SAM generates heliostat fields asymmetric regarding north-south axis

Hi Paul,
I found that heliostat fields generated by SAM 2014.11.24 are often asymmetric with respect to the north-south axis. I generated a field for the southern hemisphere with ~22'000 heliostats, each having a reflective area of ~50m². Tower height ~190m, Latitude

Any suggestions why this happens and how it can be avoided?


Kind regards

Gary

P.S.: As a work around, I exported the field, rotated it by about 6° to (almost) establish symmetry with respect to the north-south axis, and re-imported the field. This improved field efficiency only slightly, but improved plausibility of the field layout a lot :-)

Hi Gary,

I'm the developer of the new tower model, so Paul pointed me to your question. The model determines the best plant layout by simulating performance of the field using real weather data, and often it is the case that particular sites have weather that is more favorable in the morning or afternoon because of local weather patterns. In these cases, the optimal layout is "tilted" to capture more energy during times when more sunlight is typically available.

This is the intention of the model, although we shouldn't rule out that there may also be a problem with the weather file or with the model itself. One way to determine whether this behavior makes sense is to view the weather data using SAM's plotting tools. If the monthly profiles tend to favor energy production asymmetrically about solar noon, then the field should typically align in a corresponding way.

Mike Wagner
NREL

Hi Mike,

Thank you very much for the quick and positive response: I am happy to learn that the model considers asymmetric weather conditions for optimization. That's more than I expected. Great!
Best regards

Gary
P.S.: Will double-check weather data file, just in case...