the equipment used for generating has some amount of weight, which the loco has to haul. besides most of the generating equipment uses dynamo in some form which extracts the energy from moving axles, for which the balance energy has to come from loco.
my only issue here is why mandovi though??? this train travels through tunnels, deep rock cuttings and areas with good forest peneteration. in such cases the sunlight (insolation is the correct word here) isn't sufficient. the choice doesn't make sense.