Negative electric power

Dear community,

I am simulating a CSP plant with central tower technology. When I get the results, there are certain hours that I have a negative generation. What would be the physical explanation for that? How is it possible to have a generation less than 0? I would really appreciate if you help me understand it. I am attaching an image to make it a little clearer.
Thank you very much in advance,
Francisco

Hi Francisco,

Negative power indicates that the system is consuming more power than it generates. In the case of a CSP power tower system, SAM models parasitic loads for electric pumps and heaters that circulate and heat the HTF at night to prevent it from freezing.

Best regards,
Paul.

Thank you very much for your kind reply Paul. One last question please. I think that in previous versions of SAM, for CSP technology it was possible to define the "Storage Distpach" (w / solar or w / o solar). Currently that is not possible anymore? Now I only have Turb. ouput fraction. Or maybe I'm looking wrong.
Thank you,
Francisco

Hi Francisco,

As of SAM 2020.2.29, the Physical Trough model uses a new dispatch control algorithm in place of the old manually controlled method. See the Help topic for the System Control page for a description of the algorithm. It is also described in Wagner M (2018) "Optimized Dispatch in a First-principles Concentrating Solar Power Production Model" available under "Power Tower" on the CSP publications page: sam.nrel.gov/concentrating-solar-power/csp-publications.html .

If you have a reason to use a model with the old dispatch method, you can download SAM 2018.11.11.

Best regards,
Paul.