Transparent thermal storage for dispatchable solar thermophotovoltaics

Solar thermophotovoltaic systems promise high theoretical efficiency together with intrinsic dispatchability through integrated high-temperature thermal storage. Yet, existing designs either neglect storage or rely on opaque media that act as thermal buffers between the solar absorber and thermophotovoltaic (TPV) emitter, creating large temperature gradients that limit emitter temperature and overall system performance. Here we introduce transparent thermal storage , in which the storage medium itself participates in radiative energy transport. Using a transient one-dimensional conductive–radiative model coupled to an effective thermodynamic description of TPV conversion, we compare opaque and transparent storage configurations over a representative charge–discharge cycle. System performance is assessed using two complementary metrics: total solar-to-electric system efficiency and post-illumination dispatch efficiency. Allowing concentrated sunlight to penetrate the storage and be absorbed near the emitter suppresses conductive bottlenecks, enabling higher emitter temperatures, reduced radiative losses, and improved efficiency-dispatchability trade-offs. While transparent media deliver the best performance, semi-transparent materials – transparent to solar radiation but opaque at longer wavelengths – can provide intrinsic spectral selectivity through solar thermal trapping, thereby reducing optical losses without relying on high-temperature selective coatings. These results establish transparent and semi-transparent storage as promising system-level design strategies for modular, efficient, and dispatchable solar energy conversion with integrated thermal storage.