solar powered aerobic septic aerator

PoolguyPoolguy Posts: 10Registered Users
I'm considering powering my aerator air pump on my aerobic septic system via my solar panels already installed in my cabin. I already have plenty of excess capacity to do this, so it's just a matter of hooking it up. My solar panel system is currently only used for 12v lighting throughout the cabin with a stand alone inverter used just as needed in a grid power down situation. The specs. on the pump are 1.6 amps at 71 watts. At 11 cents per Kwh I figure this pump is costing around 6 dollars a month to run 24 hrs a day. Can someone check my calculations?

Anyway, it would save me money so I'm thinking of using a small 100 watt inverter that I already have on hand to power the pump. Sound feasible? Now my overflow pump in the tank is 220v but it runs only a few minutes a month so it will stay grid tied. But that dang noisy aerator pump is buzzing away 24 hrs so I would like to get it off grid if possible.

Any ideas or suggestions would be much appreciated!

Comments

  • BB.BB. Posts: 27,788Super Moderators admin
    Re: solar powered aerobic septic aerator

    0.071 kW * 24 hours per day * 30 days per month * $0.11 per kWH = $5.62 per month

    Does it need to run 24x7 or can it run one hour on and one hour off (etc.)... That will save power and pump life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: solar powered aerobic septic aerator

    Because 71 Watts 24 hours per day is 1704 Watt hours (not including conversion losses and inverter consumption) or a need for at least 284 Amp hours of battery and probably 650 Watts of panel just to run the pump.
  • PoolguyPoolguy Posts: 10Registered Users
    Re: solar powered aerobic septic aerator

    I plugged up a standard 75 watt bulb into the inverter and it pulled 5 amps. That equals 120 amp hours per day. Too much draw that route. I wonder if I have any other options? Maybe a 12v pump? The timer idea looks to be the most feasible.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: solar powered aerobic septic aerator

    Uh, 5 Amps @ 120 VAC is 600 Watts. Times 24 hours is 14,400 Watt hours.
    Divide by 12 Volts from batteries and that's 288 Amp hours, not 120.

    So if that pump draws 71 Watts running on 120 VAC that's (71 * 24) 1704 Watt hours per day. Divide by 12 Volts and you get 142 Amp hours, meaning a minimum battery size of 284 as I said.

    You have to keep the Watts straight in terms of Amps at which Voltage: the Watts are the same but between 120 VAC and 12 VDC you're looking at a 10X factor on the current.
  • PoolguyPoolguy Posts: 10Registered Users
    Re: solar powered aerobic septic aerator

    I measured the amp draw on the charge controller with nothing running except the inverter powering the bulb. It was pulling 5 amps from the battery bank. That's how I got that figure. It's a moot point anyway......
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: solar powered aerobic septic aerator

    Well if the pump only draws 5 Amps @ 12 VDC it isn't 71 Watts, it's more like 60. (Tags on equipment are notoriously inaccurate.)

    Anyway, 5 Amps * 24 hours is 120 Amp hours. Better than 142 but not by much. :blush:
  • inetdoginetdog Posts: 3,121Solar Expert ✭✭✭✭
    Re: solar powered aerobic septic aerator
    Well if the pump only draws 5 Amps @ 12 VDC it isn't 71 Watts, it's more like 60. (Tags on equipment are notoriously inaccurate.)
    But 5 x 13.6 = 68, and if the inverter is 103% efficient there you go. :-)
    SMA SB 3000, old BP panels.
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: solar powered aerobic septic aerator

    Remember that many of the "mid to larger" inverters draw 6-20 watts or more "just turned on". So powering a small 60-70 watt load 24x7 can be a lot worse because of the inverter "tare" losses.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,873Solar Expert ✭✭✭✭
    Re: solar powered aerobic septic aerator

    There is a stress on the motor each time it starts up, and the digester likely wants to see aeration 24/7 or the bio balance may get out of whack and turn anaerobic.

    Leave it grid tie, and just install some Grid Tie solar PV. Trying to run it at night off batteries is crazy talk.
    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 ,

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