Energy efficiency and the associated quantification of performance data present companies with major challenges for the brownfield. ISO 50001 plays a major role, particularly against the backdrop of increasing regulatory requirements at national and international level. Due to rising taxation and energy prices, the economic aspect of eco-efficient production is also becoming increasingly important. To be able to indicate the current status of production in key performance indicators (EnPIs), it is necessary to precisely quantify energy in the context of production. This work shows an approach for the integration of combined measurement approaches for electrical power in existing industrial systems. In addition to mobile solutions, static sensors with an Open Platform Communications Unified Architecture (OPCUA) and Internet of Things (IoT) interfaces are used for seamless data integration and processing. A core aspect of the work is the development and description of a materiality matrix to determine the systems that need to be considered for optimization and simulation. This paper demonstrates the applicability of the approach and describes the implementation of power measurement. The results show that this approach is an effective method for ISO 50001 compliant measurement. This serves as a basis for optimization in the brownfield and simulation for the greenfield.