We develop an environmental management information system (EMIS) that provides economic and environmental data to suppliers and consumers of electrical energy. This information-sharing fosters sustainable decision-making in accordance with individual preferences and results in time-shifting energy consumption, which ultimately improves the alignment of power supply and demand. In turn, this enhances the integration of renewable energy systems, reduces the use of fossil fuels, and increases energy efficiency. We develop the EMIS based on established architectures and embed it into the Energy Informatics Framework, where it is supposed to operate at the interface of energy supply and demand in a smart grid environment. To conceptualize, design, and evaluate the developed system, we rely on the well-acknowledged research methodology of design science. In line with that, we demonstrate the utility of the EMIS and discuss its benefits regarding sustainability aspects by means of a comprehensive scenario analysis. To sum up, the proposed EMIS applies the promising integration of energy and IS research by means of Energy Informatics and responds to the necessity of incorporating environmental sustainability aspects into both corporate and consumer decision-making.