Interval midpoint

Method

Every timestep is evaluated at its middle, whether or not the sun is above the horizon for the whole interval. A timestep whose middle falls before sunrise or after sunset counts as dark and receives no plane irradiance, unless the dark-interval option places its diffuse light on the plane.

Example: the 07:00 row on a day with sunrise at 07:40. The sun is placed at 07:30, before sunrise, so the row counts as dark even though the file holds twenty minutes of sunlight.

For the 12:00 row the sun is placed at 12:30.

The PVWatts path uses this option for every weather file. With a TMY2 or TMY3 file PVWatts places the sun at the middle of the sunlit part in the sunrise and sunset hours; to match it on such a file, choose Sunlit-slice midpoint after applying the path.

The math

$$t_{eval} = \tfrac{1}{2}(t_0 + t_1) \tag{1}$$

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

API

site.sun_timing = interval_midpoint

Symbols follow the symbol registry.