You can provide your own data for horizon information as described here, but as comma separated list instead of a file.
In the horizon=… parameter each number representing the horizon height in degrees in a certain compass direction around the point of interest. The horizon height cannot be higher than 90 degrees.
The horizon heights must be given in a clockwise direction starting at North; that is, from North, going to East, South, West, and back to North. The values are assumed to represent equal angular distance around the horizon. For instance, if you have 36 values in the list, PVGIS assumes that the first point is due north, the next is 10 degrees east of north, and so on, until the last point, 10 degrees west of north.
In order to have a relevant influence on the result, at least 12 values should be specified, which corresponds to a resolution of 30°.
For instance, if you have 36 values, PVGIS assumes that the first point is due north, the next is 10 degrees east of north, and so on, until the last point, 10 degrees west of north.
To illustrate this, here are 3 examples from PVGIS, once without horizon, 4 values and 12 values, each simulating shading with 60° horizon in the south.
If you look closely, you will see that
- the diffuse component is almost unchanged
- the direct component is influenced
(Location in Germany, day in June, declination 35°, orientation south)
No horizon
4 values
0,30,60,30
12 values
0,0,15,30,45,60,60,60,45,30,15,0