Aeration pump question

Welcome to the forum Milt.

Here is the basics for a relatively conservative design of an off grid AC power system. I will do this as a 24x7 system that runs year round... It will result in a system that is 2-4x larger than you would expect (or perhaps want). If you have Grid or Genset backup power, or run only 9 months a year, and can turn it off during bad weather--Different assumptions and results. Other options would be to only run the [ump during daylight hours (no battery--Can be 1/4 the cost and almost no maintenance if you can skip the battery bank).

Other options could include Li Ion type battery bank--Smaller but more expensive battery bank---

First, sizing the battery bank, nominally we design for 1-3 days of "no sun"--And generally 2 days of storage and 50% maximum discharge works best/optimally (less maintenance, better battery life for lead acid type batteries)...

• 80 Watt pump * 1/0.85 AC inverter eff * 24 hours per day = 2,259 Watt*Hours per day (measuring actual DC energy usage is useful to confirm)
• 2,259 WH per day * 2 days storage * 1/0.50 maximum discharge * 1/12 volt battery bank = 753 AH @ 12 volt battery bank

Just to give you an idea, a 55 AH @ 12 volt battery run to 50% capacity will run your pump for:

• 55 AH * 12 volts * 0.50 maximum discharge * 1/80 Watts * 0.85 AC inverter eff =  ~2 hours to 50% discharge

So, first issue is a roughly 10=4x larger battery bank if you want to run the pump 24x7 (for various rules of thumb design rules).

Next, two calculations for solar array sizing... First based on battery bank size... Nominally a 5% to 13% rate of charge, with 10% + recommended for full time off grid usage.

• 753 AH * 14.5 volts charging * 1/0.77 panel+charge controller derarings * 0.05 rate of charge = 709 Watt array minimum
• 753 AH * 14.5 volts charging * 1/0.77 panel+charge controller derarings * 0.10 rate of charge = 1,418 Watt array nominal
• 753 AH * 14.5 volts charging * 1/0.77 panel+charge controller derarings * 0.13 rate of charge = 1,843 Watt array "cost effective" maximum

And then there is sizing the array based on where you live and what season(s) you use the system. Say fixed array tilted to latitude for Pittsburgh PA:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Pittsburgh
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 50° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.84	3.45	3.96	4.56	4.60	4.99
Jul	Aug	Sep	Oct	Nov	Dec
5.04	4.85	4.67	4.11	2.77	2.45

So, if this was a year round system with backup power... Pick December as 2.45 hours of sun per day:

• 2,259 WH per day (on battery bus) * 1/0.61 DC power system eff * 1/2.45 hours of sun per day = 1,512 Watt array "break even" December

If this was going to be a full time 12 month system with no AC / Genset backup, I would be suggesting that the "break even" December array  would be 1/0.65 (2,479 Watt array) to 1/0.50 (3,024 Watt array).... But this gives us further issues (need larger MPPT type charge controller, possibly a larger AH battery bank to manage the larger array)...

Obviously, off grid battery based solar power is not cheap... picking an airator pump is no bigger than you need, and the most efficient you can find--Allows you to make the system as small as possible.

Or, if you can pump just during daylight, and to a solar panel -> pump controller -> pump motor allows a much smaller and cheaper system (and no-batteries makes things easier)--Of course, this means no pumping at night/during bad weather from solar.

Your thoughts?

-Bill