[Zeppelinium]

if you're going to watch TV or do other electronic things in the evenings, start by computing your required Watt-hrs. Typical lights are going to require 30 Watts, incandescent or flourescent, and you'll average two of these for 4 hours--240 Wh. The TV, if it's a small, efficient one, will need 70-100 Watts, also 4 hrs--400 WH. Water pump takes a lot, but runs for very short periods, so maybe 50 WH. If you're heater is running, I'd give it 50 Watts intermittently, say 100 WH. That's 740 WH, or 65 Ah. I use basic lead-acid batteries and they typically provide 95-115 Ah, but you can only use 80% of that safely without damaging the battery, so 78-92 Ah is what you'd have available from even a "primitive" battery. But that's only from, say, when you start cooking to when you bag it. If your heater is going to run during the night, oh oh, out of Amps. And only for a equinox day. For winter days you'll use more Wh, summer ones, less. Bottom line, two glass mat batteries will be more than enough.

Now you've got to charge them the next day. You can only count on solar from an hour after sunup to an hour before sunset (the high grazing angle makes the panels way inefficient). For the remainder of the day you're only going to average 50% of the rated output of the panels, unless you have them mounted in a sun-pointing tracker. Max ouput would occur at sideral noon and less on either side of noon. I also suspect that if you mount them on the roof, they will always be horizontal, so even a 50% average output might be optimistic.

Panels are typically 15W. You need to replace 800 Wh every day. On a winter day you'll have maybe 7 good sun hours, so each panel would give you about 100 Wh, less the 50% efficiency, resulting in 50 Wh. You'd need 16 of the 15W panels to do the job. On a summer day you'd need 10 panels. If you stand the panels on the ground at the optimum angle facing south, the numbers would drop to 10 and 7 panels, respectively.

I've made a lot of assumptions about numbers of lights and hours of working/viewing, but even if you're just one person, I doubt you'll get the number of [15W] panels required down below 5. Your dealer, on the other hand, may be providing much bigger panels.

BTW, this does not include any battery draw you need during daylight hours. At the low electrical loads you need in an Airstream, you could probably keep things going with only two hours of generator every 2nd or 3rd day. If that was even $4 at today's gas prices, that's about $700/yr, and no dragging out the panels every time you relocate. Also, the panels deteriorate over time--I don't know what the current life is, but in ten years the panels might have lost 30-50% of their solar conversion efficiency.

If you run this by your dealer and get vastly different numbers, I'd like to see the logic. My info is a bit dated and I'm thinking things may have improved significantly.