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Old 02-08-2015, 10:45 AM   #1
2 Rivet Member
, North Carolina
Join Date: Mar 2014
Posts: 38
How Big is my Solar System?! Off grid questions...

Dear Forum folks, after many hours of reading and research, Iím seeking your assistance with my solar system education and plans! Iím full timing in a 1981 Excella (at least another year; several more if I install a little woodstove) and want to have off grid ability. Please chime in on my process, ideas, and questions below!

Iíve been taking notes but donít yet have a total number on my overall power usage. My AC load seems pretty modest...biggest pull is my Vitamix blender (.02 kwh to make a smoothie), my electric blanket that I use to heat the bed briefly before crawling into bed (.03 kwh), my beloved Miele vacuum (.2 kwh 1x/wk). My most common AC use is to charge computer and phone, and play shortwave radio (6W) and speakers (19W). My DC needs are harder for me to measure (water pump, LED lights, furnace fans in winter, two Maxx fans in summer, converter). Fridge is on propane. Not planning on using air conditioner (I survived last summer without it).

So, I want to have enough power without paying more than I need for the system. Imagining I can either take the system with me if I sell my trailer in a few years (and use for a small house) or include in the airstream sale cost. I sat down with a knowledgeable solar friend and came up with the following tentative system (prices from altEstore):

- four 6-volt, 190 amp hour AGM Deka batteries model #8AGC2 $270 each = $1080. MK 8AGC2 AGM 190Ah (20 Hr) T881 Terminal

- two 270-watt Solar World modules (so 540 watt total), model #SW70 mono V2.5, $269 each = $538. SolarWorld 270 Watt Solar Panel, Sunmodule SW270 Mono V2.5 Frame

- 30 amp mppt charge controller, 150V Midnite Solar The Kid, $315. Midnite Solar The KID, 30A MPPT Charge Controller, 150V, Black

- invertor (here Iím not sure yetÖseems I need more load numbers to decide) maybe Outback 2800W, 12V model# VFX2812, $1795. Outback VFX2812, 2800W, 12V Inverter (might be more than I need? If so, maybe the Samlex 1500 for $615 plus an Iota 75 amp battery charger converter with ds IQ4, 4 stage charging for $328)

- $500 in miscellaneous parts for installation

- thatís a grand total of $4,228!!! (without installationóplanning to have a friend help with that and barter some of that expense)

Thereís also these solar kits that the folks over at Out of Doors Mart use a lot (which donít include batteries) from Go Power (price ends up about the same as above piece meal system):
320 watt: Solar Elite Charging System (320 watts) | GPElectric (can find for about $2,700, without battteries)
480 watt: Solar Extreme Charging System (480 watts) | GPElectric (on ebay for $3680, without batteries)

Planning on housing my batteries inside, under the as-yet-unbuilt couch at the hitch end (canít remember the proper airstream term here). I just measured my battery boxes and realize that the Dekaís are too tall to fit which would mean taking the boxes off and fitting all four under the couch. Not planning to mount modules on the roof since Iíll be parked long chunks of time (in shade in the summer) and want to be able to move the panels around (pole?, lean on ground?, weíll see).

Thanks for any flags of concern (what have I missed or misunderstood) or insight (like which invertor, is this system more than I need, etc.) as I move forward!
All blessings~

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Old 02-08-2015, 12:40 PM   #2
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Chelsea , Michigan
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I'm not an expert in solar by any means but you are basically on the right track in your thought process and you are learning that it is not inexpensive to do this. You are also being realistic in that you will not be able to run the AC on solar off of batteries unless you are willing to spend a big bundle of money, get a bundle of batteries (north of 800 AH) and even then you will have limitations (FWIW, I don't know of anyone who runs their AC off batteries.) A lot of people think they can get a cheap solar system for boon docking. I wonder how many of them are disappointed in the end with their "el-cheapo" do it yourself installs after they are done?

Check out this site for a good overview and place to start:

Solar Electrical Systems for RVs | Technomadia

AM Solar (Welcome to AM Solar_Your RV Solar Specialists since 1987) is a leading supplier of solar equipment to the aftermarket RV industry. Do yourself a favor and look at their product line before you buy anything. They offer integrated kits that are proven to work together.

Three comments on the ideas in your post.

1. You will probably be able to get by with a 1,000 to 2,000 watt inverter. Look to your most "power hungry" AC appliance as a guide. You do not need to run more than one heavy load AC item at a time. Get a pure sine wave inverter so you can run your electronics without any problem.

2. If you plan to locate your batteries inside the trailer (vs. the box outside on the tongue) make sure you use batteries that do not vent gasses (e.g., wet cells) such as AGM's or Lithium Phosphate (these are the good kind for internal placement.) Using standard wet cell batteries inside the trailer is a no no for several reasons, most of them fatal.

3. Make sure your charger is a multi-stage charger to properly take care of your battery investment. I'm not sure if the model you mention is that kind of charger.

Use the search function on this site and you will find a lot of good information on this topic.

