To set different initial energy to every node

# set initial energy for first node

$ns node-config -initialEnergy 50

set node_(0) [$ns node]

# set initial energy for second node

$ns node-config -initialEnergy 100

set node_(1) [$ns node]

# set initial energy for third node

$ns node-config -initialEnergy 70

set node_(2) [$ns node]

and similarly for more nodes...