In this paper, authors discuss the energy consumption for 1 bit transmission as a function of spectral efficiency (SE, bps/Hz), aggregated traffic amount (C, bps), and overall transmission distance (LP2P, km) in wavelength division multiplexing (WDM) systems with optical add-drop multiplexer/ optical cross-connect (OADM/OXC) nodes. It is found out that 100G dual polarization quadrature phase-shift keying (DP-QPSK) is the best solutions among two other considered – 10G non-return-to-zero on-off keying (NRZ-OOK) and 40G NRZ differential phase-shift keying (NRZ-DPSK) – in terms of both energy consumption per bit and spectral efficiency. Finally and foremost, it is estimated that for the WDM channels added though the OADM/OXC node, energy consumption per 1 transmitted bit could growth more than two times as compared to systems without OADM/OXC (point-to-point configuration) or for the channels dropped in the OADM/OXC node.