# Calculation of Ground Reflection (Albedo)

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Hei.

I am trying to simulate a facade system in Norway based on real irradiation values and compare the simulation to the real system output. While the simulation is relatively accurate in summer the output in winter is very low. This is also the case if I simulate with an albedo of 90% during the winter months.

According to our irradiation sensors on the facade, the real received irradiation is up to 3-4 x GHI during the winter months.
If I look at the formula used to calculate the gains from the ground reflection the maximum possible gain for a facade is
RTI = GHI*albedo/2           (the cos() term will be 0 as ym 90deg)

I have two questions now:

1. What happens with the other 50% of GHI in the theoretical case the albedo is 100%
2. Is there a way to include reflection from the surrounding area (buildings, trees, horizon, etc) into account as well?

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Hei Thomas,

the 50% come from the view factor approach that is used in this model. In short, you have to determine how much of the reflected irradiance of surface A1 can reach surface A2, if we assume that the irradiance is evenly distributed and that the irradiance reflects from the ground evenly in all directions. You can read a more detailed description here:

ad 2) No, sorry. These objects do only serve as shadowing obstacles in PV*SOL, not as sources of reflected light, I am afraid.

Kind regards,

Martin

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