The rapid urbanization and growth of megacities have intensified the demand for energy solutions that won’t harm the planet. Since nearly two out of every five units of energy used worldwide goes to powering buildings, improving how these structures consume energy is critical. Taking action here helps lower emissions and supports international commitments, such as the 2050 net-zero target. Large solar installations have become important in renewable energy, but issues like land demands, expensive setups, heavy machinery, and upkeep challenges slow their spread. Similarly, conventional solar heating systems often require significant upfront investment, ample space, and depend on weather, which limits their use in urban areas. To overcome these hurdles, advanced photothermal technologies offer a fresh approach to harvesting solar power, designed to efficiently support both heating and cooling functions. These transparent multilayer photothermal films are built to capture light from the sun and indoor sources in all directions. They turn that light into heat efficiently without needing big equipment, making them perfect for tight city spaces. During hot seasons, clear solar panels placed on building exteriors and inside—like on walls, floors, and ceilings—help gather energy from sunlight by day and indoor lights at night or on cloudy days. This technology offers subtle but powerful heating and cooling solutions, especially for tall buildings in urban areas. Building on this idea, the Photothermal Solar Tunnel Radiator (PSTR) uses plasmonic nanomaterials to turn both direct sunlight and scattered light into heat efficiently. It fits smoothly with modern building designs, helping meet sustainability goals. Additionally, new methods that capture indoor lighting help create energy-neutral buildings by going beyond traditional solar panels. By using different types of light, these buildings generate electricity more consistently and also provide energy for heating and cooling throughout the year. Together, these approaches offer scalable, affordable, and eco-friendly solutions for sustainable urban energy systems. This chapter is among the latest studies investigating how plasmonic nanoparticles can be used for heating and cooling in buildings—a shift from earlier work that focused on medical applications. By taking advantage of transparent thin films, strong absorption in ultraviolet and infrared ranges, and combining multiple panels to boost solar energy capture, this new method offers a fresh route for green energy production. Plasmonic nanoparticles enable efficient harvesting of energy across a wide spectrum while maintaining transparency, which fits well with building designs. This blend of cutting-edge materials and sustainable energy approaches showcases how nanotechnology can play a key role in solving today’s energy challenges.