Battery current draw

So start by estimating how many amphours a day you need. You need to know the current draw on each item and the daily hours of operation for each. Multiply then add. It sounds hard but its actually pretty easy.  Here is an example showing my summertime use. Lots of amhours for fans because its hot in NC in the summer. In the cooler months fans will be off but heater will be on so it works out to be a bit less but similar. Lights are really a minimal part of the load. I have a 12V TV which is why I've included that. Easy mod if you want to watch TV in the pod off grid and save lots of energy. 

Next, battery capacity. You can see that I have a total of about 75 amphours per day. As we don't want to bring our batteries below about 50%, I need a minimum of 150 amphours to get through one day without charging. If you want to go 100% solar and never charge from your vehicle or a generator, you will need about 2-4 days storage in summer depending on where you live. While you never get a day with zero solar output, this 2-4 days gets you through longer periods of cloudy or stormy weather. I have 220Ah battery storage (dual 6V GC2's) for 110AH useable and so expect to need to use my genny fairly frequently in cloudy weather. 

On to solar sizing. A 100 watt module will not be the right answer for everyone. Your mileage will vary. The variation depends on several factors. Besides your actual loads as above, it depends on the time of year, the region you live in, whether you camp under trees or not, and whether you are manually moving around a portable solar module and keeping it pointing at the sun all day or (if you're lazy like me) have them permanently mounted to the trailer roof. 

You can figure that a 100 watt solar module will deliver about 6-7Ah for your loads from an hour of full direct (perpendicular) sunshine.  This is not 100 watts/12 volts=8.3A because of the way solar modules are rated and the charge/discharge losses in the battery.  So if you have a perfectly clear cloudless day, no tree or other shading and keep your module tilted toward the sun, moving it from east to west over the course of the day, you might get 50 amp hours from it. Where I live in the mid atlantic with solar flat on the roof I get about 30 amphours on a good summer day from 100 watts. If I'm not under trees (which I often am). So, I plan on installing a 350 watt module on the roof of my rPod, which should give my about 100 amphours a day in summer when not under the tree canopy. You can get a 350 watt module for under $200 now so why not?  I'll revert to the genny or TV charging when forest camping as needed. 

To mitigate the genny noise and smell you can get a nice 2kw inverter-generator which runs very quietly, convert it to propane, and put it  and a 20lb tank far from your campsite on a 100 ft extension cord.  That's what I do, no stink of gasoline, and I can barely hear it. Running it once a day in late afternoon/early evening when everyone is making noise and cooking helps as well.  I don't fell bad about running mine, its a lot quieter compared to the family in the next campsite with the shrieking kids and barking dogs 

Thanks for the insights.  Which charge controller are you using?

I expect that we will be setting the thermostat at about 50 degrees (during the night only in weather averaging mid-40s during the day, low 20s at night.  Reading all the responses thus far, I'm leaning toward buying a PV charging system.

50% discharge on a 12V 100AH battery is roughly 600 watt-hours. On a good summer day below the 40th parallel you should get 6-8 hours of sunshine (no clouds). I generally expect roughly 80% on our panels (we're at 37 degrees north), and we rarely have clouds in the summer. So, 80% at 7 hours gets you a bit over 560 watt hours with a 100 watt panel.

Figure out how many watt-hours you use in a day, and see if that is close. Even if it's not quite enough, it could take weeks to add up to a problem.

Many thanks for all the feedback.

I've already replaced all the incandescent bulbs with LEDs.  As an aside, my external power meter indicates that one two-bulb light fixture with incandescent bulbs uses 46 watts, while the same fixture with LEDs uses 3 watts. Quite a difference especially if you have several fixtures on simultaneously.

We never use the fridge as we use a five day cooler that does the job just fine.  The only thing I'm really concerned about is heat during cold weather, which, if we use the jumper cables from the truck method it seems like that should work just fine for a few days.  It does make me wonder about putting the extra load on the alternator while out in the boonies, though.

IMHO, generators stink.  Add the gasoline, noise, yet another thing to maintain, and more weight.  Maybe I should just go ahead and get the lobotomy now.  Nothing ruins the moment like somebody nearby running a generator so they can watch Gilligan's Island reruns or whatever while we're trying to get some sleep before climbing a 14er the following day. 

Going solar sounds like a great idea, but there are so many options my head started hurting trying to figure out the most reliable and cost effective way to go about it.  Is a 100 watt panel really enough to charge a deep cycle battery in one day if the battery is at about 50% charge?  I saw an Airstream a while back and the top was completely covered by flexible solar panels.  Obviously they are doing more than just charging a battery...

Happy camping to all.