With the rising energy demand in ICT services and its associated environmental impact, the need for energy efficient Enterprise ICT solutions is growing. As data centres account for a large part of energy consumption in ICT, data centre operators strive to create opportunities to put more emphasis on reducing energy consumption. However, creating ICT Systems that are energy efficient by design remains a key challenge. In this paper, we identify and map contextual energy information about data centre operations in order to model their power related components. This contextual modelling is then mapped to deployment diagram where we introduce greenUML (gUML), an extension to UML diagrams to improve energy efficiency through energy analysis at design time. gUML will allow system architects to reason about the energy footprint of their applications at design time.