Help With New System

MelLandryMelLandry Registered Users Posts: 5
Hello. I'll start by thanking everyone for the help you've already provided. I've been scanning the forum and have learned a lot. Your discussions have helped get me this far. For instance, you've talked me out of running many things off of 12vdc as I had initially planned.

I'll soon begin construction of a floating off-grid cabin. The cabin will be approximately 500 square feet of living area and will be studio-style with lofts (so no walls/partitions except for the bathroom. It will be located in Louisiana and will be utilized mainly on the weekends and perhaps for a week at a time a couple times a year.

My #1 goal is to minimize maintenance and maximize ease of use as much as is practical so that I can enjoy all the other great things that come with being out in the wilds. My #2 goal is to keep costs reasonable. I realize these two goals sometimes (often) conflict.

Because of my use patterns and anticipated load, I've concluded that a system mainly powered by a gas generator is the best approach. However, I'd like to utilize a small battery bank so that I don't have to run the generator during times of light loads. Also, I understand that battery bank can help mitigate short spike loads, thus reducing the size of the generator I might need.

I've included a picture of my wattage and amp hours calculation. Some 12vdc items remain from my previous intentions, but those will be converted to 120vac as I move forward. The changes are likely insignificant enough not to drastically impact that calculations. I have some things in there that will likely get used VERY INFREQUENTLY. For instance, that microwave and that induction plate will very seldom get used (I'll have propane for cooking under most circumstances). What remains are relatively light loads with the exception of the window unit AC and the refrigerator. My plan is to never use the AC or refrigerator on battery power. The batteries will be used to run lights, the TV, and the on-demand water pump when the generator is not running.

Here is my plan:

Generator: Champion Model #46539 3500W/4000W GENERATOR WIRELESS REMOTE START (or the cabela's equivalent Model #46578 )
Batteries: Two Full River DC400-6 batteries
Inverter: Samlex Model: EVO-2212 EVOLUTION Series Inverter/Charger (+ EVO-RC remote)

I recognize that the selections here are not the same names that I'm typically seeing (i.e. a 24 volt system with an Outback inverter with Surrette batteries). I've done some research on features and prices and the combination of the two have led me here. I think I've set myself to grow a little over time by adding solar, expanding the battery bank, and setting up the system to auto-start.

On auto-start... is it worth the trouble? The Samlex remote manual states as one of the parameters: "When the battery voltage is lower than “LOW VOLT ALARM”, the Status Relay turns ON. When the battery voltage is higher than the “RESET VOLTAGE”, the Status Relay turns OFF. This function may be used for Generator Auto Start/Stop in conjunction with optional external Generator Auto Stop/Start Module." It seems like with this remote/generator combination, I wouldn't be far from being able to set it up for auto-start. Is this something I could/should easily do?

I also have a set of these panels laying around:

I don't have the charge controller, so I'd have to buy a new one. Would they do any service to keeping a maintenance charge on the batteries when I'm not there? Or should I just throw them in the trash pile?

Any critical issues you see? Any experience using any of these products or a combination of them?

Thanks in advance for all of your help!


Mel Attachment not found.


  • BB.BB. Super Moderators, Administrators Posts: 31,886 admin
    Welcome to the forum Mel.

    Looks like you have done a good job looking at your loads... You are looking at a 380 AH @ 12 volt battery bank (I think). That is a pretty good sized battery bank for a 12 volt system... 12 volt system wiring can only have around a 0.5 volt drop from battery bank to AC inverter... And you should have something like a 0.05 to 0.10 volt drop from charge controller to battery bank (for accurate/fast battery charging).

    That means relatively short/heavy cables. I see some 12 volt loads too. I would be tempted to use a MorningStar 300 Watt 12 VDC TSW (true sine wave) AC inverter for your system--And change the LED/phone charger/etc. other small loads to AC instead. Wiring will be much easier.

    A 2.2 kWatt 12 volt inverter is a lot of current... I would suggest around 1,200 to possibly 1,800 Watt or so maximum for 12 AC power (to keep wiring size "reasonable"). For example, a 2.2 kWatt inverter would need:
    • 2,200 Watts * 1/0.85 inverter eff * 1/10.5 volts battery cutoff * 1.25 NEC wiring/breaker derating = ~308 Amp rated 12 volt branch circuit.
    A good reason to look at a 24 volt battery bank--If you really want to run those loads--Otherwise stick with Propane/AC generator if you can.

    Power usage--For AC power, you should use a 1/0.85 typical AC inverter efficiency fudge factor for your battery/wiring sizing (regarding AC circuits). Just for sake of discussion, take your 155 AH @ 12 volts with 1/0.85 inverter eff (I think understand your chart--I did not double check the numbers):
    • 155 AH * 1/0.85 inverter eff = 182 AH per day (assuming all loads run from AC inverter)
    • 155 AH * 12 VDC = 1,860 Watt*Hours of loads (assume these are all 120 VAC loads to keep math simple and conservative)
    Looking at battery bank, normally I would suggest around 1-3 days of storage and a maximum of 50% maximum battery discharge for normal use--2 days of storage usually works out pretty well:
    • 1,860 Watt*Hours per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 maximum discharge 1/12 volt battery bank = 720 AH @ 12 volt battery bank
    So--I am not sure if your 155 AH was a "worse case" or your average daily loads. Getting to ~800 AH battery bank would usually be a good idea to move from 12 volt to a 24 volt battery bank.

