Improving the thermal properties of NaNO3-KNO3 for concentrating solar power by adding additives

•Heat transfer and storage medium for Concentrating Solar Power.•Melting points of mixed nitrate salts are about 100 °C.•Decomposition temperatures of mixed nitrate salts are about 600 °C.

Concentrating Solar Power (CSP) system with storage can provide consistent power and thus are attractive relative to intermittent power sources, e.g., solar photovoltaics and wind. Mixed molten salt is a promising medium for both heat transfer and energy storage in solar thermal power because of its many advantages such as large heat capacity, low vapor pressure, low cost, wide range of temperature in application, etc. However, there are the disadvantages of higher melting point and poor thermal stability with the commonly mixed molten salts, such as Solar salt (60 wt%NaNO3+40 wt%KNO3, melting point @220 °C, limit use of temperature @565 °C). In order to obtain molten salt with lower melting point and better short-term thermal stability, 14 kinds of mixed molten salts are obtained by adjusting the component ratio and adding carbonates or nitrates based on Solar salt. Through the Differential Scanning Calorimetry (DSC) and Thermogravimetric (TG) methods, their melting point, crystallization point, thermal decomposition temperature and short-term thermal stability are measured. 4 kinds of mixed molten salts are selected preliminarily at last. Their melting points and decomposition temperatures are about 100 °C and 600 °C respectively. They show good short-term thermal stability in the 4-days repeated heating-cooling experiments. The specific heat and sensible thermal storage cost of preferred molten salts were also obtained.