Somewhere on the pump/motor is a tag or label the should show voltage and amperage or voltage and wattage. You may allready know the voltage if it just plugs up to a 120 volt receptacle. If the pump/motor is inaccessible and/or its not "plugged up" instead its "hard wired"as it may be if its 240 volt, you may need to get a multimeter with a clamp on amp meter. However its done there are three things that must be known; 1 - voltage, 2 - amperage or wattage, 3 - runtime over the longest period of time of a blackout anticipated. Is it a residential sewage pumping station or more like a basement sump pump? Sometimes the pumping stations will have two different circuits. One for the pump/motor and the other for the control/alarm (in case the pump fails and the liquid level gets too high.
I will give you an example of the math.
120 vac 8 amps = 960 watts X 6 hours of runtime in a 24 our period = 5,760 watt hours or 5.76 kilowatt hours.
5,760 watt hours / 24 vdc nominal = 240 amphours.
240 amphours X 5 = 1200 amphours battery bank.
That multiple of 5 would keep the battery bank in its top 20% of charge which would increase its overall life span and help it to recovery it charge faster the next sunny and/or windy day.
The PV array.
240 amp hours X 24 vdc nominal = 5,760 watt hours.
5,760 watt hours / the number of hours of full rated charge from a PV module ?4 = 1,440 watt PV array at 24 volts nominal.
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/Go here and select; average, annual, and flat plate tilted south at latitude. Find your area on the map and it will give you an overall idea of how many hours of equivalent full rated charge you can anticipate.
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