# How the albedo is added to the POA inclination ?

## Recommended Posts

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 ?

Best regards,

Loic

##### Share on other sites

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.

##### Share on other sites

• 2 weeks later...

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