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Upgrade Dilemma -- Please Weigh In!

Discussion in 'Off Grid Living' started by openplanet, Apr 26, 2017.


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  1. openplanet

    openplanet Neophyte Monkey

    My girlfriend is moving in, so electrical loads will increase. Getting an apartment sized heat pump dryer, small mini-split heat pump for backup space heating, small microwave, etc. So I need to double my array and battery bank, and am facing a number of decisions that I suspect many others, in one form or another, may be also be facing. So I’d very much like to hear people’s thoughts. I’m totally open to suggestions, advice, and accusations of ignorance or stupidity. After all, that’s why I’m posting!

    Here’s my existing system:

    *Two parallel strings of 3, 295 watt panels in series, for a 1.79 kW array with a Vmp of 135 volts
    *Midnite Classic 200
    *Four Rolls S530 6 volt batteries in a single, 24 volt string for 10kWh of storage (3kWh usable based on a 30% dod)
    *24vdc loads: overhead light fixtures (led bulbs), ceiling fan, pressure pump, SunDanzer ‘fridge.
    *110 vac loads powered by a 2kw Samlex inverter: Staber clothes washer, notebook computers, medium sized flat screen TV, 40 watt receiver, C-pap machine, and a few lamps (led bulbs).
    *Meanwell 24 volt battery charger and Honda 2000eu generator for the relatively few days per year when the battery bank has dropped below 70% soc.
    *I consume an average of 2kWh per day. When it’s sunny the battery bank reaches float by noon. But it’s often...not super sunny.

    As you can see, I’m running a number of critical load on the 24vdc side of the system. I do like the fact that those loads aren’t dependent on the inverter (a.k.a. “a fancy gizmo that can fail”). The few times the battery bank has dropped below what the inverter needs to operate, those critical loads have kept right on cranking. And leaving aside the “All a.c. vs hybrid” debate, I have an investment in 24vdc loads, so even if I decided that all a.c. is the best approach, it’s too late to change.

    I know it makes total sense to double my battery capacity by moving to a single, series, 48 volt string. This would allow me to double the array (just repeating the current panel configuration and putting the two arrays in parallel) and keep my single Classic 200. One downside right off the bat is that I’d be retiring my current bank of Rolls betteries, which are only 2.5 years old and in pretty good shape.

    One approach is pretty straightforward, but expensive:

    *Buy eight new 6 volt batteries to make a 48 volt bank
    *Upgrade to a 48vdc inverter / charger (tempted by the AimsPower’s features and low price, but thinking it may be too good to be true; that is, that at such a low price it can’t possibly approach the reliability of, e.g., a Magnum or a Schneider).
    *Buy a dc-dc buck converter to power the 24vdc loads.

    But here’s the thing…there are other options. I could...

    *Simply replicate the system I have—array, charge controller, and battery bank—and use a great big A-B switch to run the house off one bank or the other. Result—no need to buy a new inverter and dc-dc buck converter, and I only have to buy 4 new 6 volt batteries instead of 8. Yes, I’d have to buy another Classic 200 charge controller...but you have to admit, there’s something about two completely redundant systems that adds a pretty significant degree of fault-tolerance.
    *Buy 4 new 12 volt, 200ah batteries for a 48 volt string of the same kWh capacity of my 400ah 24 volt string, plus a 48 volt inverter/charger. I’d then make use of the 24vdc string by charging it from the 48vdc bank with an MPPT charge controller. In this case I’d run a.c. loads from the 48 volt string, and dc loads from the 24 volt string.
    *Just go ahead an mix the old and new batteries into a 48 volt series string, and accept that the new ones won’t last as they would if the whole string was new.

    So many options...that’s what makes it challenging. But on the positive side, it’s and interesting problem. Ultimately I’ll probably end up going with a new 48 volt bank, 48 volt inverter/charger, and a dc-dc converter for the 24 volt loads. But I suspect people may well have ideas I’ve not yet hit on. So...bring ‘em on. And thank you.
     
