Bi-facial Modules - View Factor for Rear Side

[Rafael Santos]

Hi,

I recentrly ran a simulation using a bi-facial module, and I was trying to understand better the physics and results of it.

I came across a loss value of -78,82% for the parameter "View Factor for Rear Side" as shown in the loss diagram attached.

My question is how It came to this number, since my absolute results were:

- Global incident on ground: 1581 kWh/m²;

- Ground reflexion loss: 1265 kWh/m² (this value is ok, 80% loss due to an albedo of 0.2);

- View Factor for the rear side: 749 kWh/m² (this is strange, because I understand it is supposed to be (1581-1265)*0.7882)

Is it something I am doing wrong?

Best regards,

Rafael

Loss Results

Loss Diagram

[Rafael Santos]

Updating:

I did some reverse engineering, and found that with the loss value of 115.95 kWh/m² (36.36%) everything work fine, including all the other losses!

Maybe there is something wrong with the values on the "View Factor for Rear Side" losses presented on the table?

Regards,

Rafael

[André Mermoud]

Perhaps it will useful to read the help "Project design > Bifacial Systems". Everything is explaned in detail here.

Namely the View factor gain (geometric calculation) should be thought as an Energy transfer. When passing to irradiances, it should be renormalized with 1/GCR.