1.14kw solar for greenhouse fans

steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
Hey everyone. Sorry to make my first post a question, but I really need some help or reassurance.

I run an off grid greenhouse. Currently I am running AC fans off of my honda eu2000 generator. I am switching to solar powered DC fans. I will not need an inverter to start.

So far I bought (4) 285 watt 24 volt panels.
I am powering (6) 30 watt and (4) 90 watt fans.
That is a 1140 watt array to power 540 watts. I included extra to help charge batteries.

Should my battery bank be 24 volt or 48 volt? I do not get many cloudy days so I only need about 12 hours stored. Would about 200 amp hours be sufficient? Which batteries and how many do I need?

Do I need a 30 amp controller? Please suggest one sized for me. I am really not sure about what type I need.

Thanks for any help. I plan to share my troubles and how I corrected them.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,177 admin
    Welcome to the forum SteelHeadGuy.

    Need to understand your loads first. Do you need to run the fans on cloudy days? 9 months a year? How much sun do you get in your location (nearest major city)? etc...

    But as a start: Assuming you need to run the fans 1 day of clouds and 50% maximum discharge (that is pretty hard on batteries--But if you are doing seasonal growing of a few months a year):
    • 540 Watts of fans * 12 hours per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 1 day of storage * 1/0.50 maximum discharge = 318 AH @ 48 volts
    If you only need 1 day of storage, then you could also do a 635 AH @ 24 volts too... (as the battery bank AH rating gets over ~600-800 AH, you are usually better off going to a higher voltage rating).

    And if this is a near full time greenhouse, say >9 months a year and you want to be a bit more conservative in your design, 2 days of storage:
    • 540 Watts of fans * 12 hours per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 2 day of storage * 1/0.50 maximum discharge = 635 AH @ 48 volts
    Note, this is not a small battery bank or a small amount of power usage. If you can find more efficient DC fans/improve natural airflow through natural convection, etc., conservation/reducing power usage will be your friend here.

    Also, if this is a seasonal operation, then the Honda eu2000i may still be your most cost effective power source (plus "cheaper" AC fans).

    Next, how much in the way of solar panels to power this load... We recommend 5% to 13% rate of charge (based on AH rating of battery bank)--And 10%+ rate of charge for full time usage. I.e., the larger the battery bank, the larger solar array you should have.

    If we use the 1 day storage battery bank (the 2 day storage would be 2x larger solar array):
    • 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,198 Watt array minimum
    • 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,395 Watt array nominal
    • 318 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,114 Watt array "cost effective" maximum
    And then there is sizing the array based on power usage and number of hours per day of sunlight.... For much of the US, usually you will get 4.0 hours of sun for 9+ months a year:
    • 540 Watts * 12 hours per day * 1/0.52 off grid power efficiency * 1/4.0 hours of sun minimum =3,115 Watt array minimum
    And here is where you get "hurt"... Off grid power systems give only about 50-60% of the nameplate Solar Panel power Wattage listing.

    Solar panels are, on average, about 81% of name plate, charge controllers are about 95% efficient, flooded cell lead acid batteries can be as low as 80% efficient, AC inverters run around 85% average efficiency, etc.

    So, a lot of this depends on what your exact power needs are... For example, can you cut back on the number of fans on a cloudy day (smaller battery bank, smaller solar array). Is this going to be a 1-2 season operation (more sun) or 3-4 season (lower sun angles, more cloudy weather), etc...

    The above is probably "way over kill" for your needs--The design is based on the assumption you need the fans every day, even when there is no sun (very dark/stormy skies may give you only 5% or so of clear sky power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,653 ✭✭✭✭✭
    The DC voltage your fans operate at, should be the nominal voltage of the battery bank, But if they are 12V, you may as well backup and use cheap AC fans, and an inverter.
    The fans you list, will, over 24 hours, consume (6) 30 watt 4320wh (4) 90 watt 8640wh for a total of 12,960 watt hours (13KWh) Only v 540 watts running, but Wow. That's for sure, 48V territory.
    At 48V, that consumes 270Ah, for a 4 hour solar recharge, you need almost 7,000 nameplate watts of PV. So, you need to re-evaluate your running hours
    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 ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,082 ✭✭✭✭✭
    Why do you need to run fans at night for a greenhouse?
    24vdc fans are abundant and rare at 48vdc, so if you must do this 24vdc is the way. I however believe you could direct drive from the array to the fans with a controller and not use batteries. We do BTW.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 30,177 admin
    For some indoor growing settings, I believe they use fans to mix the air around the plants. So the air circulating around them during the day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
    I am not running the fans at night. The fans operate are variable voltage https://snap-fan.com/ . They are most efficient at 48 volts.
    They are DC fans so there will be no inverter.
    I very rarely get a cloudy day. Will these four panels charge a large enough battery bank for one day? Even if it takes a week to charge?

