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Old 04-24-2016, 04:14 PM   #1
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San Francisco , California
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Seeking solar and battery advice: fixed-location off-grid airstream


Long-time listener, first-time caller.

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 Intíl CCD, and we are planning on parking it full time on the land as our weekend getaway spot. Itís less than an hourís 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 donít even have a tow vehicle (weíre 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 (donít 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. Thatís where we would love your help.

Iíve 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 yíall 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. Itís a temperate area ó 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 Iím 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 donít have to worry about occasionally running other random items (projector for movie night with friends! blender for smoothies the next morning!) ó but we arenít going to be running a hair dryer every day, or a microwave (I donít think!). We arenít likely to run the AC much, but the heat strip might be nice if we run out of propane ó 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 Iíd like to plan on no/minimal generator, if possible.

Iím already convinced of the need for a high quality inverter / charger, so Iíve 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.

The problem with our system is that unlike most airstream users, we donít 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), Iíve 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 donít want to go much below 50%). My impression is that these batteries would last 10-15 years or more ó 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 wonít 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 ó maybe even in a box built outside the trailer, right next to it.

So how many panels would I need to generate the needed amps to properly charge these batteries? Iím 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 ďset and forgetĒ general approach (other than battery maintenance), oversizing things a little seems makes sense. Weíll 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.

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? Iím handy, and pretty good at following directions, but I donít want to screw up the wiring on this.

Any advice appreciated. Photo of land attached.
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Old 04-25-2016, 07:58 PM   #2
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Since your system isn't mobile and you do not have physical constraints, I would consider the larger (Yingli, Canadian Solar, Kyocera, etc.) 250 - 280 W panels for your application. This will save you some money. Four panels, 1000 W, would do nicely.

You should consider a battery monitor for your system. So add the Magnum ME-BMK option as well.

You could consider at least two configurations:a first configuration where your batteries and inverter and part of the trailer. In this configuration, your batteries are located in a battery box next to the trailer and they power the 12 V systems inside your trailer. For example the water pump, fridge electronics, fans, etc. You could always plug a backup generator into the shore power inlet in case you have a run of cloudy days. You would need to install the Magnum in the trailer and wire in the exterior solar panels.

In a second configuration, you could mount the batteries, inverter, and even a generator in a shed, off to the side of the trailer. In this configuration you would have a 30 A cable connecting the shed to the shore power inlet on the trailer. The inverter would need to run all the time. The inefficiency of the inverter would consume about 20% of the available battery capacity you have, perhaps a bit more when you consider that the converter inside the trailer will always be needed as well. The advantage of this configuration is that you don't have to do anything to the trailer - everything is in the shed. Since you also have more room, you could easily double up on your battery capacity if needed.

Just some thoughts for consideration...

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Old 04-26-2016, 12:51 AM   #3
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San Francisco , California
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Yes, the battery monitor. And I have been thinking the same thing now about the bigger panels with an MPPT controller. The Morningstar 60 MPPT could handle about 800 watts at 12v I think -- which is about the realistic real-world max output of 4 panels of 250watts each, right?

Is my thinking about battery size right, or should I bump up from 464ah of wet cells to the next step in the Trojan Industrial line, which is 695ah? I know I can only use about 50%, but I want to make sure the panel system is big enough to give a healthy a charge to the batteries. 60amps enough for both of those battery sizes?
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Old 04-26-2016, 01:18 AM   #4
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The catch phrase that got my attention was a trailer could be "stored" on the land. That means no habitation in the trailer.

Before spending another nickel, I would get a legal opinion on the local zoning laws and your desire to violate the common definition of "stored" because the local authorities can shut down the occupation of the unit in a heart beat and it can get ugly and expensive very quickly.

Also you mentioned "creative ways" to handle the black water and that also needs to be researched because without a percolation test, you do not know if the land could handle the water from both the gray and black tanks. With no "sewer" permit, the operation of a non-permitted site could become another major legal issue.

It may be your land so you get to pay the property taxes, but the local governmental unit will tell you exactly how you can use it.

In this case, getting permission is far better than thinking you can get forgiveness later after spending money for the trailer and all the power upgrades you might be prevented from using. It is California after all...
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Old 04-26-2016, 04:23 AM   #5
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Ditto to switz's sage advice IMO. All if would take is one cranky neighbor, or even a drive-by eco-warrior, to shut down your residential use of the trailer on this site. As you mention, the CaCC is rigorous, and this is probably not the first time someone has tried to use a stored trailer in this way. Legal research may even reveal a similar fact pattern which has already passed/failed judgment from on high.

Would not want your investment to be for naught . . .

Good luck!

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Old 04-26-2016, 05:11 AM   #6
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What an absolutely beautiful piece of land.

I would look those zoning ordinances up online and read them thru, word by word. If there is any wiggle room at all, you will see it.

If there isn't, don't spend another dime or do one more thing toward realizing this might make more sense to haul your trailer back and forth and "camp" on weekends, than to find yourself suddenly restricted.

If it's meant to be, it will happen.

Good luck to you and your family.

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Old 04-26-2016, 06:11 AM   #7
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For a mobile Airstream, my rule of thumb is that you need at least the same number of watts of solar panel as you have amp-hours of house battery. That's based on two assumptions: (1) you will only use half of the rated amp-hours at mostó no more than 50% discharge; and (2) you will only get about 6 hours of "good"ó not peakó sun per day on average. And if your solar panel wattage exceeds your battery amp-hours, then you're less likely to discharge the batteries even 50%, and you have more reserve solar capacity for cloudy days when you get less sunlight.

