Negative LCOE values from Physical Trough model

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Negative LCOE values from Physical Trough model


I have been running some parametric studies to help optimize the storage/size of a parabolic trough system using LCOE (nominal) as my target In my attempts to do so I keep getting results that show a (very large) negative LCOE which I assume is being caused by a relatively small negative energy generation. I am a bit stumped as to the cause and was wondering if there was any insight that you could provide?

Here are some relevant details of my SAM model;

I have been running a physical trough model to sync up with a power cycle design in a region in southern California. The details of the power cycle have been worked independently of SAM and I am looking to design a trough system to match up with this existing Rankine cycle.

That being said, several variables are constrained by this Rankine cycle and I suspect they may be causing these erroneous values. I am also showing linear relationships between Hours of Storage/Size of Plant and LCOE (i.e. larger plants with less storage are ALWAYS better).

Anyway, here are the variables I am having trouble with:

Irradiation at design: I am using a value of 950 W/m^2 based on the recommendation of looking at the maximum of the DNI-cosine effect product

Freeze Protection: I am using 150 C in accordance with the HTF I am using (Hitec)

Design Loop Inlet Temp: Here is where the confusion begins for me. I have no idea what this should be set at. SAM help says that this temp is set to the power cycle's design outlet temperature is equal to this value; and I have temperatures at many different points of the Rankine system I have designed but I'm not sure what this should be set to. The temperature of the steam before the boiler? After the Condenser? Right now I have it set to 200 C but this is just to prevent the HTF from freezing and stopping the simulation cold.

Design Loop Outlet Temp: Similar problem here. The rankine system I have designed uses a max T of 400 C so I assume that the outlet temp of the HTF loop needs to be higher than 400 C for this to work. I set it to 450 C somewhat arbitrarily.

Design Gross Output: I am using 100 MWe with a gross to net conversion factor of 1 given that the Rankine system I analyzed has an output of 100 MW.

I am using option 2 for the solar field parameters and then optimizing using field aperture and Full Load Hours of TES (I am using a direct system as well if that matters).

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