Seemingly inconsistent results with dual axis systems as compared to fixed axis

Hi, I've been doing a number of dual axis tracking projects and I recently came to the realization that results for dual axis tracking vary on more than just weather and inverter efficiency. Running two models of different size with the same inverter efficiency and weather files but different modules and system sizes yielded a difference of nearly 10% increase from the fixed solar equivalent.

The standard for the system we're looking at (All Earth L20 Trackers in Oregon) is a 40% increase, however SAM often shows as much as 50% increase in efficiency. Since this does not match our experience in the field, we're looking for a way to confirm and justify these differences. We're attempting to find the formulas or comparative data to confirm SAM's results.

Thank you,
Jesse Sharpe
Sharpe Energy Solutions

Dear Jesse,

You may be interested in some of the comparison studies we have done, which are presented on the Case Studies and Validation page of this website:

sam.nrel.gov/case-studies

Are you seeing the 50% increase over the entire year or for specific time steps? When you say that you expect a 40% increase, is that an annual increase?

You might want to look at the "clipping losses" that SAM reports to see if that is contributing to the differences. SAM limits the array output to the inverter's rated power, so if the array is over-sized, SAM will report lower output compared to a system with a larger inverter.

Without seeing specific files, it is hard for me to say what might be causing the differences.

Best regards,
Paul.