Dual Solar Panels, in Series, Tilt-able

[MarkBC]

MODEL TWICE, CUT ONCE!

I expect to get this solar panel installation project done before I leave on my next trip October 8...believe it or not.

• The project started as "mount one 120-watt panel to the roof of my camper using the "z-brackets" from the panel vendor" (SolarBlvd.com).
• Then, when looking at the roof of my camper, it came to me that two such panels would fit up there if oriented so that their aspect ratio-orientation was the same as the camper roof (i.e., the short ends at the front and back). And more panels = more power = good.
• Then I decided that I didn't like how high the z-brackets hold the panels off the roof, so I came up with a different mounting plan using a supply of aluminum angle stock I bought some time ago (1/8" "architectural").
• Then, when I hit a snag with my mounting plan, it came to me that it wouldn't be hard to make the whole thing tiltable to improve the incident angle of the sunlight -- make it closer to "normal" (aka "perpendicular"), and thus improve the solar gain.
• I spent quite a bit of time visualizing and working out the details of a tiltable mounting system in my head, which worked pretty well, but eventually I decided I needed to get something down "on paper" -- virtual paper -- to help with planning.
• This morning I re-discovered Google (now "Trimble") SketchUp 8 -- 3D modeling software, and found it easy to learn...and cool, too.

Not shown are similar mounting brackets on the two hidden sides of the panel assembly. And, of course, there will be other screws and bolts required -- not drawn.
In the lifted position the bolts would actually stay with the panel-attached brackets, not down on the camper-roof brackets as shown in the drawings...modeling error.
The front and rear brackets would be positioned to be aligned with the frame of the camper roof, while the side brackets will have to be attached to cross-members that will be attached to the roof frame.

• I haven't worked out what will hold/prop the panels in the tilted-up position...probably more aluminum angle...maybe a pile of pine cones.
• Tilting will be possible front or back or left or right.
• Tilting will only be employed when camped -- not while driving.
• The panels are wired in series, producing a nominal 24 volts (actually more like 35 volts), and brought down to the proper voltage with my MPPT controller. Nice, since it means I get more power without using heavier wire between the panels and the controller.

CRAZY? Maybe...but as long as the panels aren't ripped from the roof while I'm driving I'll consider it a success.

As I take this from virtual to actual in the next couple/few days I'll take pictures, of course. But I think the computer-generated images are pretty cool...

 

[pods8]

If you can easily swap the connectors around it'd be interesting to see the efficiency differences in running the panels in series verse parallel. You noted the lower required wire gauge which is a + to parallel. I'm curious if the controller is more efficient with getting something closer to 12V in or if it doesn't really matter. The big perk will be for lower light situations where the panels output voltage might fall too low individually but may double up to get you enough to still he usable. Keep us posted!

 

[ski3pin]

Mr. BC, I'm intrigued with your design. It is fun thinking and planning these things out, isn't it? Initial questions, what do the two panels weigh in tandem (ease of tilting up on the roof?), how will you be routing and securing wiring for the multiple tilting options (seems like right to the center would be optimal), and how will you be getting up to the roof for deployment? I figure these are all things you've been thinking about.

 

[MarkBC]

Good questions, Mr, 3pin...yes, I've considered all those, though I can't say I've answered/resolved them completely.

Bottom-line/Worst-case: The design will still function fine as a flat-mounted setup if the tilting aspect is problematic.

Together the panels weigh 50 lbs, so it won't be easy to Lift-n-Tilt™ but I think it'll be do-able.
I may have to bring along a lightweight ladder.
I think that if I have a ladder then lifting won't be harder than lifting my camper roof (pre-roof-lifting-thingys).
The wiring (panels in series as I've said) will be a combination of the MC4 connectors that came on the panel cables and maybe my new Powerpole connectors (then protected by shrink-tubing) and connected to the weatherproof outlet/plug that came pre-installed on the roof of my camper, which is ~centered front-back and left of center. All of the wires and the plug will be hidden/protected underneath the panels when the panels are down.

