Ground Clearance Height

For fixed tilt systems - is the "ground clearance height" value measured from top of grade to the bottom/lowest edge of the module?

Hi Andrew,

The ground clearance height is an input for bifacial modules on the Module input page.

For fixed arrays with no tracking, the ground clearance height is the distance between the ground and the bottom edge of modules closest to the ground. For arrays with one-axis tracking, the ground clearance height is the distance between the ground and back of modules when the modules are horizontal to the ground.

Best regards,
Paul.

Can SAM model the Ground Clearance for fixed mono facial PV panels say 300 mm above the ground from the low side?
And if so, how can this be done?

Thanks
Claud

Hi Claud,

The ground clearance height is an input on SAM's Module page that only applies to bifacial modules. It is disabled for mono-facial modules:



Best regards,
Paul.
 

Hi Paul,

If the Ground Clearance Height is disabled for monofacial modules, does that mean it does not have an effect to the systems if I enable it momentarily to change the default value and disable it again before simulating a monofacial system?

Additionally, I am aiming to observe the effect(s) of different albedo values on monfacial and bifacial modules. According to literature, albedo affects the height and tilt angle (among other things) of both systems, so I want to find the height and tilt angle where they can have the most output using parametric simulations before using those values in another simulation to get other results. However, as you have said, the Ground Clearance Height is only enabled for bifacial modules. Thus, I would like to know if there are any assumptions or a default height from the ground used in SAM regarding the Ground Clearance Height of monofacial systems. I scanned the  Photovoltaic Model Technical Reference Update but I can't seem to find an exact height/number. Thanks!


Best regards,
Andrea

Hi Andrea,

In the internal code for the Detailed PV model, the ground clearance height is used in the 'calc_rear_side' function , which only gets called for bifacial modules. If you clear the Module is bifacial checkbox on the Module page in SAM, that function never gets called. So, yes, if you switch to bifacial mode, change the ground clearance height, and then switch back to monofacial mode, SAM does not use the ground clearance height for irradiance calculations.

For bifacial modules, SAM calculates the irradiance that reflects on the rear of the module, accounting for shadows caused by the modules, which requires the ground clearance value.

For monofacial modules, the ground reflectance is treated as uniform, and is not affected by ground clearance, as described in Section 6.4 of the PV reference manual, Gilman, P.; Dobos, A.; DiOrio, N.; Freeman, J.; Janzou, S.; Ryberg, D. (2018) SAM Photovoltaic Model Technical Reference Update. 93 pp.; NREL/TP-6A20-67399. ( PDF 1.8 MB ).

Note that we wrote the reference manual before SAM could model bifacial modules. For documentation of SAM's bifacial model, see the references listed under "Bifacial Modules" on the PV Publications page:  sam.nrel.gov/photovoltaic/pv-publications.html .

Best regards,
Paul.