Model step
Solar position
Sun position at each timestep
Inputs used: Latitude, Longitude, Time zone, Altitude, Step, Station pressure, Ambient temperature
What it is
The solar position step computes where the sun is at every timestep: its height above the horizon and its compass direction. Every later angle depends on it, such as the incidence angle on the module plane and the shadow of one row on the next. The simplified ephemeris takes the declination once per day and differs from the full Solar Position Algorithm by up to about 0.3°, about 0.1° on average over a year; the Astronomical Almanac algorithm stays within about 0.01° of it. The SSC application of the Solar Position Algorithm stays within about 0.005° of it. It reads the weather's pressure and temperature for the refraction. It lights the timesteps by its own sunrise and sunset.
Options
- PVsyst 8 ephemeris: a simplified ephemeris with the USNO declination and a Fourier equation of time
- NREL SPA: NREL's Solar Position Algorithm, accurate to 0.0003°
- Michalsky 1988: the Astronomical Almanac's approximate algorithm, accurate to 0.01°
- NREL SPA (SSC application): NREL's Solar Position Algorithm with SG2 terms, the weather's pressure and temperature, sunrise and sunset at −0.8333°
References
- Reda & Andreas 2008, Solar Position Algorithm for Solar Radiation Applications, NREL/TP-560-34302
- Michalsky 1988, The Astronomical Almanac's algorithm for approximate solar position (1950–2050), Solar Energy 40(3) 227–235
- Blanc & Wald 2012, The SG2 algorithm for a fast and accurate computation of the position of the Sun for multi-decadal time period, Solar Energy 86(10) 3072–3083
API
site.sun_model = pvsyst | spa | michalsky | spa_ssc