Community Forums

BillJinOR · 12-16-2016, 02:43 PM

Just a point .. and opinion. I have 8 panels on my roof 4 z bracket per panel dicor under the bracket 2 - 3/4" screws into the roof and dicor over the screws. I have had no problems whatsoever in fact I left ( forgot ) my voltmeter tool laying on the roof next to the panels and drove a entire day to find it lying in the same place! I think the air "forces" you are afraid of don't exist. The second point I make is that I studied installs of , and asked for info from professional installers. None "0" of them use "air dams " in fact one of the top installers just uses 3m tape to a fiberglass roof not screws. But hey as said , they look cool and quess it can't hurt , right?

Timon · 12-18-2016, 12:22 PM

Quote:

Originally Posted by LarryW21

Timon, interesting points. Wouldn't we want no upward or downward air pushing our solar panels? Sooooo....wouldn't no dams facilitate that best?

Actually when you look at panels the frame creates a pocket which might create low pressure under the panel when the panels are close to the roof. When mounted close I don't think air dams do much. Now if your panels higher up so they are about equal to say your AC units an air dam may be useful.

Quote:

Originally Posted by BillJinOR

Just a point .. and opinion. I have 8 panels on my roof 4 z bracket per panel dicor under the bracket 2 - 3/4" screws into the roof and dicor over the screws. I have had no problems whatsoever in fact I left ( forgot ) my voltmeter tool laying on the roof next to the panels and drove a entire day to find it lying in the same place! I think the air "forces" you are afraid of don't exist. The second point I make is that I studied installs of , and asked for info from professional installers. None "0" of them use "air dams " in fact one of the top installers just uses 3m tape to a fiberglass roof not screws. But hey as said , they look cool and quess it can't hurt , right?

I tend to agree with close mounted panels and yes they look cool.

Reed Cundiff · 12-18-2016, 01:37 PM

We passed through Isthmus of Tehuantepec (sic) two days ago and the winds are world famous. Metal on edge of 315 W panel tore and we lost 3 of 4 attachments. Side winds were probably in excess of 60 mph steady. Note that Roadtrek seems to use air dams with their solar panels. The concave shape at sides of Roadtrek may have aerodynamic effects. Younger son and family will fly down to Cancun on Christmas Day and hopefully will have replacement parts. The mounts remained strongly attached to vehicle

Reed Cundiff · 12-18-2016, 01:44 PM

They had seven semi rollovers in one day due to winds in the area we had the problem

harryn · 12-21-2016, 01:29 PM

That is some serious wind. We get some high winds in the winter here, often in January, combined with the winter rains, it can force water into unexpected places.

rdh8 · 12-21-2016, 08:19 PM

Quote:

Originally Posted by drdarrin

I did wire them in parallel and I used 4 gauge wire from the roof to the disconnect and charge controller. My panels are 2" above the roof on the edges and less in than that in the center since the roof is curved. We've been very happy that we can run our toaster and microwave off the inverter. For minutes obviously. So far, we're very happy not to have to depend on shore power or our generators for 120V. The generators are for backup only now.

I hooked mine in series so I get 80V in full sun.
Using the higher voltage cuts the current in half reducing losses.
My MPPT takes care of converting down to charging voltage at 30A.
And I even get a nice trickle charge at night if I park under the street light

That's because I have double the voltage having my panels in series.

Robert

LarryW21 · 12-23-2016, 09:40 AM

Understood, RDH, but those of us who camp in the trees are concerned about shutting down the whole system with just a little shade on one panel. I went parallel.

Timon · 12-23-2016, 04:54 PM

Paralleled panels require a larger gauge cable the more power you produce which raises cost.

Series panels can use smaller gauge wire for the same power level but shading kill the whole string.

MPPT controllers are more efficient when they have higher voltages to work with.

So in general you want the highest voltage you can run with a manageable wire size. Most RV with prewired solar come with 6AWG or less cable.

With low voltage panels that requires many panels in series which means shading problems are more pronounced.

There are solutions.

Find small high voltage panels. I've never seen any.
User larger high voltage panels.
Combine several low voltage into series groups then parallel those groups.

The third solution is the most reasonable for most RVers. Running 4 100W 24V panels will give you 400W at 96V at 1/4 the current of 4 in parallel. You then parallel multiple of these series groups.

You will still loose 4 panels if one of them get shaded but you'll still have the other groups. So it's a compromise between heavy cables, less shading effects and MPPT efficiently.

Real world example, if you wanted 1,200 watts of solar and use 24V panels in parallel that's about 50A through the cable but at 96V that's only 12.5A.

Personally I thing shading really isn't As big a deal as it's made out to be. If your in the forest you'll not be getting any sun and if out in the open you'll never get shaded. If your at an RV park you don't care.

Reed Cundiff · 01-20-2017, 04:56 PM

Agree with Timon as we have 90 V to controller on fifth wheel but only 12 V on Roadtrek; economy of scale.

Younger son and family spent a week with us on beach in Yucatán and we redid the torn off panel. Do not get much solar with panel lashed to rear if Roadtrek. Had to spend time wandering around Playa del Carmen and bought 1.5" aluminum extruded aluminum L channel. Bolted 5' section to either side of panels. Placed 1" x 5' aluminum strap inside panel attachments to make sure the bolts did not tear light aluminum if the panel. Then bolted another 5' to the the above and then bolted and silicone glued the whole thing to roof. This should work and effectively have air dam to side wind

wizechatmgr · 02-12-2017, 05:09 AM

Great thread here.

One other consideration - you actually want airflow under your panels while they are producing. Generally the hotter they get, the less they produce.

Proper mounting should make it nearly impossible to lose one to wind - short of your fifth coming off the ground.

I know Outback is extremely expensive but they make some great equipment.

vsheetz · 02-12-2017, 07:02 AM

I have a very busy roof, with lots of equipment lined up down the middle - three air conditioners, etc. I installed fifteen narrow 100w panels mounted mostly along either sides. Basic Z brackets so a few inches off the roof. No dams. Wired as three strings, using #10 wire, to a combiner box with circuit breakers / disconnect located near the battery bank. So about 100 volts to the controller, and low amperage on each string. Short length of #4 wire connects to the controller - a MPPT Midnight Solar Classic 150. Then another short #4 to the battery bank. Batteries are six 6v GC2.