Where a Submersible AC Pump is used in conjunction with a windmill, they are most often powered by a diesel or petrol AC Generator. The range of "Gen-Sets" used is 3.5 to 6 kVA. The small size of both the 'subbie' and the 'gen-set' is to match the capacity of this part of the system to the capacity of the windmill. Most often the limiting factor is the bore, rather that the capacity of either the windmill or the 'subbie'.

As a rough rule of thumb the 'gen-set' should be 3 times the rating of the 'subbie'. The most common size 'subbie' is a 1 HP, 30 litre per minute pump.