Thermal and hydraulic evaluation of a linear Fresnel solar collector loop operated with molten salt and liquid metal

Abstract

In this paper, results of a thermal-hydraulic analysis of a linear Fresnel solar collector loop using molten salt or liquid metals as heat transfer fluid are presented. The purpose of this study is to compare the benefits and challenges of using liquid metals (e.g. sodium) or molten salts (e.g. solar salt) as heat transfer fluid into line focusing Solar Thermal Electric plants. Similar studies have been conducted for point focussing Solar Thermal Electric plants but line focussing plants have not been thoroughly investigated yet. After reviewing and comparing the main thermo-physical properties of sodium and solar salt, results from thermal-hydraulic simulations, using the best-estimate system code TRACE from the US Nuclear Regulatory Commission, are presented for various plant operation scenarios. The results show that sodium offers several advantages over solar salt when used as heat transfer fluid, among which: wider operation temperature range, faster start-up procedures, quicker response of the control system and ultimately potentially higher energy yield, mostly thanks to its hundredfold higher thermal conductivity. These benefits may result in increased interest into this technological concept and might lead to further developments of Solar Thermal Electric plant design with reduced levelised cost of electricity generation.