Thermoelectric-based all-day solar thermal management
Passive radiative thermal management is reframed as a device-level engineering problem for thermoelectric generators (TEGs) rather than a spectral-material optimization exercise. The surface temperature difference (ΔT) generated by photothermal (PT) absorbers and passive daytime radiative cooling (PDRC) emitters is not equivalent to the effective junction ΔT that drives carrier transport under load; parasitic heat leakage, contact thermal/electrical resistance at electrodes and interfaces, and nonuniform heat spreading systematically degrade the usable gradient. Spectral selectivity sets the upper bound of attainable ΔT, while module architecture, interfacial resistance, and heat-transfer path matching determine whether that bound is preserved as continuous electrical output. The Perspective identifies a critical metrology gap: most reports cite surface ΔT or peak open-circuit voltage without reporting the ΔT-transfer ratio under load, obscuring where thermal losses occur. Because both open-circuit voltage and internal electrical resistance vary with ΔT, external load must be dynamically matched across day-night and weather cycles; night-time reversal of heat-flow direction through the PDRC/PT stack necessitates DC polarity-conversion circuitry, and compact energy storage must buffer intermittent output. The authors argue that fill-factor reduction can preserve junction ΔT by raising thermal resistance but simultaneously increases electrical resistance and suppresses current. Credible assessment criteria are proposed: outdoor 24 h energy density, load-matched power, day-night continuity, and cycle-to-cycle repeatability, rather than peak voltage alone. Near-term deployment targets building-envelope sensors, structural-health monitors, wearables, and distributed IoT nodes where wiring or battery replacement dominates lifetime cost.