total battery capacity needed.

scottie
scottie Registered Users Posts: 6 ✭✭
I am intending to power a small cabin completely offgrid. I intend to  purchase a sundanzer refridgerator and freezer, both say in spec that they use 800 watts per day. also a 1/3 hp pump, roughly 150 watts of led lighting a laptop and various chargers for cell phones etc. I estimate my daily load at around 2000 watts. I have available to me a 24 volt 2000 watt mono system with a midnite classic controller, all of this seems pretty straight forward however I am getting mixed information on how many amp hours of storage I will need. One more thing is that I think the specs on the sundanzer appliances are at 12 volt, how will this impact my system and do I need to rethink? any help will be appreciated.

Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Running the smaller loads off a small 12v PSW inverter, and the reefer directly on 12v bank would work well. The classic will charge a 12v bank with 24v panels just fine. The panels will potentially produce more than a single classic can use, but not a bad thing for lightly overcast days. Two strings of L16 6v (~700ah@12v) batteries would give you a couple days or so of autonomy.

    The pump could be a problem though. Could it be powered by a generator (which you may need anyway for extended bad weather)? Maybe to gravity and/or pressure tank storage. Depending on the pump, you may be able to run it off 12v, but would need to run it off a much bigger inverter. Would need to know starting and running current specs for the pump.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • scottie
    scottie Registered Users Posts: 6 ✭✭
    I hadn't thought about that, would the 24 volt panels be too much for this purpose and should I just use some of them? Yes I can use a generator for the water pump however I thought if I had the power through the system it would be more convenient. Do you mean 700 ah per string, total of 1400 ah at 12v?
    thanks
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Estragon said:.....Two strings of L16 6v (~700ah@12v) batteries would give you a couple days or so of autonomy.......
    L-16's are about 350ah each, so 2 parallel strings would be about 700ah.
     (wire them on the diagonal :  http://www.smartgauge.co.uk/batt_con.html  )

    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    @scottie

    Solar panels usually don't produce rated power because conditions usually don't match standard test conditions. They can produce more, typically in a clear, cold, high altitude location, but more commonly produce less. This could be because of non-optimal tilt, haze or thin cloud, hot panels, dirt, etc., so having more isn't a bad thing. You could add a second controller if you want to fully use panels, maybe with an opportunity load like water heating.

    Except for the pump, all your loads should run nicely on something like a Morningstar 300w pure sine wave inverter. Using an inverter like this keeps tare load (power used just being on or very lightly loaded ) to a reasonable amount. A larger inverter to run the pump might take 30w or so in tare losses, which could add nearly 50% to your daily power use. The big inverter may have a search mode to reduce tare losses, but running the small loads will keep it out of search. One solution would be to get both a large and small inverter, and use the big one just for the pump. 1/3hp isn't a huge pump, so likely can be done on a 12v system. Would need specs though.

    2000w daily use is around 160ah. 2 days would be 320ah which would be about 50% state of charge on a 700ah bank, which is about as low as you want to take a lead acid deep cycle battery. L16s are pretty common and can make a 700ah 12v bank without using lots of parallel strings.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    scottie said:
    I am intending to power a small cabin completely offgrid. I intend to  purchase a sundanzer refridgerator and freezer, both say in spec that they use 800 watts per day. also a 1/3 hp pump, roughly 150 watts of led lighting a laptop and various chargers for cell phones etc. I estimate my daily load at around 2000 watts. I have available to me a 24 volt 2000 watt mono system with a midnite classic controller, all of this seems pretty straight forward however I am getting mixed information on how many amp hours of storage I will need. One more thing is that I think the specs on the sundanzer appliances are at 12 volt, how will this impact my system and do I need to rethink? any help will be appreciated.
    I think all these Sundanzer fridge and freezers will run off 12 or 24 volts. Typically freezers use less electric as they have thicker insulation and are opened less. Might check your specs.

    Look at what else you might need to run. Suspect you are underestimating your loads. As someone has said, pump to a gravity fed system might be easier on your electric requirements.

    2000 watt array would handle about 500 amp hour 24 volt system, in daily use, maximum, provided you see enough sunlight. Check your solar isolation.

    As to how it will impact your system, you will want the fridge and freezer near the battery bank, running DC electric long distances comes at a cost of loss in wiring or needing to run very thick wires.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • scottie
    scottie Registered Users Posts: 6 ✭✭
    Thanks for the help, I am learning a lot and I appreciate the input. I have talked to sundanzer and they told me that the fridge would use 800 watts a day at 90 degrees and less than 300 for the freezer so my demand will be smaller than anticipated. they told me that my midnight controller with only 1000 watts of panels would be more than sufficient if I had 400 amp hours of storage. I have also found out that there is a device that can monitor the level of my battery bank and automatically start my small diesel generator when they reach a preset level. anyone familiar? brands? prices? my genset has a two wire start. also I have determined that I can use a water holding tank and fill it when needed with my generator.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I'm not a fan of auto gen start myself. Lots of things to go wrong potentially with nobody around to intervene. That said, people do use them and seem ok with it.

    If you're running 1100wh/day, 1000w panel and 400ah sounds ok. What about your lighting and other loads though?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter