Trough system power estimates

Hi,
 
In SAM 2018.11.11, the magnitude from highest to lowest is as follows:  
A. Cycle electrical power output (gross) (MWe)
B. System power generated (kW)
C. Cycle electrical power output (net) (MWe)

In SAM 2013.1.11, the magnitude from highest to lowest is as follows:  
D. Gross electric power output (MWh) hourly
E. Net electric power output (kWh) hourly
F. Hourly Energy Delivered (kWh)

Why does the order changes in the two versions of SAM ?
What is the difference between B and C ?  
Is B the same as F ?

Thanks

Hi Michael,

I'm not sure why the programmers changed the naming convention for those variables between versions 2018.11.11 and 2013.1.11.

In SAM 2018.11.11, the difference between B and C is determined by the "Availability and Curtailment" inputs on the Power Cycle page. By default there is a 4% "constant loss" value that SAM applies to B to calculate C.

The lowest value should represent the electricity delivered to the grid, so I would expect F to be equivalent to C.

Best regards,
Paul.

Hi Paul,

Thanks for your reply.

You mentioned that you would expect C (net output in SAM 2018.11.11) to be equivalent to F (energy delivered in SAM 2013.1.15), Please elaborate further because SAM 2013.1.15 gives net output also?

Are you saying that A=D, B=F, and C=E ?
If yes, then why are the order (from highest to lowest value) changes between the 2 versions of SAM.
In SAM 2018.11.11, it is A, B, then C regardless of input values to SAM.
In SAM 2013.1.11, it is D, E, then F regardless of input values to SAM.

Hi Michael,

The order of the variables is a better indicator of what values they represent than their names because the developers changed the variable names between versions.

Best regards,
Paul.

Dear Paul

I trust you are well.

I am working on a PBT physical model using the 2020.2.29 version of SAM.

I am trying to determine an adequate design cycle thermal efficiency for the Rankine cycle, for which the default is given as 0.356 (my model: air-cooled, ITD @ design = 16 degC, ambient temp @ design = 30 degC, turbine inlet = fixed pressure).

Upon post-processing my results in Excel, I try to "recreate" this efficiency as n_th = W_net/Q_in:
1. Using System power generated / PC input energy
2. Using PC electrical power output: gross / PC input energy

Overall, method 1 produces lower efficiencies than method 2. Regarding this, what is the exact difference between the numerators in 1 and 2 in terms of W_net? Which one provides a better indication of power cycle conversion efficiency given the heat input?

Furthermore, I note these efficiencies from 1,2 are overall lower than the design input parameter. Would this mean that the default design cycle thermal efficiency is not a realistic description of the actual cycle at hand? 
Would it make sense to use option 1 or 2 (depending on which is more accurate) and produce a histogram to determine which thermal efficiency is most frequently encountered in the year, and then update the default thermal efficiency @ design with this calculated value? 

How would one go about to determine a realistic/representative thermal efficiency for the power cycle as a design parameter input? The Chambadal-Novikov relation seems to produce more "realistic" results, especially in the range of 1:
T_H = 373 degC (turbine inlet temp @ design, taken from the SAM PBT documentation).
T_L = T_sat @ P_cond = 8.5 kPa = 42.5 degC at design (8.5 kPa taken from the SAM PBT documentation).
Then, eta_th = 1 - sqrt[(T_L+273.15)/(T_H+273.15)] = 0.301, which is < 0.365.

Any advice on how to best determine this input parameter will be greatly appreciated.

Best regards
Louw

Hi Louw,

For SAM's physical trough model, "PC electrical output: gross (MWe)" is the gross output of the power cycle. It does not account for parasitic loads required for freeze protection or defined under "Plant Energy Consumption"  or "System Availability" on the System Control page. It also does not account for any adjustments made to meet interconnection requirements defined the Grid Limits input page. "System power generated (kW)" is the power delivered to the grid, and accounts for all of these items.

I'll see what my CSP colleagues say about the power cycle thermal efficiency input parameter and get back to you on that.

Best regards,
Paul.