I've been talking with the support team at Grape Solar - going solar seems more and more like a no brainer upgrade at this point.
I found them at Costco - $199 shipped for 100 watt panel. This led me to find that Home Depot carries their whole line of products for the same pricing - including $399 shipped for a 250 watt panel. Amazon has the 250 watt panel for $399 with free shipping and no sales tax to California, but does not carry the 100 watt panel.
I did some emailing with Grape Solar, and found that they recommend AM Solar as their RV partner. AM Solar sells the panels for about $10 more shipped than do the bigger folks above - and they also make RV mounts and installation kits for the panels.
My thinking is to start with 200-250 watts, but design a system that will scale to 500 watts or more.
So I have a question for you solar gurus - I'm trying to figure out what input voltage to design for given the output voltage is fixed at 12'ish volts. The 100 watt panels are speced out at 17.7 volts, and the 250 watt panel at 31 volts.
I know that I could wire two 100-watt panels together in parallel to get more amps at 17.7 volts, or in series to get 35 volts. I know I can use thinner gauge wire and have less current drop at higher voltage for the same amount of power - so just looking at transmission losses and cost of wire it would be preferable to design the system to run at higher input voltage.
So my question for you gurus is about how charge controllers work vis a vis input voltage vs. the fixed 12V'ish out put voltage - I'm not finding it easy to figure out of they will run efficiently at higher input voltages. Does anyone know - will they effectively convert the higher DC voltages and send more amps to the 12V
battery system, or do they clip at some level of input voltage? I see Max voltages listed in the specs, but no discussion about the optimal input voltage ranges. I called Xantrex tech support, (their C series line seems like a good fit) but gave up after an hour on hold.
If I can optimize around a single 250 watt panel at higher voltage (at least to get started) this would seem to be the way to go in terms of price / performance - but I should not go this direction if it makes the charge controller less effective than two 100 watt panels in parallel. That's what I am trying to sort out.
Note - I invited the grape solar guys to join the Airforums and recommended they put together a special package for Airstream owners. They seemed to be interested; we'll see if they do it.