The reason for having two panels and making them more effective -- tiltable, and so, pointable at the sun -- is for times when I don't travel somewhere every couple of days, times when my truck's alternator won't be helping to re-supply the power that my 4.5 ft3 DC-compressor fridge, lights, laptop, etc. are sucking from the batteries. Maybe for use when I'm parked in that huge BLM parking lot outside Quartzsite, AZ for weeks at a time...?

.
So having to deal with a few minutes of set-up difficulty is worth it if it's something that provides days of benefit.
How much benefit? It depends on the latitude of my campspot, and the higher the latitude the more the benefit, relative to flat-mounted. A flat-mounted/horizontal panel receives a fraction of the available solar input in proportion to the cosine of the latitude. So, at a latitude of 45° (just north of Bend, say) at noon, a flat-mounted panel receives 71% [cos(45°) = 0.71] of the power that a south-facing panel tilted at 45° receives. In the winter the effect is greater the higher the latitude. So, this may come in especially handy if I decide to winter in northern Alberta.

Originally, I was going to compensate for this latitude-loss by just adding the second panel, and I figured that if I wanted to make it tiltable (a desire I've had even before I bought my first panel two years ago -- which is why that one is still free-standing) I'd add that ability some time in the future. But when I came up with this very simple solution I figured, "Why not?". Even though all I have is a saber saw and a hand drill (powered) and limited experience, I'm sure I can pull off this simple setup.

At future WTW Rallies I'll have an inverter set up so that people can charge their batteries off my solar-powered system.

--------------------------------------------
And bottom, bottom-line: It was a great opportunity to learn to use SketchUp to draw my vision -- amazingly powerful, for FREE software!

 

[Gormley Green]

CRAZY? Maybe...but as long as the panels aren't ripped from the roof while I'm driving I'll consider it a success.

Well there's a fine engineering goal! Looks like a very cool design, I look forward to seeing it one day.

*EDIT - and charging some stuff

 

[MarkBC]

Well there's a fine engineering goal! Looks like a very cool design, I look forward to seeing it one day.

*EDIT - and charging some stuff

The real challenge in pulling off this project is that the fabrication division of MarkBC, Inc. isn't nearly as strong as the engineering/design division.

 

[craig333]

Wow, if all my projects turned out as originally envisioned, well we can all dream right?

I'm happy if they turn out "acceptable". If I didn't use duct tape and bailing wire I did good

 

[MarkBC]

Wow, if all my projects turned out as originally envisioned, well we can all dream right?

I'm happy if they turn out "acceptable". If I didn't use duct tape and bailing wire I did good

And "acceptable" I think I've achieved.

The real-world version is very close to the design, in terms of layout and hardware...
EXCEPT: at this point I didn't include hardware that permits side to side tilting -- just to the front and to the back...and in practice I don't plan to try to tilt it on this first trip. There were a couple of details about the brackets that need trimming/refining before I try to actually tilt it. I still like the tilting concept so, at this point, I still plan to add side-tilt brackets...in the future.

I think that it won't fly off the roof as I drive.

• The aluminum is 1/8"-thick architectural angle stock.
• The down-brackets -- the 4 parts that anchor the assembly to the camper roof (and which provide/support the potential tilt-pivot points) -- are each secured to the roof frame with two #8 x 3/4" stainless self-starting screws, sealed with Geocel "Proflex RV" sealant.
• All of the parts are fastened together with either 1/4" or 5/16" SS bolts and mostly using locking nuts.
• I attached strips of adhesive-backed 3/8"-thick closed-cell foam to the underside the panel-edges/frame-edges...kinda like weather-stripping (which is what it actually is) or maybe as a cushion against rubbing against the paint...something like that.
• Panels wired in series and plugged into the socket OEM-installed on the roof, the mess hidden underneath the panels.

Credits:

• Thanks to pods8 for the suggestion to use Powerpole connectors (part of the in-camper wiring to the charge controller and meter).
  
• Thanks to non-WTW-friend Don G. for cutting my aluminum angle stock into the required pieces with his chop saw.
  
• Thanks to Craggyman for help lifting the two-panel assembly to/from the roof.
  
