solar powered aerobic septic aerator

Poolguy

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!

BB.

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

Cariboocoot

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.

Poolguy

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.

Cariboocoot

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.

Poolguy

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......

Cariboocoot

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.

inetdog

Re: solar powered aerobic septic aerator

Cariboocoot wrote: »

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. :-)

BB.

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

mike95490

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.

DadGramps

Cariboocoot said:

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. " alt="" height="20" />

I don't know why this is so much of a problem. A 12 volt motor is more than able to run an air pump. There are many on the market that do just that 24/7/365. The effluent pump is the sam. 12 Volt pump will create 35 PSI with little or no problem. Many process plants do this for salefty.  A couple of deep cycle batteries such as those for trolling motors and 6 solar panels with the ability to produce 400 watts each should run the system easily. You could run a 12 volt line from a charger that is located inside the nearest building in conduit with a switch that turned on when the batteries got to 33% charge. I'm thinking this should work easily.
Then again I'm trying to figure out why not use 110/120 Volt AC in a conduit to the system? You can run it for 100 yards if the correct breaker and wire size were to be used.
Gramps

NANOcontrol

The vast majority of aerator pumps are vibrator types, no issue with startup or brownout.  Many of the new 150W 12V inverters no longer have a lockup with low voltage, they just stop and then restart once voltage returns.  A battery less system can be built with a buck converter to inverter.  Just remember to add additional caps to input and output of buck converter. to prevent internal caps from eventually blowing.