Off grid backyard trailer solar

If I have 4 solar panels of 305 watts per panel, should those panels be wired in one string of 4 panels, or two strings of 2 panels in parallel? Would a charge controller be able to the combined voltage of 32.7 Vmp per panel (130.8 total?)

Thanks for the input Scooby Mike. Where would I find the Classic sizing tool?

I expect that a daily refrigerator load of  approximately 300 kilowatt hours would be my constant load per day in the winter. Add another 500 watt hours per day for led lights and charging cell phone and laptops and I think I am at about 1 kilowatt hour per day.

The summer a/c demand I think will be about 1.5 kilowatt hours overnight, supplemented by the Honda generator.

My only reason for considering a 24 volt system was for presumed efficiency when compared to a 12 volt system. But I have not yet seen any explanation of that concept, so I don't know if that is a significant consideration. At some point, 12 volt appliances will be in use, even in the current trailer configuration. I presume that there would be some power consumed when converting from 24 volt to 12 volt, but I don't know the magnitude of that loss.

I would still use a/c in a conversion van, but more generator supplementation would be needed due to one less solar panel in the system. At about 420 watt hour consumption for the a/c, it seems to me that the Honda 2200i with 1800 watts normal would run in eco mode with that load. Direct  connection of the a/c unit to the generator overnight would eliminate any stress on the solar system and battery/inverter. With a low power draw refrigeration system I would think any surplus daytime solar input beyond daytime a/c consumption would satisfy any night time refrigeration demand. A freezer only setup would mean that the freezer could be shut off overnight and maintain frozen food until the following day. 

What type of DC refrigerator do you have?

I think daily cumulative loads of 1200 watts or less are possible, with the exception of the a/c at maximum draw of 420 watts for approximately 4 hours overnight (during the summer only.) Assuming a battery bank of sufficient capacity to accommodate that increased load overnight (with early evening and/or early morning generator supplementary power input when necessary), would a 12 volt system be appropriate for that total demand of ~ 3000 watt hours per day?  I am assuming that 1220 nominal watts of solar panels will support the a/c consumption of 420 watts per hour during peak sunlight hours during the summer.  I am also assuming a daily generator input of 3000 -4000 watts to support the a/c in non peak sun hours in the daytime and evening hours.  (The Honda 2200i generator operates in normal mode at 1800 watts, and in eco mode of 1/4 output, or at 450 watts, and the a/c operates on high cool at about 420 watts.)

I see a benefit in have a 12 volt system which can charge cell phones and laptops directly from the 12 volt battery bank with a standard cigarette lighter socket without taxing the inverter.  A 12 volt power roof vent with low amp draw would be a suitable feature for transitional seasons and general humidity control.

Thanks for all of the information.  I am staying with the roof footprint of the trailer to determine the number of solar panels.  Any ground mount or roof mount options on permanent structures requires extensive municipal design approval and permitting and $$$.  I need for this trailer installation to be transportable and to have realistic potential for ultimate relocation to a conversion van without extensive new equipment purchases.

I have read elsewhere, and I believe, that your first off grid battery bank should be comprised of inexpensive batteries because you are likely to make a big mistake somewhere along the way and ruin your batteries.  LiFePo batteries sound nice, but I think their longevity could be easily comprised in inexperienced hands like mine.   I am willing to spend the extra $$ for AGM batteries since I have read that they have a operate at 95% efficiency as compared to the 70% efficiency of FLA batteries.  This indicates that about 25% less AGM batteries could used in place of FLA batteries for an equivalent useable AH capacity.  The possible faster charge rate (which still seems debatable based on what I have read) might result in less generator fuel being consumed when compared to charging FLA batteries. 

Once installed, there will likely be times when I am not able to attend to this system on a daily basis, so whatever system I have needs to be safe and robust enough to independently operate without my daily oversight.  We had temperatures down in the 30s (F) last night and when it is windy with very little humidity the "feels like" temperature is a lot lower.  Winter temperatures at night are below freezing on many days.  Conversely, we have a summer monsoon season (roughly June through September) where temperatures can reach 115 degrees with very high humidity.  This is the season when Tucson receives most of its average 11 inches of rainfall per year. My understanding of lithium batteries is that they should not be discharged at extreme temperatures, and I will likely not be around at times to monitor their state of health.  I know that electrical devices can be configured to stop discharge outside of certain temperature parameters, but that places a $4K-$6K battery investment in the hands of a device which can fail in my absence.  I am not impressed with the 2 year warranty on inverter/chargers. I would think that such expensive devices would be reliable enough to at least approach the powertrain  warranty on new cars (which are now rolling computers.)

With regard to measuring my total power consumption with a Kill-A-Watt meter, I have been doing that for the past 3 weeks and have determined that 1.5 to 2.0 killowatt hours during the winter is what my consumption would be.  This is based on the current 1.5 kw hours per day consumption of my energy hog 10 cu. ft. frostless refrigerator.  If the 3.5 cu.ft. chest freezer or chest freezer to refrigerator conversion was tested, and confirmed to be 300 watt hours per day, I think 1 killowatt hour per day in the winter would be the accurate estimate.  I currently fire up a small 2.5 gallon electric water heater in the trailer which consumes 1400 watt hours for 15 minutes, so it consumes 350 watt hours total.  No surge start up watts there - totally a resistive load - so although it would tax the battery bank for 15 minutes and does represent a large percentage of the daily winter load,  running the generator for 15 minutes would not cost much in fuel and be better than dealing with the additional fuel source that a propane heater would require.  An electric water heater is simple and requires no maintenance, as long as soft water supplies it, and I do have a water softener installed in the trailer. I have not had good experience with rv style gas water heaters.  I find them to be way more trouble than they are worth, as long as a tiny 2.5 gallon water heater will do the job. 

I started up the 450 watt a/c a few days ago and I saw no significant surge from this 5000 BTU Frigidaire model. Even when turned to high cool on startup, it runs only in fan mode for about 90 seconds, then ramps up to 400-420 watts.  I have read elsewhere on RV fourms that this model has a built in soft start mode, but I have no confirmation on that.  I have seen videos of this a/c unit starting up and running on eco mode, but I have no first hand verification of that.  I would expect to run the a/c on the inverter, which I assume could hand a small surge load, but would run the a/c straight off the generator if necessary.  This a/c has no digital controls - just rotary dials and numbers to set the thermostat, which is why I installed a 6000 btu a/c unit with remote a few years ago.  That unit also has a "soft start" feature but consumes power in the 580-640 watt hour range.  I can give up the convenience of digital temperature readout and remote control for the purpose of energy conservation.  However, since the 6000 btu a/c can cool the trailer down in a hurry, it might be more economical to run the 6000 btu unit, especially if I install a partition wall in the trailer to reduce the cu. ft. of room space by about 1/2 (although this would also cause more short cycling and less dehumidification in the monsoon season.)

Yes, I have used them. In my case, they a lasted about 6 months to a year then broke- not worth fixing. Those are ok in warm weather. In cold weather they only raise ambient water temperature by a specific amount, and the resulting water may be warm but not hot. Also, they use propane, requiring me to stock another fuel, and they should not be used indoors.

I set the 2.5 gallon electric water heater to my ideal temperature (about 114 degrees F) and did not waste any water while trying to get the correct temperature. My experiment shows that 2.5 gallons will provide for a  navy shower with enough hot water leftover to wash dishes. I don't think 15 minutes of Honda generator full run time at a nominal 1800 watt level (with 400 watts of spare power to add to the battery bank) would be any more expensive than running propane heater.

I know you have a good idea and every RVer I know uses one, but I think I will be the nonconformist on this one.