Wind turbine

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Highlander,

with your large PV array, I would look very carefully at finding a solution like Tarrel proposed earlier. This must be more cost effective than setting up a wind powered generator.

Even on e-bay there are a good number of high wattage charge controllers capable of 48v input voltages.

If you can devise a method to have these charge controllers swiched into the PV output ahead of the grid converter, you'll be able to charge and top up a 12v battery bank at will, with or without mains power coming into the property.