Physical Trough and Molten Salt Tower Questions

1. Is there such a thing as a heat balance diagram that visualizes how the different energy flows in the model correlate to each other? I have been trying to derive the different heat flows from each other, especially concerning the behavior of the solar field, but there seem to be missing links that are not being written to the output files.

We are currently studying our transient equations for startup and shut down. This project should lead to a more complete output of the energy flows in the solar field. It is hoped this will be completed by the end of the year, but it isn’t our first priority.

2. Concerning that: Will there be more outputs in the next release of SAM? The consideration of transient effects makes things complicated, but maybe outputs like "energy to thermal inertia of header" would help the users understand the calculations more thoroughly.

See the answer to question 1.

3. The freeze protection is currently realized as an electric heater system. For molten salt systems, the freeze protection energy requirements get quite high, so I assume that using stored thermal energy would be a lot more economic than using electricity from the grid at night. Are there plans to include the option to run freeze protection from storage in future version of SAM? I currently estimate the output for such a system by adding the freeze protection energy to the annual output and deducting the electricity not generated from TES energy (power cycle efficiency times freeze protection energy). A more detailed model would be appreciated though. I could imagine that in an actual system, a mixer is used to mix salt from the hot storage with salt from the hot header outlet to reach the required temperature at the cold header inlet.

Yes, that is a realistic method to provide energy for freeze protection, but at the moment we do not plan on including it to our model.

4. Another question concerning freeze protection: The energy requirements got much higher from the previous version of SAM from version 2011-06-30 to 2012-12-02. Looking at the energy flows and the temperatures throughout a year the old version assumed a constant HTF temperature in the whole system and thus the use of electric heat tracing throughout the system, while now, at night the HTF enters the cold heater significantly hotter and leaves the hot header at freeze-protection temperature, thus implying a central heater at the cold header inlet instead of heat tracing. Is my understanding of this change in the model correct?

Yes.

5. Concerning the pipe roughness for header pipes and HCE I am a bit puzzled which definition is correct: The header roughness has the dimension m and literature values for the roughness for industrial steel piping have that same value, so this seems okay. The HCE value by contrast is dimensionless and, according to the manual, is a quotient of actual roughness in m and the absorber pipe inner diameter. The manual text is the same for both values, so I wonder which definition holds. Can you elaborate on this?

The header diameters (unlike the HCE diameters) are not fixed, so a dimensionless surface roughness cannot be provided.

6. Are there any changes to be expected for the next SAM release concerning molten salt in parabolic trough systems?

No.

Best regards,
Paul.

does this discussion put end to all questions

Please feel free to post any follow-up questions or comments.

Best regards,
Paul.