Each pump manufacturer will have their own pump design based on which they’ll have models in each HP.
Pump stages is nothing but the no of impellers that are required to lift the water from a particular depth. Example, a manufactuer having pump design at 10ft per stage would offer 30 stages to lift water from 300ft depth and the same manufacturer if his design is 30ft per stage would offer 10 stages to lift water from 300ft depth or if its 50ft per stage it would be 6 stages.
Selecting the pump should be based on discharge in liters, which every manufacturer will show in discharge chart/curve & also the type of irrigation method.
If your area experiences low voltage problem, do ask the dealer for LV model of the motor and insist on less no of stages model, as insufficient voltage will not be suffice for all the stages to work.
Coming to your query on Solar;
If effective means performance,
Technically running on solar would longevate motor life as solar system would use VFD that is a slow start mechanism.A good quality solar system would start the motor as early as 7.30Am and run uptill 5.30Pm.If designed properly its a perfect alternative to grid
If effective means commercially,
Unless you face difficulty to get grid supply or have erratic connection solar would not be a viable choice.
Hope this helps!