Choosing Thermocline TES results in a Warning from TRNSYS

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Choosing Thermocline TES results in a Warning from TRNSYS


I'm not used to simulation softwares such as SAM, so maybe my mistake is trivial, in any way, every help is appreciated:

My intention in running a simulation on a 20 MWe CSP Tower plant is to get some data and numbers, LCOEs, total costs, annual production, the farthest I got was using the SamUL from the sample file and running it to find a decently enough minimized LCOE output for some solar multiples with 15h TES.

Now I decided to test thermocline TES, and after simulation, I get a warning, always the same, I already tried changing input values that seemed relevant, and the warning remains. Loading the Gemasolar comparison (sam_case_csp_salt_tower_gemasolar_2013-1-15.zsam) and switching it to Thermocline gives the same warning. The sample file and the file associated with the latest reports (sam-costs-2013-molten-salt-power-tower.zsam)

Here is the warning

"trnsys.tower: WARNING: The temperature for Salt (60% NaNO3, 40% KNO3) was outside of the fluid's operating range of 220.- 593. [C] for at least 50 time steps. The fluid temperature on the 50th occurrence was ***** [C] at timestep 27.0. Try changing the design parameters or fluid to ensure operating temperatures stay within the range."

As a reference, starting a new project and only switching from two-tank to thermocline also produces the warning after running the simulation.

Even though I could not find any crass visible error or inconsistency with some basic graphs in the simulations with the warning, I decided not to go ahead and use the data due to possible "hidden" modeling math errors.

I did read the help files and some literature on thermocline use on CSP Molten Salt Power Tower, my issue is probably at understanding of the software, or so I hope.

Any insights or suggestions?

Thank you in advance.


Paul Gilman

Dear Dan,

Sorry it has taken me a few days to get back to you. I needed help from the CSP on this question.

It turns out that there is a bug in the Thermal Energy Storage code that is causing the warning message to appear even when the storage fluid temperature does not fall outside its operating limits. As a workaround for this issue, you can ignore the warning, and look at the values of the hourly results "Thermocline: Cold node temperature (C)" and "Thermocline: Maximum temperature (C)" to make sure that those values are not falling outside of the acceptable limits for the fluid.

We have fixed the bug internally so that the message will not appear, and will include the fix in a future version of SAM.

Best regards,

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