Seeking advice for solar and battery -- fixed-site off-grid Airstream trailer

Hi.

My wife and I recently bought 3 acres of agricultural-zoned land in a beautiful area of coastal California less than a mile from the beach. Part of the reason it is still such a pristine and beautiful area is because of the VERY intense regulation of building in the area. One day we may build a house there (it is legally allowed), but we don't have the money for that now --and the red tape involved in that process will be insane and very very slow (coastal commission of CA is notorious).

But of course, we can put a mobile home there, legally, "in storage". My wife and I recently bought a 28' 2005 Airstream Int’l CCD, and we are planning on parking it full time on the land as our weekend getaway spot. It’s less than an hour’s drive from our house so we will be going there almost every week. We really don't plan to travel with the airstream, at all. We don’t even have a tow vehicle (we’re hiring someone to deliver it). I know that will shock some of you. We can do composting toilet or some other creative ways to deal with blackwater (don’t ask). We have a water well on-site, but no power. It will take a LOT of money to hook up power to the grid for the site, so we are hoping to design a solar battery system for the airstream instead. That’s where we would love your help.

I’ve been reading and researching for a long time on this site, and on other solar off-grid sites (and on some sailing sites, where they also deal with need for off-grid power) but I wanted to see what y’all think we should do, as far as a solar and battery system. The area is on a sunny hillside with a 13% grade facing east. From my research online it looks like the area gets 3.2 peak sun hours in December, and 7.7 peak sun hours in July. pvwatts puts it at about 3.4 kwh/m/day in December up to 6.75 in July. It’s a temperate area — average lows are around 42 in the winter and average highs are around 64 in the summer. So we will be running the furnace (runs on propane, but the blower uses electric), but then of course there is the water pump, the lights (we will replace with LED), the stereo system, fridge (runs on propane), propane detector, our laptops, fantastic & bathroom fans, phone chargers, and other stuff I’m probably not thinking of. Most people say this is about 40-60 Ah per day, it seems. I would like to design a system that can run without generator as much as possible, sized big enough so we don’t have to worry about occasionally running other random items (projector for movie night with friends! blender for smoothies the next morning!) — but we aren’t going to be running a hair dryer every day, or a microwave (I don’t think!). We aren’t likely to run the AC much, but the heat strip might be nice if we run out of propane — but since I know those items are extreme electric guzzlers, we were planning on having a generator as backup to help with that if necessary. But I really really hate the noise of the generator, even the nice newer ones. So I’d like to plan on no/minimal generator, if possible.

HARDWARE

I’m already convinced of the need for a high quality inverter / charger, so I’ve already bought a Magnum MSH3012M as the heart of the system. I assume I should get the remote battery monitoring kit and remote control panel from Magnum to go with it. 

BATTERIES

The problem with our system is that unlike most airstream users, we don’t plan on using a generator or hooking up to shore power, ever. Unless we really really need to fire up the generator every few weeks, just to get the batteries up to 100%, to keep them healthy. Is that necessary? In an ideal world, we would love to fire up the generator NEVER. After reading a lot about partial-state-of-charge issues with batteries (it kills batteries, except for Lithium), I’ve been leaning towards getting two Trojan IND9-6V batteries, which are flooded lead-acid batteries that are designed for serious solar use, and designed to withstand PSOC issues. That would give us 464Ah (but of course only about 250Ah usable, since we don’t want to go much below 50%). My impression is that these batteries would last 10-15 years or more — they are used in serious off-grid applications in Africa, etc.  But maybe that is serious overkill. I could do AGM but my impression is that even with Lifeline they won’t last nearly as long, and would about the same. Lifepo4 just seems to new to me to able to rely on them for 10-15 years. Normal wet cell batteries like T105s seem like they will be killed quickly by PSOC with our scenario (no shore power ever, rare to never generator usage). I know that with the wet cells there would be some maintenance involved, and they would need to be in a ventilated area — maybe even in a box built outside the trailer, right next to it.

PANELS

So how many panels would I need to generate the needed amps to properly charge these batteries? I’m assuming I will get the 100w mono Renogy panels, since they seem best bang for buck, as far as a 12v system. Maybe I should be thinking about a smaller overall system, but with the goal of minimal generator usage, and also the goal of a lazy “set and forget” general approach (other than battery maintenance), oversizing things a little seems makes sense. We’ll mount our panels on the ground close to the airstream where they can get full sun and be tilted at an optimum fixed angle. I guess I will need some kind of grounding pole into the ground somewhere too.

DOING THE WORK

I see there are some real pros doing this type of installation, but none that are super close to me. There are, however many marine electrical installers around the Bay Area here in northern CA. Should I be calling up some of those places to see about installation of this stuff? I’m handy, and pretty good at following directions, but I don’t want to screw up the wiring on this.

Any advice appreciated.