An apparatus comprising circuitry configured to: determine at least one parameter used to determine an energy cap for a time period for at least one network node within a cluster of at least one network node comprising the at least one network node; determine the energy cap for the time period for the at least one network node within the cluster, based on the at least one parameter; wherein the energy cap for the time period for the at least one network node is determined so that energy consumed by the cluster during a time window comprising multiple time periods does not exceed an energy constraint, the multiple time periods comprising the time period; and transmit the energy cap for the time period to the at least one network node within the cluster at a beginning of the time period.