Thermal energy absorbed and Solar field thermal output

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Igor
Thermal energy absorbed and Solar field thermal output

Hello

I am trying to simulate a parabolic trough collector thermal plant. I have been studying the results from SAM and I understand the sequence of calculus of thermal parameters but I have still some doubts with some of these parameters:

1. I would like to know how is obtained the parameter “Thermal energy absorbed”. I have calculated this parameter with the following formula:

Thermal energy absorbed = Total incident thermal energy * Collector average optical efficiency - Receiver thermal losses

Nevertheless, I have found some differences among my results and SAM. What other parameters are used to obtain “Thermal energy absorbed”?

2. I don’t understand the step between the “Thermal energy absorbed” and “Solar field thermal output”. I see that “Solar field startup energy” affects to the value of “Solar field thermal output”, but it is not the only parameter that affects. What is the “Solar field startup energy”? What other parameters affect to the “Solar field thermal output”?

I am working with the version 2012.5.11

Best regards

Igor

Paul Gilman

Dear Igor,

For SAM's physical trough model, you can refer to the Technial Manual for the SAM Physical Trough model for an explanation of the energy calculations. For a link, see the citation under Concentrating Solar Power (CSP) Models on the Performance Models page of the SAM website.

You can also study the source code itself. The source code files are in the SAM installation folder, and are listed for each CSP model in the model's overview topic in Help. For example, for the physical trough model, you can find the list of source code files in Help under Concentrating Solar Power, Parabolic Trough Physical, Trough Physical Overview.

Best regards,
Paul.

Igor

Dear Paul

I have read the Technical Manual and part of the code but I have still the same doubts.

I think that I have understood the physical meaning of the parameter "Thermal energy absorbed": is the thermal energy absorbed by the collectors, before thermal losses and including optical losses. Nevertheless, I can't fit my results with those of SAM.

Moreover, I don't understand the parameter "Solar field thermal output". I have studied the results from SAM and it seems that "Solar field thermal output" is, more or less, the Thermal energy absorbed less the Solar field startup energy and the piping losses. What is the meaning of the Solar field startup energy? Why it has values different from 0 during the day?

Can you explain me these parameters? I have found no answer in the manual. Please find attached an Excel spreadsheet with my calculations and my differences with SAM.

Thanks in advance

Igor

Igor

Dear Paul,

I continue with my doubts. I think that I can't fit my results with those of SAM due to the defocusing of the colector.

Nevertheless, I continue ignoring what is the meaning of the "Solar field thermal output", where is this parameter measured in a solar plant.

Thanks in advance

Igor

Paul Gilman

Dear Igor,

The solar field thermal output is the thermal energy at the solar field outlet:

trough solar field thermal output

Best regards,
Paul.

Xivonne

Hi Paul,

I have read "Technical Manual for the SAM Physical Trough Model." Wagner, M. J.; Gilman, P. (2011).
and this other

"Draft CSP Reference Manual" Friday, December 05,2008 (https://www.nrel.gov/analysis/sam/pdfs/sam_csp_reference_manual_2.5.pdf ); but it doesn't the same than the actual version, because of the change of the names of the results.

Could you recommend me an actualized article about the SAM's results?; I don't know where I could found the warm up of the solar field and the meaning and formulation of these others parameters:

1. “Thermal energy absorbed (MWh), hourly”. Is it correct that Igor says?...Is it the energy that is absorbed by collectors?....and why is negative?

2 How I could calculate the warm-up energy of the solar field?

3 And the energy that is necessary to start up the power block?...I only can see the "Solar field startup energy (MWh), hourly"......

Pt: I want to see the results formulation and it's meaning

Please give me clear answers

Regards

Paul Gilman

Dear Xivonne,

Could you recommend me an actualized article about the SAM's results?

The physical trough reference manual (see the Performance Models page for a download link) is the most up-to-date publication describing SAM's physical trough model. We have tried to use descriptive labels for SAM's output variables so that you can understand what they represent from the label and units.

1. “Thermal energy absorbed (MWh), hourly”. Is it correct that Igor says?...Is it the energy that is absorbed by collectors?....and why is negative?

Yes. That value represents the thermal energy absorbed by the collectors in the solar field. It is negative during nighttime hours when freeze protection energy is required.

2 How I could calculate the warm-up energy of the solar field?

The field warm-up energy calculated is part of the "nodal energy balance calculation" described in Section 2.1.1 of the reference manual. The role of startup energy in the calculations is described in the example starting at the bottom of p 11 at the end of that section. I don't think there is a way to replicate that calculation by hand. You can see the calculations in the source code file sam_mw_trough_Type250.f90 -- just search the file for the keyword "startup." The source code files are in the \exelib\trnsys\source folder of your SAM installation, which by default in windows is C:\SAM\2013.1.15.

3 And the energy that is necessary to start up the power block?...I only can see the "Solar field startup energy (MWh), hourly"......

The power cycle startup equations are described in Section 3.4.2 of the physical trough reference manual.

Best regards,
Paul.

alsam

Dear Paul,

I am using the SAM 2015.6.30 Version for the simulation of a parabolic trough solar plant.

I would like to know, what does the "Field HTF energy inertia (consumed) (MWh)" represent?

Does it account for the thermal energy that is consumed during the heating up of the pipes and the HTF to the working temperature (thermal capacity of the header/runner pipes and fluid) or only for the heat capacity of the fluid?
Is the field thermal power produced calculated according to the following formula?:

Field thermal power produced=Incident solar energy*optical efficiency-Receiver heat losses- Header pipe heat losses-HTF energy inertia

Best regards,
Alex

Paul Gilman

Dear Alex,

Please see Section 2.1.1 of Wagner (2011) listed under "Physical Trough Model" on the Performance Model Documentation page of this website:

https://sam.nrel.gov/performance

Best regards,
Paul.

alsam

Dear Paul,

thanks for the reply. I have already read this section in the manual and as I unsterstand, the field HTF energy inertia accounts not only for HTF thermal intertia but also for the piping components inertia. Am I right?

Nevertheless, I still doubt, whether the field thermal power produced is calculated according to the equation that I write above or according to the classic formula Q=m*Cp*(Tsys,h-Tsf,in).

Best regards,
Alex

alsam

Dear Paul,

excuse me for sending to you again. But I would need an answer as soon as possible about my question regarding the Field HTF thermal inertia, that I asked above, because I write a master's thesis and it is important for me.

What does it really represent? Does it account only for HTF thermal intertia or also for the piping components inertia? It is not so clear for me..
And so the field thermal power output is: Absorbed energy-Field HTF thermal inertial?

Thank you in advance.

Best regards,
Alex

Allana

Dear Paul,

I am reading the Technical Manual for the SAM Physical Trough Model and can not find out how the solar irradiance relates to the net output electrical power. The differential equations of internal energy are based on the change of temperature with time. Where do I find the relationship of solar irradiance with temperature or internal energy?

Thank you in advance.

Best regards,
Allana.

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