Network covert channels are currently typically seen as a security threat which can result in e.g. confidential data leakage or in a hidden data exchange between malicious parties. However, in this paper we want to investigate network covert channels from a less obvious angle i.e. we want to verify whether it is possible to use them as a green networking technique. Our observation is that usually covert channels utilize various redundant "resources" in network protocols e.g. unused/reserved fields that would have been transmitted anyway. Therefore, using such "resources" for legitimate transmissions can increase the total available bandwidth without sending more packets and thus offering potential energy savings. However, it must be noted that embedding and extracting processes related to data hiding consumes energy, too. That is why, in this paper we try to establish whether the potentially saved energy due to covert channels utilization exceeds the effort needed to establish and maintain covert data transmission. For this purpose, a proof-of-concept implementation has been created to experimentally measure the impact of network covert channels on resulting energy consumption. The obtained results show that the approach can be useful mostly under specific circumstances, i.e., when the total energy consumption of the network devices is already relatively high. Furthermore, the impact of different types of network covert channels on the energy consumption is examined to assess their usefulness from the green networking perspective.