Small Off-Grid System w/MSW Inverter

SolManSolMan Posts: 15Registered Users
Hello everyone. I've been a fly on the wall for a while and learned a lot here, but I still have many questions about everything.
I am currently faced with designing a small off-grid system for a client who wants to run a water pump, lights, and a TV in a hunting cabin that will be used rarely. There is a generator available, but client does not want to run it at night...hence the desire for some battery back-up and solar to charge it while no one is there.
There are other loads as well, but presumably could be run off gen during day to limit solar cost.
I am looking at a Xantrex DR1524, (4) L-16's, and (4) Sharp ND-130UJF modules after figuring avg amp-hours/day in the 100-120 range.
We have 4 hours avg winter-time peak sun (5.8 annual avg) which is when the cabin would be used (Fall/Spring).
I'm not sure about the DR powering a TV, but this is a necessary load.



  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Small Off-Grid System w/MSW Inverter

    You need a lot more specifics about the proposed loads.
    For instance "water pump". If this is a standard, AC-induction motor pump as used in most well applications (1/3 HP to 3/4 HP) it isn't going to work off a MSW inverter.
    Then you need to know things like peak current draw of any one given device, so that the inverter won't "kick out" when it turns on. Then you need to know the over-all wattage/time load for everything, as in "1.4 kWhrs/day". You're going to have to replace all those watt-hours in whatever charging window is available. That brings up the question of panel orientation. Is it possible to aim the array to solar south? If so, how many hours of direct sunlight will they get?
    The other thing that nobody ever thinks about until after is: once he's got electric for that he'll decide a toaster (or something) would be nice - and need more power. We all do!
    Over-all, the panels you mention should be able to charge the (good choice L-16) batteries okay. But you'll also need a MPPT charge controller for optimum performance (some sort of CC is necessary no matter what). I think that Xantrex DR1524 is discontinued, so it may not be the best choice. Check out some pricing on True Sine Wave inverters and see if it isn't a good idea to go the extra mile, so to speak.
  • nigtomdawnigtomdaw Posts: 705Solar Expert
    Re: Small Off-Grid System w/MSW Inverter

    The DR range is being discontinued but has been replaced by the new Trace TR series model for model still MSW but with PFC (power factor corrected charging) , simply put more efficient at using generator power to charge batteries plus a digital display . A TV should be no problem on MSW maybe a little noise distortion ocassionally. MSW causes many electrical items to run hotter and thus have a reduced life span some items like power tool chargers and security lights will last a few seconds. . Take a look also at Magnum energy they also do PFC MSW inverter chargers.

    Ive used MSW units all DR units and found them extremely reliable and simple to set up and use .U will get those that tell you to stretch to a Pure Sinewave unit but price is often a factor and amount of use also, I have three friends using DR units all know there limitations on what will fry and die and what is OK.They get by with charging mobile phones and power tools when the genny is running using the sinewave from that !

    Make sure you use a BTS (battery Temp Sensor) to provide accurate charging in the various seasons .

    HTH Nigel
  • mike95490mike95490 Posts: 7,562Solar Expert ✭✭✭✭
    Re: Small Off-Grid System w/MSW Inverter
    SolMan wrote: »
    (4) Sharp ND-130UJF modules after figuring avg amp-hours/day in the 100-120 range.
    We have 4 hours avg winter-time peak sun (5.8 annual avg) which is when the cabin would be used (Fall/Spring).

    120AH/day draw (I'll assume this is 12V battery amps - not 120VAC amps)
    120AH x12V = 1440WH daily draw.

    4.8Hr sun 130 x 4= 520W 520W x .8 derate = 416W x 4.8H = 2000WH @ 12V
    2000WH x .8 battery recharge losses = 1600 WH possible

    Inverter losses (20%) are not factored in, and would make this a bit worse.

    If you never have clouds, this might work, if you use a MPPT controller to squeak out every possible watt. This would top off the batterys by Tues PM, is used on weekends, and a bit extra power was drawn.

    Running a small genset in AM for 0.5 hr to both Bulk Charge and run a coffee pot, would nearly assure success.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Small Off-Grid System w/MSW Inverter

    Just FYI,

    We live in a small, 700 sq ft cabin. We use between 400-600 wh/day. This is for lighting, radio, water pumping (24vdc submersible shurflo) fridge ignitor, (l/p fridge) fridge condenser fan, ceiling paddle fan, lap top, satellite modem and router, 3 watt cell phone. We're pretty conservative with our usage. We keep 4 t-105's charged with ~200 watts of panel and the Bluesky 2512 mppt controller. We only have to run the generator if we go 3-4 days without sun. 3 days draws us down to about 80%soc.

    Our use would be pretty similar,,,but add in a CRT TV and you probably jump it a bit,,,if you have a small lcd it would probably equal our laptop use. If I had to do it over,, I would add twice as many panels and go back to 4 l-16 batteries. As with anything, the loads grow with time.

    As Mike suggests, sizing the PV for the idle time, use the generator for "fill power" and use the battery at night. You could make the argument that if you are only using the system on weekends you could live with a deeper level of discharge, say 50%. You might give up some battery life, but the trade off of not buying too much capacity that will only be used a few days a week might make sense.

    T-105's are cheap enough that killing a set every few years may not be that big a deal to some people. Personally, I like to get 10 years out of a set. My original t-105's are still going at their 11th year. My l-16's are in their 12th, although I have only 4 of the original 6 left. (I use these two strings on a couple of small seasonal buildings,,keeping them up over the winter with a couple of panels).

  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Small Off-Grid System w/MSW Inverter

    Just a quick observation: Looks like you're talking about a 24V system? My main question would be is there a water tank that could hold the water, only operating the water pump while the generator is running? I suppose this also means that we need to know how big the genny is and a bit more about the pump. As has been said more info on the loads would help a lot. The big thing to remember about a battery based system is that it's much more complex than a simple amps out/amps in comparison. How often will it be in use in the winter, how long between visits, etc....
    I wish I could find it now but I think that Crewzer once posted a really helpful link here that spelled it out as far as charging batteries, but essentially the idea is that with the last couple of hours needing to do the absorb stage, you'll need to do the vast majority of the charging before that point in time (still leaving a good couple of hours of high sunlight to finish the absorb stage). Anyways... give us some more to go on ...
  • BB.BB. Posts: 27,214Super Moderators admin
    Re: Small Off-Grid System w/MSW Inverter

    By the way, Solman has not been here since December 3rd (2008)--so probably leave the thread rest unless/until "he" returns.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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