An investigation on volumetric absorption system for solar thermal energy conversion and storage

• Optimization of volumetric absorption for carbon based nanofluid in metallic receiver. • Maximum temperature rise of 36.1 °C is obtained for optimum 40 mg/l mass fraction. • A novel theory of integrating a nanofluid based volumetric absorption system with PCM. • The Integrated system is investigated numerically to obtain thermal performance. • After charging, the temperature of nanofluid reaches 51.7 °C, and PCM at 30.7 °C. Solar energy offers a promising alternative to fossil fuels for various domestic and industrial thermal applications. Compared to surface absorption-based conventional flat plate collectors, volumetric absorption in nanofluids has been marked as a great technology providing enhanced thermal efficiency. The present study focuses on the volumetric absorption within amorphous carbon-based nanofluid at stagnant conditions in a metallic (copper-based) volumetric receiver. To obtain the optimized thermal performance, the detailed experiments using various mass fractions (10 mg/l, 20 mg/l, 30 mg/l, 40 mg/l, and 50 mg/l) of amorphous carbon-based nanofluid are conducted. In addition, the receiver’s surface temperature is measured. The maximum average temperature rise above ambient is obtained for 40 mg/l mass fraction, and the value is 36.1 °C for the nanofluid and 33.9 °C for the surface of the receiver. Through the present study, the authors explore the possibility of integrating a volumetric absorption-based solar collectors (VAS) directly with the phase change material (PCM) for thermal energy storage (TES). Based on the experimental results, a computational study is conducted where the metallic (copper-based) volumetric receiver is integrated with PCM (RT31). From the computational investigation, it is obtained that the temperature of the PCM increases with increases in the nanofluid’s temperature. After heating for 5 min, the average temperature of the nanofluid reaches 51.7 °C; correspondingly for PCM, the temperature reaches 30.7 °C with a liquid fraction of 0.36.