Calculating System Efficiency for Trough and Tower Systems

SAM's power tower models do not report the annual solar field efficiency, receiver thermal efficiency, or power cycle efficiencies. However, you can calculate the values by exporting hourly data to a spreadsheet, and calculating the annual values from the hourly data there.

Solar field efficiency = (Thermal energy on receiver) / (Total incident thermal energy) x 100%

Receiver thermal efficiency = (Receiver thermal power output) / (Thermal energy on receiver) x 100%

Annual gross cycle efficiency = (Gross electric power output) / (Receiver thermal power output) x 100%

Gross to net efficiency = (Net electric power output) / (Gross electric power output) x 100%

After running simulations, display the hourly variables on the Results page, and then export the data to a spreadsheet program:



See the attached Excel workbook for an example of how to make the calculations in a spreadsheet.

Best regards,
Paul.

Hi Paul !

I am trying to calculate solar field efficiency, receiver thermal efficiency with SAM(2011.12.2) monthly in parabolic trough physical model,how should i do ?

Thank you for your kind help !

joe-hq

For the physical trough model in SAM 2011.12.2, the efficiency calculations for the hourly values are as follows:

Total Incident Thermal Energy = Total Aperture Area * DNI

Incident energy-cosine effect product = Total Incident Thermal Energy * cos(incident angle)

Collector average optical efficiency = Thermal energy absorbed by receiver (before thermal losses) / Incident energy-cosine effect product

Thermal energy absorbed = Thermal energy transferred to HTF

So, the thermal efficiency is:
Thermal energy absorbed / Thermal energy absorbed by receiver (before thermal losses)

Note that the 'collector average optical efficiency' does not consider losses due to the cosine effect and will be modified in the next version of SAM to include it.

Once you have defined the energy terms (total incident thermal energy, thermal energy absorbed by receiver (before thermal losses), and thermal energy absorbed), you can use a spreadsheet to calculate the avereage efficiencies over a given time period by summing and dividing the relative energy terms. For example, the average thermal efficiency for a month would be:

Sum of thermal energy absorbed over month / Sum of thermal energy absorbed by receiver before thermal losses

The attached spreadsheet uses results from the default physical trough case to calculate the thermal energy absorbed by receiver before thermal losses and the thermal efficiency. The spreadsheet also shows the corrected optical efficiency.

Hi,
why it is not xlsx format when i downloaded the attachment? I can't open it. I am a newcomer of SAM.
And I downloaded a SAM model attached in this forum, it can't be opened neither. Why this happening. Shouldn't it be .zsam format?
Who can help me? I wanna learn to use SAM.

Many thanks in advance!

The two files that are attachments to this discussion are .xlsx files. They were generated by exporting data from SAM's data tables on the Results page to Excel, and then adding Excel formulas to the spreadsheets to calculate values based on the exported data.

You are correct that SAM files are saved as .zsam files. When you export data from SAM to Excel, depending on the version of Excel installed on your computer, you can either save the files as .xls or .xlsx files.

Best regards,
Paul.

Hi Paul,

I am confused with the calculation of annual average and peak solar to electric conversion efficiency for tower and trough systems.

Could you tell me how to do that.?