.
Differential field scheme is evolved from first two
scheme as it is found that in high insolation period the field
current required is low so differential configuration of DC
motor is simulated and results are really encouraging. For
the simulated prototype the total water collected over the day
through differential field is found to be nearly 5% less than
field current control whereas it was almost 30% less in fixed
current control. Hence it is concluded that variable field
current is best in three scheme but at the same time costly to
implement. So differential compound DC motor is a very
good choice for maximization of utilization factor of solar
array connected to DC motor driven centrifugal pump.