what is the design point used by SAM in "CSP molten Salt Power Tower

my following question are about the "solar multiple",the"Design Point" and the "calculation of mirror surface needed".
when I use "CSP molten Salt Power Tower" to simulate a 50MW tower case,i have found that SAM seems use the summer solstitial solar noon,may be 12:00 of June 20th.
since the SM(design point)=Q(th,solar field)/Q(th,power block),my question are

1.is SAM use this SM definition? Q(th,solar field)is the energy arrived on the receiver surface or the receiver thermal output?

2.in hourly results,i think "Solar field optical efficiency hourly" is "the energy arrived on the receiver surface" over "the energy arrived on the mirror surface", that is to say,the efficiency includes Field availability,Incidence cosine,Shading and Blocking factor,‘Spillage’ or intercept,Atmospheric attenuation with distance, etc.am i correct?
why according to the hourly results,my calculted mirror surface differs from SAM's result?

3.what is the design point used by SAM in "CSP molten Salt Power Tower"?or how does SAM calculate the mirror surface needed?

Hello,

1. SAM uses the solar angles at noon on the summer solstice for the design point calculations.

2. For the power tower models, Hourly Solar Field Optical Efficiency = Hourly Thermal Energy Incident on Receiver *MWh) / Hourly Total Incident Thermal Energy (MWh).

3. The field optimization wizard calculates the optimal number of heliostats in the field. The dimensions of a single heliostat determines the reflective area of a single heliostat (length x width for rectangular heliostats, and width/2*pi for circular heliostats). The total reflective area is the number of heliostats x heliostat area.

Best regards,
Paul.

Hello Paul,

I would like to know to which extent that SAM consider the atmospheric attenuation between the heliostat field and the central receiver? is SAM applying any factor?

Thank you.

Dear Juan,
Yes, SAM's power tower models account for atmospheric attenuation of the heliostat image as it passes through the air to the receiver. For details, please see Wagner 2008 "Simulation of Direct Steam Power Tower Concentrated Solar Plant," Section 2.1.1 "Losses from the Heliostat Field." Atmospheric attenuation is described beginning on p. 31.
For a link to this and other reference documents, please see the Performance Models page of the SAM website.
Best regards,

Paul.

Thanks for your response, Paul.

I have read section 2.1.1 and I suppose that SAM is using as a basis the Solar II visibility conditions, no matter the conditions of the plant, is this correct?
In that case, can these conditions be changed?

Thank you.

Dear Juan,

No, the assumptions for atmospheric attenuation are not editable in SAM.

Best regards,
Paul.