Freeze-Thaw Tests on Trough Receivers Employing a Molten Salt Working Fluid Available to Purchase

Several studies predict an economic benefit of using nitrate-based salts instead of the current synthetic oil within a solar parabolic trough field. However, the expected economic benefit can only be realized if the reliability and optical performance of the salt trough system is comparable to today’s oil trough. Of primary concern is whether a salt-freeze accident and subsequent thaw will lead to damage of the heat collection elements (HCEs). This topic was investigated by experiments and analytical analysis. Results to date suggest that damage will not occur if the HCEs are not completely filled with salt. However, if the HCE is completely filled at the time of the freeze, the subsequent thaw can lead to plastic deformation and significant bending of the absorber tube.