Energy3D is a simulation-based engineering tool for designing green buildings and power stations that harness renewable energy to achieve sustainable development. Users can quickly sketch up a realistic-looking structure or import one from an existing CAD file, superimpose it on a map image (e.g., Google Maps or lot maps), and then evaluate its energy performance for any given day and location. Based on computational physics and weather data, Energy3D can rapidly generate time graphs (resembling data loggers) and heat maps (resembling infrared cameras) for in-depth analyses. Artificial intelligence is also used to support generative design, engineering optimization, and automatic assessment. At the end of the design, Energy3D allows users to print it out, cut out the pieces, and use them to assemble a physical scale model.