Continuous Integration (CI) is a widely used quality-assurance measure within software development. It empowers developers to spot bugs and integration issues early in the development cycle and helps to maintain a coherent codebase, both in terms of quality and styling, even in open-source environments. But CI might have a hidden cost. Projects need to be built and tested continuously throughout the development cycle. It is not uncommon for projects to have multiple commits per day, reaching thousands of commits per year, with each commit having one or multiple build and test cycles. In this thesis, over 200 open-source Java projects were measured with the aim of making developers more aware of how much energy these builds can take and the measures that can be taken to reduce energy consumption where possible.