CLFR in SAM

Dear Gentlemen,

There is a paragraph in SAM Help as follows :
The linear Fresnel model can also be used for compact linear Fresnel reflector (CLFR) systems by using the appropriate coefficients with the polynomial heat loss model for the receiver geometry and heat loss parameters on the Collector and Receiver page.

Could you please give an example for this.

Regards
Rahmi

Dear Rahmi,

Unfortunately, we do not have the resources to develop a sample file for a CLFR system. The method for modeling a CLFR system in SAM is not different from the method for other types of linear Fresnel systems, so you can use the sample file that comes with SAM as a starting point. We developed that file with Novatec to describe their system.

To model the CLFR or any other linear Fresnel system in SAM, you need to provide SAM with data that describes the collector efficiency and receiver heat loss parameters. Those inputs are on the Collector and Receiver page where you provide a table of collector optical efficiency values and a set of receiver heat loss coefficients. You either need to generate those values yourself using your own models, or get them from the equipment provider.

For more details about SAM's linear Fresnel model, please see the references under "Linear Fresnel" on the Performance Models page of the SAM website .

Best regards,
Paul.

Hello Rahmi,

To follow up with more detail on the CLFR aspect of your question, there are a few changes you'll need to make in the model to capture the unique flow path layout of CLFR. Since a single collector row contains both the outbound and return fluid flows, energy reflected into the receiver from the collector panels is absorbed by the outbound and return flow streams equally (assuming the superheated steam has the same residence time in a collector as the boiling steam). Although this arrangement is different from the geometry presented in the SAM Linear Fresnel interface, there is no barrier within SAM to modeling a CLFR system.

The key to modeling CLFR is to temporarily ignore the geometrical arrangement of the flow path and consider only the energy balance along the flow loop. The SAM Linear Fresnel solar field model determines the amount of thermal energy entering the fluid flow by multiplying collector optical efficiency by available DNI and collector reflective aperture area. If half of the energy incident on the CLFR receiver enters the outbound flow and half the return flow, you can model this by doubling the number of collector units in the loop, and halving the reflective aperture area per collector.

To be more specific, you can model CLFR using the following general methodology:

1) On the Collector and Receiver page, input the optical efficiency for the collector system. Assuming the collector geometry is consistent throughout the loop, you'll put in the efficiency values for a collector unit as it would perform in the field.
2) Use the polynomial heat loss model (the evacuated tube model is not appropriate for this application).
3) Input receiver heat loss parameters based on vendor data or external model results, if available. The heat loss should represent the performance sequentially along the flow path as the steam heats up. Heat loss will differ between the outbound and return flow tubing, even in tubing that is adjacent within the same receiver enclosure.
4) Ensure the settings for the superheater sections match the expected performance for your system if you choose to specify superheater performance separately. If you would like to use the same optical and thermal performance inputs for both the superheater and boiler sections, uncheck the "Superheater has unique geometry" option on the Solar Field page.
5)
(a) Take the reflective aperture area associated with each collector unit for the actual CLFR system you're trying to model and divide the value in half. Input this value as the Reflective aperture area on the Collector and Receiver page.
(b) Double the number of collector units you're modeling to reflect the number of times the flow path passes through a collector unit. If you have 8 modules in a CLFR "loop", you will end up with 8 outbound and 8 return loops, for a total of 16. Some of the nodes along the return path will be superheater modules (SAM only models superheat systems), so you'll need to adjust the value to reflect the amount of superheat you want in the system. Using the default temperature assumptions, you would have 12 boiler and 4 superheat modules.
6) Ensure your pressure drop and other model values are appropriate for the system. Pay particular attention to the Length of the collector module (Collector and Receiver page), which should be equal to the length that the flow path travels (once) through a collector node. Also note the Tracking power value (Parasitics page), which you will likely want to divide in half since the number of modules has artificially been doubled. In terms of plant costs, take care to ensure the land usage is representative of your system. You may need to do land usage calculations outside of SAM and scale the land cost input accordingly to match your projection.

After making these changes, you should be ready to run a CLFR-type analysis.

Best,

Mike Wagner
NREL

Dear Mr. Michael Wagner,

Endless thanks for your patience and interest.

Kind Regards,
Rahmi

Dear Mr. Michael Wagner,

Endless thanks again for your patience and effort.
SAM is a comprehensive software, I am also new in SAM and energy calculations.

Because all the values in the example project for LFR in SAM are for Novatec Solar,
if a LFR or CLFR project is using Novatec collectors and receivers, all the values
in "Collector and Receiver" can be used.

The project on which I am studying is CLFR. Therefore, "Steam temeperature adjustment" values in "Polynomial fit heat loss model" must be adjusted. There are two values for Cx in the page : C1=0.671 and C2=0.00255996
Are they also sended from Novatec Solar ? If so, we can also use them for CLFR.

Could you please say us whether they must be divided in half or multiplied by two.

Kind regards,
Rahmi