    I ordered an Outback Flexmax 60 controller. Is this overkill?
  • steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
    How do I direct connect the fans to the panels? Just to the controller?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    How do I direct connect the fans to the panels? Just to the controller?

    No. To the panels themselves, possibly with a Linear Current Booster in between. In this configuration the fans would never run off the batteries. Only when the panels are producing.

    Note that this is not an option if the panel voltage is too high for the fans.
    SMA SB 3000, old BP panels.
  • steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
    Hey everyone sorry to bring up this old post. I ran all of my fans for 6 months this season without a hitch. I connected them straight to the panels and they ran while the sun was up. Surprisingly even while cloudy. This year I am hoping to put in a battery bank. Before I start a new thread I figured I would ask here.

    What is the largest battery bank a 1.14 kw array could charge? I know my array is larger than needed for my fans, so what can I be charging?
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    I am not running the fans at night. The fans operate are variable voltage https://snap-fan.com/ . They are most efficient at 48 volts.
    They are DC fans so there will be no inverter.
    I very rarely get a cloudy day. Will these four panels charge a large enough battery bank for one day? Even if it takes a week to charge?

    I ordered an Outback Flexmax 60 controller. Is this overkill?
    just looked at the spec sheets and i did not see 48 V mentioned, only 35 max...???
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 30,177 admin
    edited March 2016 #11
    Well... Starting with the basic 5% to 13% rate of charge (typical for solar power systems). Assuming a 48 volt battery bank charging at ~59 volts:
    • 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.05 rate of charge = 298 AH @ 48 volt maximum battery bank (weekend/seasonal use)
    • 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.10 rate of charge = 149 AH @ 48 volt nominal (good for daily off grid system usage)
    • 1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.13 rate of charge = 114 AH @ 48 volt minimum battery bank
    Note--If you are sharing the fans as a load with your battery bank--Then your maximum available charging current will be reduced by the current drawn by the fans... Which would decrease the supportable size of the battery bank.

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    BB, the charge rates are all 0.05 above, instead of 0.05, 0.10, 0.13?
  • BB.BB. Super Moderators, Administrators Posts: 30,177 admin
    Thank you South Africa.... I had forgot to edit the actual charge rate after the cut and paste.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
    edited April 2016 #14
    I am planning with a .13 rate of charge for a good healthy charge. 114ah at 48v.

    My 4 panels are 24v, I had them wired in 2 series for 48v. 

    Sorry for the beginner question. But if I have a 24v bank instead of 48v, will this change the amp hours at a .13 rate?
  • BB.BB. Super Moderators, Administrators Posts: 30,177 admin
    Remember--If you have a set of batteries--No matter how you wire the set in series/parallel, the stored energy is the same:

    Say you have 200 AH @ 6 volt batteries (golf cart)--4 of them:
    • 4 in series:
    • 200 AH * 24 volts = 2,400 Watt*Hours of storage

    • 2 in series, two parallel strings:
    • 400 AH * 12 volts = 2,400 WH of storage
    Adding batteries in series, raises voltage. Batteries in parallel, raises Amps (Amp*Hours).

    Same thing for solar panels (series/parallel connections).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • steelheadguysteelheadguy Registered Users Posts: 19 ✭✭
    What I meant was

    1,140 Watt array * 0.77 panel+controller deratings * 1/59 volts charging * 1/0.13 rate of charge = 114 AH @ 48 volt minimum battery bank

    Is it still 114ah at a 24 volt battery bank? Excuse my brain is not working today.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Is it still 114ah at a 24 volt battery bank? Excuse my brain is not working today.
    No, it will be 228 ah at 24 volts.  --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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