    Next, sizing your solar array... I would not bother with the SunForce panels. They usually do not work very well for a full time off grid/permanent solar install. And, anyway, those panels are too small your your needs.

    When sizing a battery bank, I suggest doing two sets of calculations. First based on 5% to 13%+ rate of charge -- For battery health the typical recommendations would be:
    • 729 AH * 14.5 volts charging * 1/0.77 panel+solar charger deratings * 0.05 rate of charge = 686 Watt array minimum (weekend/seasonal use)
    • 729 AH * 14.5 volts charging * 1/0.77 panel+solar charger deratings * 0.10 rate of charge = 1,373 Watt array nominal (full time off grid living)
    • 729 AH * 14.5 volts charging * 1/0.77 panel+solar charger deratings * 0.13 rate of charge = 1,785 Watt array "cost effective" maximum
    Of course, if you only need the 380 AH @ 12 volt battery bank, the above array sizing would be about 1/2 as large.

    And then sizing the array to the amount of sun you will receive (and for the seasons when the cabin would be used). Using PV Watts, fixed array, tilted to latitude (31 degrees), Baton Rouge, we get:

    Solar Radiation
    (kWh/m 2/day)














    If you are there full time, plan on running ~9 months of year from solar, and the other 3 months use the genset for bad weather.. Gives us 4.37 Hour of noon time equivalent sun per day (November):

    1,860 WH per day * 1/0.52 end to end system eff * 1/4.37 hours of sun per day (Nov "break even" month) = 819 Watt solar array minimum

    Again--Just demonstrating the math and "my assumptions"--Yours will probably be different (smaller battery bank, perhaps not all loads every day, use genset a bit more because of A/C and refrigerator loads, etc.).

    Personally, I would avoid autostart for genset unless you really need to to be automatic (run when you are not there, spouse/kids). Automation can get pretty complex pretty quickly. And things go wrong all the time (no gasoline, genset does not start because of no fuel/low oil/wet wiring, etc.).

    Anyway--I will stop here. My first suggestion is conservation and choosing the most energy efficient loads you can find. Generally, it is cheaper to conserve than to generate the power.

    I do like that you have solar power loads (in general, small low power devices) and use the genset for large loads... A small off grid power system is around 1,000 WH per day. A system large enough to run a refrigerator + rest of home is somewhere around 3.3 kWH per day--And not "cheap".

    You are sort of inbetween. A bit larger system, and you could run a refrigerator full time (or at least ~9 months of year) plus lighting, water pump, electronics. Things that run 12-24 hours per day (like computer, networking, sat box, etc.)--Look at reducing those loads. Your numbers are a bit on the high side compared to what may be available (if those devices will meet your needs).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MelLandryMelLandry Registered Users Posts: 5
    WOW Bill! Thank you very much. I feel like I should have paid for that kind of advice and detail!

    The 12v loads I have in my spreadsheet will likely be replaced with AC versions, so the mixed 12vdc / 120vac issues can be put to rest.

    The numbers I used for my load calculations are what I'd expect on a typical day... perhaps slightly conservative (I could imagine using the lighting less). So with that as a starting point for your calculations, I think I'm in really great shape.

    You've almost got me talked into making the jump to a 24v system. If I stuck with the Samlex, the 24v 2.2kw EVO-2224 is the same price as the 2212 12v inverter, so it doesn't seem anything would change in the calculations except a reduction in the necessary wire gauge.

    Again, thank you so much for your help. As a novice, I'm able to grasp many of the concepts/calculations in isolation, but I've struggled to string them all together as you have. This is a great help and will be a highly useful reference as I move forward.

  • BB.BB. Super Moderators, Administrators Posts: 31,886 admin
    You are very welcome Mel.

    I recommend that you do your paper design(s) first before you purchase any (more) hardware. There are a lot of details to work out first and buying stuff on sale/Craig's list before you have your design can end up costing you extra time and money to make everything fit.

    Also, when you get to a larger system, many folks will let the AC inverter run 24x7... And larger inverters you will need to take into account their "tare" load (power used just because the inverter is turned on). For the Samlex series:
    12v: Normal Mode: 30W; Power Save Mode: <8W
    24v: Normal Mode: 25W; Power Save Mode: <8W
    • 25 watts * 24 hours per day * 1/0.77 panel+controller eff * 1/0.80 battery eff * 1/4.37 hours of sun per day = 223 Watts of "extra panels" to run inverter 24 hours per day (rounding up)
    Regarding the genset... Champions seem to be a good quality generator. Please note the fuel consumption. A 3.5 kWatt genset will around 0.5 gallons of gasoline per hour at full load, and something like 0.25 GPH at 1/2 load or less.

