I do like the idea of setting up the pumps and lights to run full time from an alternate supply.
If you are going to go to the additional expence you might as well be getting the most out of it all the time instead of the occasionl power outage.
Instead of stepping up the voltage from your storage batteries, through an inverter, what about running the lights off 12 volts. RV camper supply stores may be able to help out with the lighting. Farm supply stores have 12v fuel/water pumps that may do the trick. Use the electric grid as back up for when the wind dies down for 3-4 days or the sun stays behind the clouds.
Your alternate supply ( excluding batteries ) will probably have to be able to carry 2-3x the load required under normal operation. The extra power to be used for maintaining the system for nighttime operation, if solar, and to recharge the batteries for/after 'short days'.
Somebodies sig line says "Fate favors the prepared" , I tend to agree.