Efficiency of flat fixed solar vs adjustable portable?

[Bosque Bill]

An idea from the RV world many RVers use a filled 1 gal. water jug to hold down their satellite dish, so not much weight to carry, but wastes a gallon of water that for boondocking will not work.

A good idea. I carry a few gallon jugs with drinking water to supplement the water in the camper's tank, so that would easily work for early part of trip. I suppose grey water would work for later parts of the trip as I drain that into a gallon jug, too. Thanks for the tip.

My "portable" is not really a portable, but a panel wired to the house charge controller. I bought a controller that I could expand up to 400w, which makes adding a roof panel feasible (plus the fact that I had FWC add wiring and a roof plug when I bought the camper.)

p.s., still looking for recommendations for air gap between roof and panel frame, if you'd care to share your ideas.

 

[JaSAn]

. . .
p.s., still looking for recommendations for air gap between roof and panel frame, if you'd care to share your ideas.

The leading edge of my front panel is 1 inch above roof, the back edge is 2 inches (something I wouldn't do again). I see no increase in temperature on the ceiling under the panels at 90ºF in full sun, measured with an IR gun. Tilt probably helps a little with heat escaping.

The front panel is 10 inches behind the leading edge of the camper. I get no bugs on the front edge of the panels while the front of the camper gets quite a collection; leading me to believe that the windshield/front of camper pushes the air stream over the top of the panels. It's not affecting my gas milage any.

jim

 

[Bosque Bill]

The front panel is 10 inches behind the leading edge of the camper. I get no bugs on the front edge of the panels while the front of the camper gets quite a collection; leading me to believe that the windshield/front of camper pushes the air stream over the top of the panels.

A very useful observation. I hadn't considered that deflection aspect. OK, I'll give myself a bit larger air gap to insure cooling of the underside of the solar panel and not worry so much about drag. Thanks, Jim!

 

[Rockcod]

Squatch and Bosque Bill,

An idea from the RV world many RVers use a filled 1 gal. water jug to hold down their satellite dish, so not much weight to carry, but wastes a gallon of water that for boondocking will not work. Tent stakes makes more sense but a PITA every time you move the portable.
I guess it beats shattered glass.

Rockcod,

I also use my portable in my Class C motorhome that does not have permenant solar so I will be keeping the solar controller on the portable even though I have a Zamp Solar controller for the fixed panel on my WTW rig. I like the flexibility of leaving the controller on the portable even though you can wire directly to the fixed controller.


UPDATE: Because I could not find a 160w flexible panel for a reasonable price I have opted to go with a popular 120w Cynergy panel from Solar Blvd. at $139. If this proves to be to small I'll be able to add a second panel, have 240w on the roof and still cost less.

Thanks for the info, I'll start with 250 watts on top and two batteries, it's wired for a portable so I can grow if needed, I'll be spending time in foggy skys, curious how it will charge. A flex panel @ 120 w would be a pretty lightweight addition if needed.

 

[Bosque Bill]

Thanks for the info, I'll start with 250 watts on top and two batteries, it's wired for a portable so I can grow if needed, I'll be spending time in foggy skys, curious how it will charge. A flex panel @ 120 w would be a pretty lightweight addition if needed.

I was amazed at how much my polysilicon panel's output dropped with even fairly light high clouds. Other technologies may differ.

 

[Squatch]

Not sure this is the right time/place to ask, but are most running the portable panel through, the house controller or an independent controller supplied with the portable .?

Thanks

I have a roof panel and a connector at the rear of the camper for the portable. I made my own suitcase portable. Both panels go through the Bogart SC2030 controller I installed in the camper. The roof and the rear connector for the portable are wired in parallel and go through a 30 amp breaker prior to the charge controller.





Thanks for the thoughts on weighting the panel. Reality is I probably won't carry the portable much. the 160 on the roof has had no issues keeping the battery charged.

 

[Rockcod]

I was amazed at how much my polysilicon panel's output dropped with even fairly light high clouds. Other technologies may differ.

That is one concern, I was amazed when I saw how much the output dropped by partial shading.

 

[Rockcod]

I have a roof panel and a connector at the rear of the camper for the portable. I made my own suitcase portable. Both panels go through the Bogart SC2030 controller I installed in the camper. The roof and the rear connector for the portable are wired in parallel and go through a 30 amp breaker prior to the charge controller.





Thanks for the thoughts on weighting the panel. Reality is I probably won't carry the portable much. the 160 on the roof has had no issues
keeping the battery charged.

I will probably install an upgraded controller from the OEM version my camper comes with, and I sure like the reviews and posts here about the info the trimetric battery monitor provides. I'm one of the "loves to know what's going on gauge types " Less than two weeks out.
Thank you for the pictures and info

--Rock

 

[Squatch]

Love the info the Trimetric provides. Even in Dummy mode it tells you what you need to know. Easy to watch the draw of fridge and furnace and such.

 

[ETAV8R]

This link has a ton of info. I read most of the links a couple years ago. Handybob solar is also a great resource. He mentions that if you even cover up a small portion of a panel with shade it decreases output by something like 70%.
http://forum.expeditionportal.com/threads/60087-Solar-Power-FAQ


Last month I was in Death Valley. Upon arrival at the campsite I heard a weird noise as I begain to empty the camper. Once I removed my 100w panel I saw what the noise was. The glass was broken. Somewhere along the journey to camp the panel frame had bent, thus fracturing the glass.