    Look at your loads and planned run time. If you need the power and can run the genset at ~50% or greater load--The fuel consumption, while it "hurts", is at least relatively cost efficient. However, if if your "average" generator loads are 25% or less, the fuel efficency (kWH per gallon) will be poor as the fuel flow for a gasoline fixed RPM genset will usually stay near 50% rated fuel flow even down towards 0% rated load.
    Up to 12 hour run time at 50% load
    3.8 gallon fuel tank
    • 3.8 gallons / 12 hour run time @ 50% load = 0.32 gallons per hour
    If you run the genset ~12 hours per day--That is almost 4 gallons of fuel per day
    • 12 hours * 3,500 Watts * 0.50 load * 1/3.8 gallons = 5,526 Watt*hours / Gallon = 5.5 kWH per gallon of fuel
    • (1 gallon fuel * $3.30 per gallon -- fuel is expensive in California) / 5.5 kWH per gallon) = $0.60 per kWH
    Run at 1/4 load, and you can easily see $1.20 per kWH (assuming fuel GPH does not drop much at lower usage).

    Note that these type of gensets are not quiet. Running next to the living space without sound insulation (and good ventilation) can be uncomfortable. And dangerous if you have a fuel spill/fire/fumes in bilge/etc. (will the genset be "floating" with the cabin, or on shore/separate structure?).

    In general, I would be very careful with the entire design/build. Use circuit breakers/fuses where appropriate, Good ventilation and fuel storage for genset. If you have a bilge, you will need forced air ventilation & flammable fume detector for gasoline/propane fumes.

    Let us know how the whole project works out for you... It is always nice to see working projects and any issues you may have had.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MelLandryMelLandry Registered Users Posts: 5
    Thanks for the continued input Bill.

    Ensuring the generator is experiencing as much load as is reasonable (to maximize energy/gal) was the impetus for deciding to pursue a battery bank rather than just running off the generator full-time. So it seems we're on the same page. Practically speaking, the generator should run at night to power the AC which combined with the load from the battery charger should keep the load up. Then I can use the stored power in the batteries to operate the less demanding items in the morning and throughout the day while the generator is off.

    That use pattern is why I initially plan to start with the genset and the batteries and expand to solar later.

    As for the noise and safety of the generator... The cabin will float on foam billets (so there is no bilge). The generator will be placed outside of the living area on the porch and the plan is to construct a sound-insulating enclosure (with fans) to reduce and direct noise away from the living area (as well as exhaust). There will still be some noise of course and some vibration, but the time I've spent on similar cabins has shown that these things don't seem to bother me. In the future, I would have the option to move the generator to an isolated platform, but every decision must also account for security...

    I fully intend to sketch it all out as I proceed and I'll be back here soliciting review. I'm a big believer in "draw twice, cut once", to put a new twist on it. The entire cabin has been fully designed down to the studs in SketchUp. Now is the time to start designing the mechanical and electrical, which is why I've found myself here. Luckily I haven't purchased any of these components just yet, so I've got plenty time to make mistakes on paper. Hopefully I can start construction in the next few months with a goal to be wife-ready by the end of the year.

    Thanks so much for all of your help. You've already saved me much frustration and money! I'll be back with update as the design progresses.


  • BB.BB. Super Moderators, Administrators Posts: 31,886 admin
    Look at mini-split A/C systems--They can be very efficient--And if you get the heat pump version, can provide pretty cost effective heating down to near freezing.

    Generator wise--You might want to look at the Honda eu family. If you can get away with an eu2000i to run a (relatively) small A/C system--The gensets are very quiet and relatively fuel efficient down towards 400 watts of load (one mini-split, no longer available, would run down towards 300 watts on low).

    Of course, watch out for carbon monoxide fumes.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MelLandryMelLandry Registered Users Posts: 5

    I looked at mini-splits but couldn't find many options in 120v. If there is a choice model that most folks are picking (smallest, most energy efficient), please pass it on.

    This is the window unit I was looking at:

    The plan for heat was to use a propane wall-mount heater. I'll have a couple propane/CO detectors installed for safety. Heat isn't in high demand down here... it's the other end of the thermometer that tends to cause discomfort. So I won't need to use the propane heater too often. I am also planning to spray-foam insulation the cabin, so a little climate control will hopefully go a long way.

    I shied away away from the Honda EU series because the 2000 didn't seem sufficient enough for the combined use/charge load of the system (since I plan on focusing on generator first and solar later), and larger than the 2000, they got pretty expensive. The greatest advantage seemed to be the inverter capabilities, but since I have an inverter in my system it didn't seem necessary.

  • BB.BB. Super Moderators, Administrators Posts: 31,886 admin
    Sanyo made a pretty nice mini-split @ 120 VAC--But when purchased by Panasonic, they killed that model... And now native 120 VAC mini-splits seem to be difficult to find.

    You can plug this search string into Google and find threads about the Sanyo--And possible 120 VAC options:
    • sanyo mini split ac
    I don't have/use AC here--So I really do not have any good options to suggest--Hopefully some other folks can chime in here.

    I believe the 120:240 VAC autotransformer from Outback will not work correctly on the Honda eu2000i (to much starting current required by the transformer when first turned on--eu2000i cannot handle the surge current).

    Latest mini-split thread (no 120 VAC units in it):

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.