One of the members of this forum (call sign "Lewster") is an expert in this subject and, if you are lucky, may chime in.

Happy hunting and good luck!

Bob Martel
WBCCI# 5766
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Old 02-08-2015, 01:16 PM   #3
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Bowie , Maryland
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One note - look into 12 volt chargers for your cell phone and laptop. No point in converting the power from 12 volt DC to 120 volt AC, only to convert it back to DC. There are losses in each conversion.
1995 Airstream Classic 30' Excella 1000
2014 Ram 2500 Crew Cab with Cummins 6.7L Diesel

Sold but not forgotten: 1991 Airstream B190
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Old 02-09-2015, 02:31 PM   #4
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Thanks Bob and Skater!
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Old 02-09-2015, 03:54 PM   #5
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A couple of comments: Your 120 volt loads are quite modest, I think your inverter may be unnecessarily large. And, as mentioned already, charging things like phones should be done at 12v not 120. The standby inverter load would be far in excesses of the little load you put on it.

You list the Midnight Solar "the Kid MPPT charge controller" It is only rated at 30 amps and if you use two large 270 watt panels for 540 watts total you are far over the 30 amp rating. (12v x 30 amp = 360 watts) It is a good charge controller but you would need two of the for the panels you list.

Those 270 watt panels are physically large and hard to move around if you are looking at a portable system. Be sure you understand that, and how you are going to move them and set them up, and secure them. More smaller panels may be preferable to two large ones. Most of the large panels such as you list have higher output voltages, so, yes, you will need a MPPT charge controller to manage the high input voltage yet come out at the 12-14 volt battery charge voltage.

My feeling is that you are really oversizing things and don't need either the amount of panel area you have listed, nor the large inverter. Even the 4 batteries you list may be unnecessary, considering your listed loads and usage.

You need someone who can put together a well thought out integrated system for you, designed for your loads and situation. I have questions about what you are proposing and where the listed choices came from. You don't want to spend a large amount of money and not have the equipment you need to do the job you have in mind, or have too much into the system in excess o your needs.
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Old 02-09-2015, 04:21 PM   #6
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2014 30' Flying Cloud
Ponce Inlet , Florida
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Install solar controller, inverter and battery charger as close to the battery bank as possible.

Use the correct gauge wire . If you plan to have a long wire run for your panels to be in the sun you will need to take that into account. Allow for expansion if you think you may want to add more panels in the future.

Get multistage charger W/ temperature compensation. This will add life to your batteries. Did not think this was important as my batteries are inside under the couch. Until I realized there would be a 40-50 degree temperature differential from cold to warm weather camping.

Remote display panels to keep track of things are nice to have . I use mine all the time.

Agree 2800w inverter may be too large. 1000-2000W should be enough unless you have some power hungry AC loads. Unless of course you must make a smoothie while vacuuming, listening to the shortwave as you heat up your bed.

Consider converting your lighting to LED to save power

Get quality components from a reputable source. Did not look specifically at your suggested components. However, some of the stuff on ebay and the net is suspect at best.
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Old 02-11-2015, 09:59 AM   #7
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I don't have any personal experience with solar power yet. But I did read a good article about solar panel installation. You might want to check it out Welcome to Love Your RV! | Full Timer RVing Blog He worked with a kit and it didn't cost anywhere near what you are estimating. I hope it helps you.
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Old 02-17-2015, 03:30 AM   #8
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Videos by the Wynns contain lots of practical insight. Best Converter Charger for an RV - Smart VS. Dumb. Here is good information:
Marty Womer
Saco, Maine
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Old 02-17-2015, 06:21 AM   #9
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My comments (many have said some good things already):

While your components are generally fine by themselves, it looks like you went thru some web sites and chose them randomly. One of the basic tenets of a good solar charging system is to be certain that all of your components will play nicely and in harmony together.

2700 watt panels are large, heavy and not easily handled. Any portable system has unique challenges like length of cable runs, size of that cable to minimize voltage drop ad the actual connection mechanism used from the panels to the controller and then from the controller to the batteries.

While Outback is a good company, their inverters are better suited to use in stationary PV systems and not in a mobile environment. In addition, you really need a degree in electrical engineering to operate and understand their 'Mate' series of remote control panels. I would look to Magnum Energy as a better alternative. You certainly don't need a 2800 watt inverter to satisfy your 120VAC needs. A Magnum MS-2012 will do very nicely!

Midnight Solar (the guys who originally started Outback) make some cool stuff, but a 30 amp controller looks to be too small for the capacity of your panels. I would look to Blue Sky Energy and their 3024i charge controller (40 amps at 12VDC) with their iPN PRO remote, which is also a full function battery monitor system.

If you expect your system to operate seamlessly, you should have a go-to person that is well versed in the interactions of AC and DC systems and one who fully comprehends the effects of various connectors, the effects of voltage drop on specified cable lengths and how these will ultimately affect your system's performance.

I'm done..................


Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
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