• Thanks to Craggyman for the suggestion to use locking nuts.
  
• And thanks to Gormley Green for losing a PV-panel-anchoring nut which inspired me to follow Craggyman's locking-nut advice.
  

 

[MarkBC]

By the way, it's not too hard to lift the roof with the 50+ pounds of solar panels & hardware, thanks to the roof-lifter assist struts.

 

[Gormley Green]

Looks very pro. Any pics of it tilting fore and aft? Curious how much tilt you built in. Unless you meant you actually cannot tilt it yet.

 

[MarkBC]

Looks very pro. Any pics of it tilting fore and aft?

Thanks, GG, and no, I haven't tried to tilt it yet so no photos of that. I was figuring to tilt it up to 45°, the wiring underneath has enough slack for that (at a minimum).
The truth is that I need to trim corners off the brackets, as shown in the design drawing above, in order to keep them from scraping on the roof, etc...but I threw in the towel on that for now in the interest of getting something usable done before my trip...and I didn't yet have a prop-it-up solution either...couple other details. One more day and I probably could have it in "ultimate" form, but I can do that when I return home in a couple weeks.

Even in its sub-optimum flat-mounted state, 240 watts of (theoretical) solar capacity is probably good enough...as long as there's sun.

 

[Gormley Green]

For sure. My 120 flat mounted is enough for my needs in all but the worst locations/weather. Keep us posted.

 

[MarkBC]

For sure. My 120 flat mounted is enough for my needs in all but the worst locations/weather. Keep us posted.

If you can find enough sun in B.C., then I should have no trouble at all in my usual Great Basin haunts.

 

[Gormley Green]

If you can find enough sun in B.C., then I should have no trouble at all in my usual Great Basin haunts.

Getting off topic but we have had almost all sunshine since July 1! Absolutely incredible run of blue skies. I have a feeling the solar is about to stop working for a long time though

 

[highz]

Looks really nice, Mark.

 

[MarkBC]

Yay! Got the camper re-mounted on the truck without knocking it over!

Believe it or not, in the 6½ years I've had the camper this is only the second time I've had it off the truck

so it's not something I've got down pat.

All set to head off south!

With the price of gasoline in California at an all-time high, I'm gonna see if I can get my truck converted to electric and run it off the solar panels on the roof...I'll probably have to put the panels in tilt-mode to get enough power.

 

[CraggyMan]

Just my usual paranoia of hand tightened mechanical connections but I would definitely be rechecking the 4 attachment points quite frequently once you start going off road. Hate to see those nice Chinese panels go sailing. My $.02 and thanks again for the website updates.
Cheers - Craggy

 

[MarkBC]

An example of my MPPT charge controller doing it's thing on the high-voltage output of my two panels in series.
The upper meter shows the voltage and current upstream of the controller and the lower meter shows the stats downstream of the controller. (the numbers in the lower left cycle through various cumulative stats)

As you can see from the watt readings, about 7% of the power is lost in conversion.
If I had wired my panels in parallel, each panel would have been trying to put out half the parallel voltage (so, about 16.1v), but since the battery only needed 13.9v at that time, then the difference would have been lost, wasted (14% loss), rather than being transformed to more current as the MPPT controller does.

Is this -- 7% loss vs 14% loss -- a big deal? No...but when my battery isn't nearly full, when the charging voltage is lower, then the difference can be significantly greater, more MPPT benefit.

Now, I'm not trying to convince anyone of the value of MPPT...but I'm glad that I got one...YMMV.

 

[MarkBC]

In this morning's photo the meters are loose on the camper couch, and so is the charge controller because I hadn't finished with the inside mounting part of my project (even though I'm several days into a trip and am currently camped at 9700' in the eastern Sierra Nevada ).
This afternoon I finished...more or less, screwed the controller to the camper wall and affixed the meters to the front of the controller with Velcro.

Not real pretty...but functional.

At some point, when I'm bored with comparing current before and after the charge controller, I'll remove the upstream meter. I'll keep the downstream meter 'cause I like to see the cumulative power that the solar puts into the battery.