Fortunately if your trailer isn't going to move, you aren't limited to the number of batteries that will fit in your trailer's battery box. You can build a freestanding battery box next to where you plant the trailer to hold as many house batteries as you want to use.

And you aren't limited to the number of solar panels that will fit on your trailer's roof. You can build a deck alongside your trailer, level with your trailer's floor, with a solid roof over it for shade in place of your trailer's awning, and cover that roof with solar panels as well.
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Old 04-26-2016, 07:52 AM   #8
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Couple of thoughts.

Consider the power requirements you need for the trailer. Are you going to need the air conditioner units? Run fridge on A/C or propane. Basically total electric? That will help you determine size of the system.

If you do not plan to travel with the Airstream then consider doing a ground based system. True off grid sticks and brick type of setup. A small shed, if allowed, to hold the batteries, controllers, inverters. Use more robust ground based systems. Allow for a 50amp power post close to the trailer so you can place the solar grid/shack where each can be in an optimal location.

Protagonist's deck idea makes sense if it is allowed and you have that inclination and the layout works.

And make sure that it is all allowed. If you have seen similar setups in the county take photos to support any requests for permits that you may need.
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Old 04-26-2016, 08:41 AM   #9
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What Switz says +3.

AND if you want more wiggle room, can you also build a Barn/stable/garage? If you garage your Airstream there it's less likely to be SEEN or noted as Occupied except of course when you are IN IT.

Another thing - vandalism. If it's really pristine and not a lot of people see it or know about it, your Airstream could become a target for theft or for a crash pad for homeless people - until they get caught - or worst of all welcome to the meth lab!
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Old 04-26-2016, 11:27 AM   #10
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No advice on the power issue; however, speaking from experience in North Georgia, we too had an issue with septic constraints. We opted for a Nature's Head composting toilet that has been great. We use maybe twice a month and usually only two people. We have had it for a year and still have not had to empty. We use a solar powered exhaust fan that runs constantly and there is less smell with this set-up than there is with a traditional residential toilet
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Old 04-26-2016, 11:48 AM   #11
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Another idea, wind generator to augment the solar on those foggy weeks of June gloom. Also could be a marine item depending on scale of your power system.
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Old 04-26-2016, 11:10 PM   #12
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Wow thanks for all the replies! All thoughtful feedback, a lot of which has indeed crossed my brain already (except the solar stuff, which I'm still figuring out, obviously).

Perc tests already done and looks good, but installing septic means permits, means at least a year of waiting. The natures head composting toilet is available today! And if we try to build an actual STRUCTURE (barn, etc.) we will have to deal with years of permitting probably.

There are quite a few trailers on pieces of land all over this area, including a modern airstream in the immediately adjacent property, used for the exact purpose I'm looking at. Doesn't mean it's perfectly legal, but also seems to indicate that it is generally tolerated and not a big deal. Proving habitation is quite difficult, actually, unless someone wants to do a stake-out.... As far as vandalism, it's not really the meth-type neighborhood -- just over the hill is Woodside, where Larry Ellison and many of the other richest people in the world live. I plan on installing some remote-monitoring security systems, but it is a pretty tame area. Generally speaking, I appreciate the words of warning, but I'm confident about these aspects of the plan. It's gonna have a soaring view of the beautiful valley, and we'll ride our bikes 5 minutes to the beach, and unicorns and rainbows will come pouring form the sky. I promise.

Back to solar/batteries: I indeed will have the solar array on the ground, with 200-250v panels, and perhaps a battery box next to the trailer, but I want to keep it pretty minimal so it doesn't look like I am doing a lot of "permanent construction", which could raise issues. The deck sounds nice, but I'm afraid that starts to get into the territory of "requiring a permit". I think we will run fridge on propane and keep a good stock of propane on site, and probably never run air conditioning. This coastal area never gets real hot. That will keep the electric load pretty minimal. So could I get away with 464ah of wet cells, or should I bump up to 695ah? With 1000 watts of panel I could supply 60amp charging using the Morningstar MPPT. (by the way, has anybody used the Magnum MPPT? might be overkill, but it would play nice with all the other magnum stuff and is only $150 more than the morningstar)

My big question now is how much to DIY. I'm a pretty careful and confident DIY person, and have experience with low-voltage electric work (from working in recording studios) but I don't have a lot of experience with actual voltage. I could hire someone to design it (or buy a kit) and then try to follow instructions carefully, supplementing with all the great photos of other people's installations, etc. -- but I'm worried that a mistake in this area would be too costly to merit the risk. Perhaps better just to leave the whole thing to a pro. I'm curious how many people who did the DIY version had a ton of background wiring real voltage, etc. I know kits like from AM Solar seem to have lots of detailed instructions, and all the correct components. It is, relatively speaking, a pretty simple electrical system, if designed correctly. I know my design is going to be a bit of a mutant hybrid between an airstream installation and an off-grid house installation, which means straying from the pre-set kits I guess. Anybody want to chime in for or against DIY here?
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Old 04-27-2016, 12:12 AM   #13
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Seeking solar and battery advice: fixed-location off-grid airstream

We did a DIY kit from AM Solar. Was easy to understand and worked as advertised.

My son, the Army nurse and I did the work. It's mostly mechanical. That said, I'm an engineer with a lot of electrical and electronics knowledge, so YMMV.

Need a few others with different experience and education to chime in here.

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Old 04-27-2016, 04:00 AM   #14
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Being a Ham puts us in a different class of electrical knowledge than some folks.

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