know our panels' output. Notice that the panels are fairly dirty. Had I cleaned them, and had the picture been taken at noon, the voltage would be closer to 42 or 43 volts.

Frank, Pictures 2 and 3 show the wiring on the roof. It's a very typical way of wiring RV solar panels. We used 8 gauge UV protected wire and honestly, it wasn't very easy to work with - pretty stiff - especially when going into the junction-box, but there's no measurable voltage loss and it should last forever. In picture 2, you can see how the (+) and (-) wires from each panel go to the (+) and (-) terminal blocks. That was how I initially wired the panels - so each panel was independent of the others. if one got shaded, it wouldn't affect the others. However, that did not produce the optimal voltage to the controller (per Outback), so at their suggestion I rewired them at the junction-box so every two panels went to the terminal block.

I'm not suggesting that this is the only way to do it, but so far, it has yielded the best results. If you look closely at the top of the open junction-box, you'll see the two larger gauge wires that go the controller. Those are 4 gauge wires and they're about 15 feet long. Once again, there's essentially no measurable voltage loss, because of the heavy gauge wire.

If you're going to install multiple panels, I'd definitely consider a junction-box vs. drilling holes for each panel and routing their individual wires to the controller.

Kev

Looks like a very tidy installation.  Thanks for the pics.  One more question; what is the most watts you have seen your panels produce?

Thanks, again

Paul, our Trimetric battery-monitor and the Outback controller are programmed to display amps, because I'm not smart enough to do the conversion to watts.  This past summer I ran the batteries down to 80%, so the controller would show max output under the following conditions; clean panels and direct sunlight during the summer in San Diego - in other words - best case scenario. Under those conditions, the Outback indicated that it was charging the batteries at a little over 46 amps per hour. Plenty of power to not have to run the genset (unless we need the air conditioner)

In the winter, we usually camp in the So Cal and Arizona deserts where shading usually isn't a problem and where there's usually plenty of sunshine (about six hours each day this time of year.) Under normal conditions, with winter's low solar angle, the Trimetric indicates a charge rate of about 30 to 38 amps per hour during the solar charging window. With our power-hungry motorhome, that's just enough amps to not have to run the generator at all - even with a residential refrigerator and a 2800 watt PSW inverter running non-stop.

Kev

To follow up on this topic with some information... We just got back from camping at a place called KOFA in the Arizona desert. While there, I took a couple of pictures of the Trimetric battery monitor to show how many amps our residential refrigerator draws when the compressor is on vs. off. In picture 1, the Trimetric is indicating that the solar panels are putting just under 30 amps per hour into the battery-bank - that's with the fridge's compressor on, the 2800 watt inverter on (obviously) and while a couple of cell phones and a laptop are charging (plus a few phantom load amps). Picture two was taken about 30 minutes later with all the same loads, but after the fridge's compressor had kicked off.

Our fridge is fairly big (22 CF) so it's at the high end of the power consumption chart. I'm sure smaller res-fridges would draw noticeably less power - especially if they didn't have ice-makers. A smaller fridge would also require a smaller inverter, so that combination would draw even less power. No big deal when hooked up to a pole, but a significant factor when boondocking.

Kev

Kevin:


Now I see why you have a big solar setup.  A conventional compressor refrigerator swallows a whole lotta power!  Gotta be tough boondocking with that.


Thank you for the pictures as well.  I understand better now about the junction box, and the wiring on the surface of the roof.  Looks like you have room for yet more panels, should you decide to.


Just curious -- why not an RV style fridge?  They take next to no power when running on propane.  Even a pair of them, if additional space is needed.


Frank.

Frank B said:

Just curious -- why not an RV style fridge?  They take next to no power when running on propane.  Even a pair of them, if additional space is needed.


Frank.

Click to expand...

An LP fridge wasn't even an option when our coach was new in 2011. If I remember correctly, the last year you could get an LP fridge in a Tour was 2010. Even so, we prefer our residential fridge over our two previous LP fridges. It's got more capacity, more even cooling, faster cooling, no flame etc. It definitely requires more attention to power management when boondocking, but it's not an insurmountable problem. If I were in the market for a new RV fridge today, I'd stick with a RR, but I doubt I'd buy one that's as big as ours.

Kev