Solar Panel Placement

[rickeieio]

We're contemplating several additions/modifications to our rig.  They include adding a small freezer in the garage, and solar panels to keep the batteries topped up on both the truck and trailer.  It just occurred to me that there's a large area going unused behind the sleeper, but above the car. One could build a flat "carport" roof of roughly 8'x8' and cover it with panels, mount the electronics inside the cab, and just run a cord to the camper. 

Plus side:  Don't violate camper roof.  Area can be flat for ease of mounting. Shady place to sit when car's off. Keeps batteries charged on both units.  Would likely make enough power to run most (small) items in camper.  Perhaps most importantly, runs freezer, furnace, electric blanket while in motion.  ( It's nice to crawl into a warm bed when travelling in cold conditions.)  

Minus side:  Need to park units close to each other when not hooked up if boondocking.  One more item to hook/unhook.

Questions:  How many watts would 64 ft/sq produce under average conditions?  What would this cost?  Am I really just crazy for even thinking about this?

BTW, a small house type freezer might cost $300.  A similar sized RV freezer is around $1,500.  That leaves $1,200 to play with.

[Darryl&Rita]

Perfect world, assume 15 watts per ft2. Real world is closer to 8-9.

[Randyretired]

Solar panels are relatively inexpensive.   There are even some used panels available.  Santan Solar in AZ has some pretty good prices on used and new panels to start your search. Finding the right size panels to fit your area takes some time but my recommendation is to buy as many panels as will fit.  A charge controller will be needed and an MPPT controller is best  It will change the voltage from the panels to meet your batteries needs.  This allows the use of higher voltage panels.  One thing is that 12v circuits need fairly large wire to carry power even short distances.  For larger solar setups the batteries to store the energy can be the most expensive items but if you only need to keep your batteries charged that isn't an issue.

[GlennWest]

Problem I would have is truck has to be parked away from me at most RV parks. I just use a small panel on mine to keep batteries charged up.

[Chad Heiser]

A 365 watt panel is approximately 40" x 80".  So you could get two of those on an 8' x 8' square.  That's 730 watts rated output.  Expect 80% of that in ideal conditions (mid summer, high noon) for flat mounted panels.  Expect 50% or so in winter.  Now you are looking at 360 to 580 or so watts depending on time of year.  A typical solar day is 5 hours of full production.  Now you are looking at 1800 to 2900 watts of production a day (for ruff numbers).  Figure out what your loads are going to use and compare the two numbers (production vs. usage) to get an idea of what they can do.

[rickeieio]

My prime concern is running the freezer and maybe the electric blanket while travelling, and not depleting my house batteries (4 deep cycle).  Keeping the truck and trailer batteries topped off when in storage is a secondary matter, but still important.

Maybe I don't need the solar at all. Might my house batteries last 10 hours with the intermittent 15a/120v freezer and a couple hours of the 15a/120v blanket?  If freezer runs 2 hr that's 3600 watts and blanket also for 2 hr is another 3000 watts.  If batteries are 500a/h that's 6000 watts x 4  = 24,000 watts, of which 1/2 is available?  Am I worrying about nothing?

[Randyretired]

I am wondering about your batteries.   What type and size of battery do you have?  500ah batteries would not be typical RV batteries. Also the loads you have calculated seem high.  The freezer runs for a period of time and then goes idle for some time before the cycle repeats.  The energy guide should detail the total amount of power annually.  From that the amount of power per day can be roughly  calculated. 

Edited January 6, 2022 by Randyretired

[Chad Heiser]

1 hour ago, rickeieio said:

My prime concern is running the freezer and maybe the electric blanket while travelling, and not depleting my house batteries (4 deep cycle).  Keeping the truck and trailer batteries topped off when in storage is a secondary matter, but still important.

Maybe I don't need the solar at all. Might my house batteries last 10 hours with the intermittent 15a/120v freezer and a couple hours of the 15a/120v blanket?  If freezer runs 2 hr that's 3600 watts and blanket also for 2 hr is another 3000 watts.  If batteries are 500a/h that's 6000 watts x 4  = 24,000 watts, of which 1/2 is available?  Am I worrying about nothing?

Your numbers are a bit off.  A 15 amp at 120 volt load is 150 amps at 12 volts.  The inverter will pull 150 amps of 12 volt to produce 15 amps of 120 volt.  It will actually pull a little more due to inefficiencies and conversion losses. 

[rickeieio]

Duh.  It was past my bed time when I was typing and the brain was already half asleep.

But, I still have to wonder, would the house batteries run the loads and still have enough to allow us to run the jacks and such to set up at the end of the day?  I'll check today and see what the batteries are rated, but they're 4 deep cycle lead/acid.