Preamble: Solar energy is an unlimited source of renewable energy, which can be utilized in energy production to generate both heat and electricity. India is a tropical country, and solar energy is abundant throughout the year. Solar thermal conversion is the simplest and most direct method of harnessing solar energy. In the late 1980s, CSIR-NAL developed NALSUN solar absorber coating technology for domestic water heater applications using the electrodeposition method. However, the coating bath is carcinogenic owing to the presence of hexavalent chromium, and its disposal is a challenge. In addition, there is a need to develop a costeffective, eco-friendly, and easily scalable coating technology that is not available in the country.
Current Level of Technology: CSIR-NAL has developed an eco-friendly sprayable spectrally selective coating for domestic solar water heater applications. The spectrally selective coating consists of two layers: an absorber layer and an inorganic protective layer. The coating was sprayed manually on 2 m long Al fins, and a solar water heater panel was fabricated. The photothermal conversion efficiency of the NALSUN-NG panel is 70% with heat loss coefficient of 4.36 W /m2C. The coating has qualified all the environmental tests as per the International Energy Standards. Based on the test results, the service life of the coating is expected to be more than 20 years.
5.Salient Features of NALSUN-NG Coating
• Non-hazardous raw materials
• New absorber coating formulation
• New inorganic protective layer formulation
• Environment-friendly water borne coating
• High solar absorptance (0.91-0.93)
• Low thermal emittance (0.21-0.30) at 82°C
• Thermally stable in air at 175°C for 600 h
• Developed on metal substrates (Al, GI, etc.)
• No volatile organic compounds
• RoHS and REACH compliant
• Uses very simple effluent treatment process
• Easily scalable and cost-effective spray process
