Nanotechnology, in particular nanophotonics, is proving essential to achieving green outcomes of sustainability and renewable energy at the production scales needed. Nanomaterials enable optimization of optical, opto-electrical, and thermal responses. Optical harmonization of material responses to environmental energy flows involves large changes in spectral response over limited wavelength bands and tailoring to environmental dynamics. The latter includes engineering angle of incidence dependencies and switchable (or chromogenic) responses. Nanomaterials can be made at sufficient scale and low enough cost to be economical and have high impact on a short time scale. Issues to be addressed include human safety and property changes induced during manufacture, handling, and outdoor use. Unexpected advantages have arisen in this work such as the savings and environmental benefits of cool roofs extending beyond the more obvious benefit of reduced heat flows from the roof into the building. We explore some of the likely elements involved in harmonizing nature and technology with applications of nanophotonics to reduce the use of energy in buildings.