Converting solar irradiance on tilted surface to solar irradiance data on horizontal

[Philip9]

I've got the data for solar irradiance on a tilted surface and I want to convert it back to horizontal global irradiance. I've tried the toool transposition factor, by obtaining the tilt factor to convert the solar irradiance on tilted surface to solar irradiance data on horizontal. However, it doesn't work and I don't know why. Anyone could help me?

[Bruno Wittmer]

Transforming the solar irradiance from the tilted plane (POA) back to the horizontal is a non-trivial problem, involving some modelling.

If you have POA values that you want to use, the way to go is to import them through 'Databases -> Import ASCII meteo file' (check the online help and tutorial for instructions).

This will do the transformation back to the horizontal plane, but be careful with some pitfalls described in the following two FAQ entries:

Can I import POA measurements ?

My transposed POA values don't match the imported values

[dtarin]

Hello,

I have a system with multiple orientations but only one sensor mounted for one orientation collecting POA irradiance at a one minute interval. Is it possible to use this POA irradiance to calculate GHI, and then use this GHI to calculate POA for other orientations? Or can I convert directly from one POA to another?