Driven by both the global energy crisis and environmental challenges, the development of efficient, clean, and sustainable energy technologies has become an urgent necessity. In this context, self-powered technology based on space energy capture has emerged. This review focuses on an integrated power generation system that can synergistically utilize two major heat sources—the sun and the cold space—to establish a heat transfer channel on the Earth′s surface, thereby achieving an integrated power generation system with all-day uninterrupted power output. The technology captures solar radiation energy through photothermal conversion, uses the radiative cooling effect to release surface heat into outer space through the atmospheric transparent window, and directly converts the resulting temperature difference into electrical energy using thermoelectric conversion devices. The article systematically summarizes recent research progress in the design of nanomaterials, device structure optimization, system integration strategies, and typical application scenarios. It provides an in-depth analysis of the system′s day-night operating performance, environmental adaptability, and key evaluation indicators, while also discussing the main challenges associated with spectral selectivity control mechanism, thermal management structure design, and large-scale application. This technology provides a maintenance-free, zero-energy-consumption sustainable energy solution for realizing smart sensors, wearable electronic devices, and power supply systems in remote areas, and has significant potential to drive energy technology innovation.