SPECTRALLY SELECTIVE HIGH-TEMPERATURE SOLAR ABSORBER COATING TECHNOLOGY
The direct method of harnessing solar energy is the solar thermal conversion using solar collectors. These collectors use spectrally selective absorber surface which has high absorptance (a) in the solar spectrum region (0.3-2.5 µm) and low thermal emittance (e) in the infrared spectrum region (2.5-30 µm). For solar thermal power generation, high-temperature absorber coatings are used in concentrating solar power (CSP) systems. In addition to high absorptance, for CSP applications, low thermal emittance is an important property. This is because the thermal re-radiative losses of the absorbers increase proportionally by T4. In order to increase the efficiency of the solar thermal power plants, solar selective coatings with high spectral selectivity (a/e) and high thermal stability are necessary.
Development of manufacturing capabilities of receiver tubes along with high temperature solar selective coating is essential to realize the objectives of National Solar Mission, which envisages producing 100 GW solar power by 2022. In this endeavour, CSIR-NAL has developed several high-temperature spectrally selective absorber coatings on coupon level samples (up to 150´150 mm2) using sputtering processes. The know-how for development of technology for commercial production of the absorber coatings is available with CSIR-NAL (TRL-6). Efforts are currently underway to explore the possibility of upscaling these lab scale technologies in collaboration with the industry.
PVD coated high temperature solar selective absorber.