The Value Of Solar Salt Specific Heat Enhancement In Concentrated Solar Thermal Plants
It has been recently reported that nanoparticle dispersions in molten salt mixtures can significantly enhance the specific heat capacity of the salt mixtures. Molten salt eutectics can be used as heat transfer fluids (HTF) and/or thermal energy storage (TES) in a concentrated solar thermal (CST) plant. For either purpose, enhancing their specific heat capacity can theoretically improve CST system performance. However, to date no literature has determined how advantageous an enhancement of specific heat might be in a CST system or its subcomponents. In addition, since there is a cost associated with this enhancement, it is imperative to investigate the net economic limitations and benefits. To address these issues, this paper analyses how HTF specific enhancements in the range of 5-200% influence the CST-tower plant components. The results imply that increasing the HTF specific heat can reduce the storage volume by up to 80%. It was also found that the solar field mass flow rate and parasitic loads can also be decreased by up to 90%, while the net power output of CST-tower plant can be increased by up to 3%. Of course, nanoparticles (or other) costly additives are required to achieve these enhancements. Thus, this study poses the question of what premium could be paid (above the base solar salt cost of 1USD/kg) and still obtain an economic advantage. It was found that if specific heat is enhanced by 30%, a 50% premium on the pure salt is justified. If, however, a specific heat enhancement of 120% is possible (the maximum reported in the literature); a 300% premium yields an economic break-even point. Ultimately, this study reveals that if i) long-term, stable enhancements of 30-120% are indeed possible via the addition of ~1% of nanoparticles and ii) if nanoparticles (e.g. < 30 nm silica spheres) can be mass produced at < 50-200 USD/kg, they will have a significant positive return on investment in CST applications.
Keywordsó Nanoparticle, Specific Heat Enhancement, Concentrated Solar Thermal.