Travel Trailer (TT) Solar Project, Part One: Defining Needs and Scope

A simple project that saw cost and function creep the more I looked into it. 

Warning:  This essay is very pedantic on purpose; I wanted to capture my thought process.  If you wanted travel and/or hiking, come back later!

I needed to up my ability to “Dry Camp” with my TT for longer periods, and solar is a major step for that.  I originally envisioned a folding-suitcase solar charging system that I could easily store, yet pull out to charge the TT batteries whenever I stopped.  The 100 watt folding systems I’ve seen would seem to be perfect.  Digging into the specs, however showed they output 5.5 amps at best.  (Not the 8 amps you’d think, given they are two 50 watt panels.  The problem being the PWM controller)

The TT has two large 6 volt golf cart batteries wired in series for 12v.  These give me 225 amp/hours (AH) of reserve, which is decent.  However, they NEED a correspondingly large charging system; up to 30 amps with a minimum of 15 amps.  The battery charger built-in to the TT puts out only 10-12 amps, which takes forever to bring the batteries up to charge. 

Aside from the limited charging current, there is a fatal flaw with portable panels:  I’d have to leave them outside ALL DAY to charge the batteries, and theft was a real concern.  $300 in portable solar panels would be too much of a target for people to resist.

So I’m back to installing solar on my travel trailer, and I’m actually OK with this.  I intend to sell the trailer at some point, and already having solar is a check-off item that may convince the buyer to grab it.  I won’t make the money back, so I should do what works for me. 

So the question is: How big?  Well, that’s surprisingly complicated!  Load wise most of the trailer runs off 12 volts; such as the lights, water pump, bathroom and heater fans.  These are required for everyday living.   I have survived up to four days on just batteries several times, but it’s tight and I’m actively being conservative.  And, I’ve always wanted the option to run an inverter for those things that just don’t run on 12 volts. 

There are just few items built-in to the trailer that require 120v AC to operate:

  • Air Conditioner:  2,500 watts
  • Microwave:  1,100 watts
  • TV and Soundbar:  200 watts
  • DirecTV Satellite receiver: 150 watts
  • Bluray Player: 50 watts

Of the five, the entertainment equipment are the only things that are possible to run off my batteries using an inverter.  So adding a 1,000 watt inverter is going to be part of the package.  (Oh, for the purist: I know a TV isn’t really camping.  But when I’m away for weeks or months it’s really nice to have!)

After reading tons of material, I found a rough estimate of 150-200 watts of solar panels to every 100 Volt/Amp (VA) of battery to be a guide.  Since I already have 225 VA of battery, I shouldn’t go smaller than 300 or larger than 400 watts in panels.  Going larger would entail expanding the battery capacity, and that raises too many issues in cost and weight.  (125lbs for two more Lead-Acid batteries, making 250lbs total for just batteries.  Ouch)  The maximum capacity I have roof space for would be 1,200 watts, needing 600 VA of batteries.  I just have no need for something that huge nor the eight grand it would cost!  (Upgrading with Lithium 100va batteries costs $1k each, times six)

Deciding on two panels, I looked at three sizes:

  • Two 160 watt flexible panels from eBay for 320 watts (86.2₵/watt)
  • Two 180 watt rigid glass panels for 360 watts  (91.7₵/watt)
  • Two 200 watt rigid glass panels for 200 watts  (92.5₵/watt)

There were many people strongly warning against the flexible panels, for many reasons.  Since there isn’t much difference in cost between the 180w and 200w panels, the issue of bang-for-the-buck is the deciding factor.  So I settled on 400 watts from two 200 watt rigid glass panels.  400 watts would give me close to 30 amps at noon in the summer and I would still have something going into the batteries on cloudy days so I can stave off running the generator longer.

The last item is the Charge Controller that converts the power from the panels to something the batteries eat.  Being a geek, I chose a controller with Bluetooth!  <Geekgasim!>  Being able to monitor the system while eating lunch just sounds too cool.

The base equipment thus far:

  • Two 200w panels
  • 30 amp MPPT Solar Charge Controller
  • 1,000 watt Pure Sine Inverter

Simple!  Piece of cake, right?

All except for those pesky details…

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