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I have some questions about the relation between Global Horizontal Irradiation and Global Incident in coll. Plane in loss diagram.

Normally to get energy, we shoul know GlobInc value and that value is come from Global Horizontal Irradiance. Then this value seems to be increased in normal case.

So, to understand the principle, I found some base formula to calculate GlobInc from GlobHor as follows.

Global incident in coll. Plane(GlobInc) = GlobHor x sin(α+β)/sinα

α(elevation angle of sun) = 90 – φ + δ

φ = Latitude

δ = angle of inclination = 23.45° x sin[(360/365) x (284 +d)}

β = tilted angle of panel

According to the above formula, δ might be calculated as 0 at average annually and applying the remaining input, calculated result should have been matched or close to be matched.

However, the result is highly different from what I expect.

So, I would like to ask you to clarify that the formula which I found out is not correct or could you provide some help to make simple calculation model using MS excel or explain the principle why normally GlobInc value is higher than GlobHor.

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• 2 weeks later...
It depends on the transposition model you have selected for your simulation. The Perez transposition model is the default for PVsyst, and that is where you will find the formula for converting GHI to POA