Question: I try to change the physical parameters of Solar Salt in the TES system via the "user-defined HTF" function in order to track changes in the system's annual energy as a function of the physical parameters of Solar Salt. In order to adjust the physical characteristics of Solar Salt while keeping the “Storage volume” constant, I also modified the “Full load hours of TES” at the same time. However, the result doesn't seem reasonable (please see the attachment for details), therefore I would like to know whether my calculation result and operation method are accurate and if you could offer some advice.
Answer:
The thermal conductivity parameter is not used in the TES system model, where the heat transfer/loss out the tank walls is captured by the "Wetted loss coefficient" parameter. The effect of viscosity is captured within the parameter "Pumping power for HTF through storage". These reasons are why you are not seeing any effect from changing these two parameters.
However, the specific heat and density will certainly affect the storage energy per volume, where a storage fluid having lower specific heat or lower density will cause storage to charge and discharge more quickly. You are already seeing the effect when you're adjusting the "Full load hours of TES". However, these properties will not have a linear effect on annual energy because they are only applicable at times the storage is full, i.e., it can't charge more and thus the field must defocus resulting in lost energy (lower annual energy). However, even then, some of that energy will not be lost because the power cycle can operate above nominal when "Maximum turbine over design operation" is greater than 1.
