Nowadays the expansion of cloud computing is only limited to its access to electricity sources while users number increases constantly. My thesis is about reducing the energy consumption of cloud systems by including users into the energy optimization loop. First contribu- tion presented a cloud infrastructure system where users can select an execution mode for the run of their cloud applications. Thus energy- aware users can reduce their footprint on the cloud infrastructure by reducing the size of the virtual resources they are asking for. Second contribution studied the influence of green users on the system energy consumption and compared it with the consumption of more aggressive users in terms of resource utilization. We found that bigger resources are more energy demanding even if they are faster in executing the applications. But, reducing too much the resources size is also not beneficial for the energy consumption. A tradeoff lies in between these two options.