Energy consumption in ICT as well as quality of service (QoS) are important considerations in the choice of computational resources. In Cloud Computing, users who work within an organisation will increasingly have access to their own cloud service (the "local cloud") and will also be able to access external cloud services. Choices between these options will be made based on security, cost, data and software protection and resilience, but also in terms of technical choices regarding QoS and energy consumption. This paper addresses only the technical choice between a local or remote cloud service, and discusses how this choice can be formulated as an optimisation problem. After providing some experimental measurements regarding energy and performance of servers, we formulate the optimisation problem, describe its solution and present some numerical examples. © 2012 IEEE.