PV sunpath shading component issue with results

#1

Hi @djordje,

I have a question on the Ladybug_Sunpath Shading component. I am running a shaded analysis considering only the tested PV panel as context. I have noticed that the AC Energy per Year reduces between unshaded and shaded analysis when considering tilted panels which are not facing 180 degrees due south. As you can see from the images below, this doesn’t occur for south-facing panels. I have noticed that the greater is the inclination and rotation of the panel, the higher is the annual shading and therefore the AC energy reduction. Given that the panel is unobstructed in both options, the AC per year should not be the same before and after the Sunpath Shading analysis regardless of the orientation and the inclination?

#2

Hi @mikim4,

Tilt angle of the PVsurface is important, as it determines the amount of irradiance that this surface ‘receives’.
It is also important for the (self)shading: as you have concluded it yourself, the higher the tilt angle, the more sunpath window it shades (this is shading from the panel itself - its back side). But, the crucial thing is: which part of the sunpath diagram does it shade!
When the North is at 0 degrees, very small amounts of sunpath window are shaded.
When North is around 315 (as in your screenshot) the shading is a bit larger (sunpath quandrants with higher radiation percent are more affected) as the sunpath window is rotated.
Did that answer your question, or did I misunderstand you?

#3

Hi @djordje,

Thank you for your answer, the way the shading component works makes perfect sense to me. However, I am still a bit confused about this topic. I would have thought that selfshading and any performance reduction due to orientation and inclination of the panel were already taken into account by the component based on the PVWatt software. If this is not the case, am I correct in assuming that, in order to get more accurate results, the Ladybug_Shading Component should be run for all type of scenarios, even when there is no context to shade the panel apart from itself?

#4

Hi Michela,
@mikim4

PVWatts does account for performance reduction/increase due to change of the tilt and orientation angles.
But not from the self-shading “created” due to tilt/orientation angles change.
This needs to be done through annualShading_ input of the “DC to AC derate factor” component (it essentially calculates the losses of all types, shading being one of them).

If this is not the case, am I correct in assuming that, in order to get more accurate results, the Ladybug_Shading Component should be run for all type of scenarios, even when there is no context to shade the panel apart from itself?

Which all types of scenarios? Can you clarify this?

The more detailed you model the surroundings of the PV panel(s) (neighbor buildings, structures, terrain) and use them as inputs for the “Sunpath shading” component, the more detailed the shading analysis will be, and therefor the final AC output as well.

Gismo, Elk and Heron try to overcome some of these surroundings requirements:

Did I misunderstood your question?

#5

Hi @djordje,
Thank you very much for your reply.
I think my confusion originated as I thought self-shading was already considered in the PVWatt component.
As this aspect is not considered in the LV_photovoltaic surface, in case I want to compare the performance of a PV panel with and without obstructions do you think running the LB_Sunpath Shading component in both scenarios to take into account of self-shading in all options would be the right approach?

Michela

#6

Hi @mikim4,
You can do that. Bear in mind that you do not have to input your “PVsurface" into the "context” input of the “Sunpath shading” component. This will be automatically done by the component.
If I haven’t answered your question, or you have others, please be free to post it.