Placement of solar panels on roof of 80s Keystone

[philos65]

View attachment Camper roof 2.pdfView attachment Camper roof 3.pdf

I'm deciding how to mount two solar panels on the roof of my 80s Keystone. The panels are 35" x 65.5" and 40 lbs each.

https://www.batterypete.com/batteries/240-watt-solar-panel-rec-solar-rec240pe/

There are two options. I've attached drawings of the options.

I'm wondering which is better, and why.

My first inclination is to mount them fore to aft. My main reason is that I will be installing brackets to tilt the panels when parked. It would be a one person job if the panels are mounted fore to aft.

I will be screwing 1" aluminum box tubing to the roof to support the panels

Thanks for looking at this and offering opinions...

Jeff
Laramie, WY

 

[ckent323]

Jeff,

I had a 1987 Keystone with an FWC carrier rack on it but never had solar panels. It had two roof vents. So I am familiar with your camper. My front and rear lift panels were starting to delaminate so it did not put any extra weight on the roof.

I presently have a 2007/2008 Keystone which has 2 roof vents and full length Yakima racks. I mounted the solar panels to the Yakima racks in an arrangement similar to as shown in your version 3. That is, one panel transverse between the two vents and one transverse aft of the rear vent. My aft solar panel does not overhang the end of the camper.

I put the roof penetration and Go Power Solar Cable roof penetration box under the panel that is between the two roof vents (My camper was pre-wired so there were already wires there). I like having the roof penetration under the panel for the little bit of extra protection from rain, branches and whatnot.

My first thought is the overhang from the aft panel on your camper would help shield the rear entry during rain. It would be somewhat exposed to damage while backing up however so that is something you should consider (I backed up and broke one of my rear floodlights on a low hanging tree branch that was above the field of view of my rear view mirror awhile back). It would probably be better if it were mounted to be no more than flush with the end of the roof.

Weight wise I don't think it would make much difference if the front panel were mounted transverse in front of the front vent instead of between the two vents (I have similar suspicions relative to moving the rear panel to the front)

As for the configuration two I can't help but wonder how 80 pounds on one side of the roof might impact lifting the roof and loading the lifting panels.

Hopefully someone else has done that approach and can give you better insight.

Regards,

Craig

 

[AZ_Nick]

I added extra cross bars and mounted mine to the left side so I could still hold a canoe on the right, similar to your roof 2 layout. This will keep your options open for carrying other stuff on the roof. The extra weight was the final straw for me adding lifting struts(40# rear / 30# Front). Here's a picture, this was a 80's Keystone before the remodel, still a 80's Keystone roof. Mine are 100W panels because I wanted to keep everything 12V.

 

[philos65]

Thanks for the replies. A couple points in response to Craig and AZ Nick.

I tore out the lift panels and will be fabricating an EMT lift mechanism that will go on the short sides above bed and door.

I have 60 lb and 40 lb lift struts I'll try til I find a good combination. I can see the 60 lb struts on the heavy side and 40s (or maybe 30s) on the lighter side if I put the panels fore and aft rather than across the roofs width.

I can also put the EMT lift mechanism above bed and door, and struts on the long side. Don't know which would better. Perspectives?

Two maxxfans will go in the vent holes adding another 30 lbs or so.

The roof itself seems to be about 60 to 70 pounds.

I'm mounting the aluminum box tubing on the roofs edges. Depending on how much that tubing flexes, I might have to add supports similar to what AZ Nick did in the picture above. The fore/aft configuration is likely to have this flex. I figure putting the weight on the edges of the roof will be sturdier while driving than mounting the panels to the fore/aft roof tubing.

The camper is at least 30 years old and the roof is definitely not factory perfect. I'm not too worried about the 5" overhang off the rear as I'll be hanging stuff off the back of the camper while driving that'll be more than 5" deep.

The solar panels are 12 volt. I use a CPAP machine with humidifier that draws 6 amp hours - 48 amp hours a night. Hence 490 watts of solar panels.

Again, thanks for perspectives and thinking out loud. Jeff

 

[ckent323]

Jeff,

There are portable, rechargable batteries available for CPAP machines. They are not particularly cheap ($150 and up) but are modest in size and can last up to two days (with the humidifier off or turned down to lowest setting).

For sure they are cheaper than solar and can be recharged from a 12 V or 110 V source. Even with solar maybe a good backup in the event the batteries get pulled down, or even as the primary CPAP power supply with the camper house batteries as backup.

Unfortunately we do not actually get to access all the power available in a battery without reducing its life (or even permanently damaging it by drawing it down too far).

Keep in mind that if you want long life from your house batteries you should not discharge them more than about 20% - 30% on a routine basis if they are AGM or FLA type. Pulling them down further on occasion is OK, but if you do it routinely you can reduce the battery life by as much as a actor of 3x or more (1/3 the life or less)

If you have not done so already look carefully at the Depth of Discharge vs Lifetime (number of charge cycles) for the battery you choose for your storage bank.

If you choose deep cycle AGM or FLA you are probably going to need at least 200 AH of capacity to deal with 48 AH a night (and that is with little or no margin and no other power draw like lights, water pump, etc). LiFePO4 can handle deeper routine discharging to more like 50% on a routine basis so you might be OK with 100 - 150 AH minimum (again with no margin and no other loads).

Prematurely killing your house batteries after 400 cycles (instead of 1200) vs killing a perhaps less expensive portable CPAP battery ove the same number of discharge/recharge cycles is worth thinking about.


Regards,

Craig