  2. oil pan 4

    oil pan 4 Monkey+++

    Get a propane fired dryer if you must have one.
    Don't use the microwave to defrost frozen stuff. It's more or less a complete waste of power.
    Also get a generator if you don't have one.
    Women tend to have a negative impact on off grid solar setups.
     
    Tevin, chelloveck and Sgt Nambu like this.
  3. techsar

    techsar Monkey+++

    Hmmm...wimmens moving in means hair care, i.e. curling irons, long hot showers, lots of lights on (whether they need it or not) for applying make-up....

    Ya know, a good dog would be cheaper...lol:whistle:

    Seriously, is she aware of the solar setup and the fact that there is not unlimited power? If she doesn't, you and her need to have a nice talk before she gets blind sided...and you catch the flak from it.
     
  4. clunker

    clunker Monkey

    I'm with the dog idea. My dog doesn't use any power, obeys commands, and scares away unwanted visitors. lol

    I'm only in the early planning stages for an OG setup, and it looks like you already have roughly double the solar capacity I was planning. Are you in a cool area where a wood stove makes sense. I lived off mine for several years, and it can be your best friend in energy savings.
     
    Sgt Nambu and Gator 45/70 like this.
  5. Tevin

    Tevin Monkey+++

    I totally agree with @techsar

    Adding someone to the household should not have a huge impact on your power consumption. Yes, it will go up somewhat, but it should not create a need to double your capacity unless the person moving in has no sense of what it means to live off the grid and/or your system was too small in the first place. You've already got a substantial system, so I doubt it's the latter.

    Instead of running out and buying a lot of big buck hardware for the sole purpose of accommodating someone else's vanity, have a long talk with her about what it's like to live off grid and how one simply cannot live the way they do on commercial power. Maybe she'll willingly embrace the lifestyle and cheerfully go along, and maybe she won't. But either way, this is something you need to figure out ahead of time.

    Survival Monkey is not a dating/relationship advice website, but I'll go out on a limb and say what you really need to be looking into is your compatibility/shared goals with this person and not the technical aspects of solar power.

    Good luck!
     
    Itchba and chelloveck like this.
  6. oil pan 4

    oil pan 4 Monkey+++

    So what kind of generator you got?
     
  7. Gafarmboy

    Gafarmboy Monkey+++

    Just my opinion here son, but first off go with the dog..They won't demand half your stuff in four years. Secondly, if she knows what you have and is moving in, she is consenting to live "YOUR" life style. So she should be adapting to the live style and you should not being going in debt to rebuild "YOUR" life for her. This rant in not PC, but what the hell. She moves in on your terms or she does not move in...plain and simple. Later on, you can talk about upgrading your system.

    If you can not protect what you own, you do not own it.
     
    Motomom34 and Cruisin Sloth like this.
  8. oil pan 4

    oil pan 4 Monkey+++

    The problem with the eu20 is it only makes 1600w continuously. 2000 is the surge rating. You only get the surge rating if it's not in fuel saver mode. If it's not in fuel saver mode then it's going to use almost as much gas as a direct drive generator.
    That's why I don't own an inverter generator.
     
  9. oil pan 4

    oil pan 4 Monkey+++

    I just got a gas dryer from my local used appliance place for right at $200 with sales tax. It uses 650VA of 120v power and gas obviously.
    My calculations are that it would use 0.5 to 1.5 pounds of propane per load depending on a lot of factors.
    How much does the heat pump dryer cost and how much power does it use?

    From what I can find the heat pump dryer cost around $1,400 new and needs up to 3kwh of 240v power to run.
    Buying one new seems like a really bad idea, running one off grid seems like an even worse idea.
     
    Last edited: Apr 28, 2017
    Cruisin Sloth likes this.
  10. oil pan 4

    oil pan 4 Monkey+++

    Some people can't handle the truth.
     
    Tevin likes this.
  11. Motomom34

    Motomom34 Monkey+++

    Some people read on this site without logging on. The OP maybe re-evaluating the move-in situation after reading one of the posts.
     
    Yard Dart likes this.
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