How the albedo is added to the POA inclination ?

[LoicA]

Hi,

I am wondering how the albedo value is used by the process of POA irradiation calculation.

Let's say we have 1000W/m² GHI. The albedo value is 0.2. Then, is the transposition process use 1000W/m² x (1+0.2) to determine the POA irradiation ?

Thank you for your answer.

Best regards,

Loic

[André Mermoud]

The albedo is computed by the transposition model, in the same way for each model.

Please see the description of the Hay model in the Help "Physical models used > Irradiation models > The Hay transposition model"

The Albedo component is the irradiance reflected by the ground "seen" by the plane :

AlbInc = ρ * GlobHor * (1 - cos i) / 2

where i = tilt angle. With horizontal plane (i=0), the albedo contribution is null of course.

For a"normally" tilted plane, for ex. cos(25°) = 0.906, the contribution is 0.046; for a vertical plane, it is 0.5.

[LoicA]

Dear Mr Mermoud thank you for the answer,

Ok it's more clear now.

If I am right, GlobHor = BeamHor + DiffHor

So

Albinc = rho * (BeamHor + DiffHor) * (1 - cos i) /2 ?

Regarding your explanation in "Physical models used > Irradiation models > The Hay transposition model", the calculation of the POA irradiation does not seem that much difficult.

POA irrad = BeamInc + DiffInc + AlbInc = we have all the constants and variables needed

I will read more stuff or try to work on the hourly PVsyst result to be more confident on this topic.

Thanks, Loic