Solar Selective Absorbers Based on Semiconducting Thin Films

Abstract

In order to produce CO₂ free hydrogen using thermal energy at high temperatures, concentrated solar power systems are one of the most promising candidates. For mass production of hydrogen, linear focusing systems consisting of parabolic trough mirrors are suitable because of the high scalability of the power plant capacity. Although most of the conventional linear focusing systems have been operated under 400 °C, higher temperatures are desirable for more efficient solar-thermal energy conversion and hence for lower cost of hydrogen production. A key component in the linear focusing systems is solar receiver tubes with “solar selective absorbers” by which concentrated solar radiation is absorbed and thermal infrared radiation is inhibited at the operating high temperatures. This chapter introduces novel solar selective absorbers for efficient and durable solar-thermal energy conversion operating at 650 °C. The solar absorptance has been enhanced by band-edge absorption of semiconducting β-FeSi₂, and the infrared emissivity at high temperatures has been reduced by thermally stabilized silver (Ag). The optimally designed multilayers achieved the averaged solar-thermal conversion efficiency of 87% between 300 and 650 °C, and ensured superior thermal durability over 25 years under high temperatures.