Executive Summary : | Solar energy is one of the prime and abundantly available clean energy sources in the world. Concentrating technologies were incorporated to increase the temperature of the heat transfer fluid (HTF), improving the overall efficiency of the power plant. The HTF used, Solar Salt® (equimolar mixture of NaNO3 and KNO3) has a maximum safe operating temperature of 565°C, limiting the power plant’s maximum possible efficiency. This salt mixture has a freezing point of 223°C (minimum operating temperature), also limiting the plant operating time and the possibility of its use in standalone applications [1]. Taking into consideration the current limitations of Solar Salt®, molten metals and other salts (Hitech) were proposed to replace it. However, the high corrosive nature of liquid metals like molten sodium and the low high temperature stability of Hitech® salts (455°C) paves the way for new material (HTF) development. The current project envisages to develop Ca(NO3)2-NaNO3-KNO3 salt compositions and other ternary salt systems with low melting point in the range 110 – 150 °C and subsequently the modify of these compositions to achieve higher thermal stability (approximately 50 °C improvement) in comparison to the base ternary composition. This will be done by adding a fourth component to the salt. Properties like density, viscosity, thermal conductivity, heat capacity will be measured/modelled. Thermal Conductivity of the salt mixture will be modelled using the Unit Cell model. Thermal heat transfer enhancers (nanomaterials) will later be added to this salt to improve its thermal conductivity. All Properties will be benchmarked against Solar Salt® and Hitech salt® compositions. This final composition will also be tested as a Thermal Energy Storage material by incorporating it in a standalone solar cooker (using Fresnel concentrator) set up custom fabricated to check the feasibility to use this molten nitrate salt for cooking/frying applications. Here the Thermal Energy Storage properties of the salts like heat capacity and cooling curves will be investigated and its performance for cooking /frying applications will be compared using Solar Salt® and Hitech Salt ® as benchmarks. |