Evaluation of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field

An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating SEGS plants currently use a high temperature synthetic oil consisting of a eutectic mixture of biphenyl/diphenyl oxide. The scope of this investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems existed, and the quantification of performance and electricity cost using preliminary, but reasonable, cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO₃ and 40% KNO₃) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% Ca(NO₃)₂, 7% NaNO₃, and 45% KNO₃).