Passive Solar Heat Transfer via Photothermal Skins for Capability-Enhancing Building Retrofits

Rising energy costs in dwellings cause a significant negative social impact, creating energy insecurity. In the United States, over 33 million homes report forms of energy insecurity, with over 24 million residents, often renters, reporting reducing or foregoing food or reducing energy consumption to minimize energy costs. Here, we describe a straightforward yet underexplored method of heat generation and delivery, photothermal heating through walls, that can be adopted by individual tenants to improve the thermal conditions of their homes without compromising their health or housing security. We detail a lightweight fabric-based photoactive skin that is designed to be used as a removable additive layer over existing walls, and demonstrate its performance as capability enhancers that passively increase the temperature of indoor environments. Photons are leveraged as a free, widely distributed energy source, a light-absorbing polymer is used to convert the energy contained in photons into heat, and the heat thus generated is directly transported into building interiors through the building envelope. Outdoor tests with physical house models prove that a 4.8 °C increase in interior temperature can be realized over a single day-night cycle by loosely affixing a photoactive skin to one face of the overall building envelope. Building energy simulations reveal that the supplemental heat created by wall photothermal heating can lead to a 15% reduction in heating energy demand for a standard residential building, with a maximum reduction of 23% projected for a large 16-story residential structure in northern latitudes.