Sunlit-slice midpoint

Method

In a timestep that contains a sunrise or a sunset, the sun is above the horizon for only part of the interval. This rule places the sun at the middle of that lit part, rounded to the whole minute. Every other timestep is evaluated at its middle. The irradiance of the file, an average over the whole interval, is then converted with the geometry of the time the light actually arrived.

Example: the 07:00 row on a day with sunrise at 07:40. The lit part runs from 07:40 to 08:00 and the sun is placed at 07:50.

For the 12:00 row the lit part is the whole hour and the sun is placed at 12:30.

The math

$$t_{eval} = \tfrac{1}{2}\big(\max(t_0, t_{rise}) + \min(t_1, t_{set})\big) \tag{1}$$

where

Symbol	Meaning	Unit
$t_{eval}$	the instant at which the sun position is evaluated, local standard time	h
$t_0, t_1$	the start and end of the timestep, local standard time	h
$t_{rise}, t_{set}$	the sunrise and sunset times of the day, local standard time	h

References

1. PVsyst 8 help, Solar geometry and time definition
2. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.

API

site.sun_timing = sunlit_midpoint

Symbols follow the symbol registry.