The next day I moved again to a different location. I unloaded the camp gear again and began to set up camp. I decided to move the camper for shade reasons and forgot the panel was in front of the truck. This time the panel damage was my fault. I checked at the CTEK and it was a little lower than peak. Temps were a bit high and I'm sure my 0.7w fridge was drawing much more. The 2nd night in camp I looked at the fridge display and it showed an error. I thought I checked everything and even changed the plug to the main truck plug. With no fridge I decided to hit the road the next morning. Once driving and having the alternator charging the system the fridge was working again. Had I only run the engine a little while I could have determined that my house battery wasn't being charged by the bent/broken solar panel.

I have another new 100w panel at home since my original calculations per the reading in the first link suggest to double what you think you will need. This was mentioned in this thread already. Two 100w panels are quite heavy and getting them in the camper is a PIA so I did a few trips with only one panel and it has worked well up to this past trip.

In camp I tend to move my panels during the day to chase the sun. It really isn't a big deal if you are able to orient your rig and don't have a lot of tree cover, i.e. desert. I've not had to deal with a lot of trees yet since most of my trips are to desert areas. After the last trip however I did start wondering about mounting a panel to the Yakima tracks up top. I'd like to have the ability to angle the panel too. If anyone has come up with a fairly inexpensive DIY it would be great to see how to do it.

 

[craig333]

Its been cloud and rainy lately so I've seen what my system can do. With the fridge empty and coolish temps even in heavy cloud cover and rain I get enough of a charge to just barely maintain the draw. Output seems to vary from about a third to a quarter of full output. Its better than I expected especially as I don't expect to camp in prolonged bad weather all that much.

 

[Rockcod]

Its been cloud and rainy lately so I've seen what my system can do. With the fridge empty and coolish temps even in heavy cloud cover and rain I get enough of a charge to just barely maintain the draw. Output seems to vary from about a third to a quarter of full output. Its better than I expected especially as I don't expect to camp in prolonged bad weather all that much.

Well, I was hoping for better than 1/3 to 1/4 charge rate. I suppose, generally speaking, it's cooler with fog than without. That would certainly help some for refrigeration. Sooo, running the truck motor and having a quality charge relay is no doubt a good idea..

 

[Esus]

p.s., still looking for recommendations for air gap between roof and panel frame, if you'd care to share your ideas.

I did quite a bit of research and thinking on this for my current install as well. I noticed that two of the 120 watt Solar Cynergy panels mounted end-to-end length-wise added up to nearly the length of the camper roof (I have a Fleet). In fact, there was just enough space left to add one flexible 50 watt panel - so why not for an extra $90. So I have 3 panels, 290 watts total.

I wanted an air gap to prevent panels from overheating, I wanted them to be removable in case one broke and I needed to warranty/replace/etc, and I didn't want to put any holes in my roof. After digging through every post on just about every forum, I came up with the following:

2X - 8mm clear Twinwall Polycarbonate, 2' wide x 6' long
2X - Weld Mount .75" Tall Stainless Stud w/#10 x 24 Threads (10 pieces)

I used JB Weld to glue the panels to the twinwall polycarbonate. JB Weld is very strong (~4000 PSI) and rated for temps up to 400+ F. I drilled holes through the polycarbonate where the eyelets on the panels are. Then I used more JB Weld to glue the stainless weld mount studs to the roof. Locking nuts and washers to secure the panel/polycarb combo through the eyelets to the weld mounts. Boom.

While only 8mm thick, there are two layers of polycarbonate and air between them. I think that will suffice and it was inexpensive and light. Assuming that JB Weld Mount doesn't fail, the total of 16 eyelet/bolt combos ought to hold it down even in highway winds.

We shall see... just finished up the install this weekend. Have yet to put it through the paces. I'm going to do a build thread with pics after I wrap a few things up. I have the victron/bluetooth monitor as well, so I should get good data on the setup.

Also, I second JaSAn's comment about LiFePO4 battery and roof mounted flexibles for best setup with respect to weight.

 

[takesiteasy]

I like your mounting idea. I will be interested to hear how it works out over time. Nice, lightweight approach.

 

[Vic Harder]

airflow through that twinwall .... will that be enough to cool the back of the pv panels? Heat is your enemy!

 

[cwdtmmrs]

Why even bother with the twinwall? Just put a nut on the weld stud under the panel.

cwd

 

[Esus]

Why even bother with the twinwall? Just put a nut on the weld stud under the panel.

cwd

The twinwall is a lot more rigid than the panel. I don't want panel flexing and blowing around. Seems stronger and more stable this way.

 

[Boonie]

Esus,

It seems that as far as rigidity goes, mounting the panel to the roof or to the thinwall, you still have only the studs holding down the panel.

My thought is to use 3M VHB down each side and a strip down the center, definitely more rigid but far less airflow only 1.1mm thick. I will be watching your results to see if 8mm (5/16") works without a problem.

 

[Boonie]

Ok, let's talk about airflow. What difference does it make to have a rigid solar panel made of a 1" aluminum frame mounted 1" off of roof vs a flexible panel mounted directly to the 1" aluminum roof frame with endless space under it. Wouldn't direct attachment allow the larger surface of the roof act as a heat sink to dissipate the heat? If the heat would be convected thru to inside the camper what would that heat gain be?

If it hasn't been done already, it sounds like a test of efficiency of a flexible panel mounted directly to the roof compared to the same panel mounted 1" off of the roof (well, why not 6")

 

[Bosque Bill]

Ok, let's talk about airflow. What difference does it make to have a rigid solar panel made of a 1" aluminum frame mounted 1" off of roof vs a flexible panel mounted directly to the 1" aluminum roof frame with endless space under it. Wouldn't direct attachment allow the larger surface of the roof act as a heat sink to dissipate the heat? If the heat would be convected thru to inside the camper what would that heat gain be?

My guess, as a retired engineer, is that instead of heat flow from the panel to the roof, you would get heat flow from the large roof area, exposed to the sun, to the panel (plus whatever the panel absorbs from the sun.)