Welcome to solpos documentation!¶

This is a thin wrapper around NREL’s SOLPOS 2.0, exposing the S_solpos C-function to python as solpos.solpos(). All possible outputs are calculated, and exposed via the solpos.SolposResult() NamedTuple-object, so they can be accessed as an attribute.

NREL’s description:

NREL’s Solar Position and Intensity (SOLPOS 2.0) C function calculates the apparent solar position and intensity (theoretical maximum solar energy) based on date, time, and location on Earth.

solpos on GitHub: https://github.com/jkittner/solpos
NREL’s SOLPOS 2.0: https://www.nrel.gov/grid/solar-resource/solpos.html
NREL’s Disclaimer: https://www.nrel.gov/disclaimer.html

Contents¶

solpos
- solpos()
- SolposResult

Installation¶

To install solpos, open an interactive shell and run

pip install solpos

Gettings Started¶

from solpos import solpos

result = solpos(
    year=2022,
    month=10,
    day=27,
    hour=16,
    minute=26,
    second=0,
    timezone=2,
    latitude=51.44579,
    longitude=7.26274,
)
# solar elevation angle refracted
print(result.elevref)
# solar declination
print(result.declin)
# shadow band correction factor
print(result.sbcf)

13.568160057067871
-12.900684356689453
1.093388319015503

For a detailed description of all (calculated) attributes see: solpos.SolposResult().

Accuracy¶

The python version wrapping the C-function is tested for accuracy against running the pure C-version and NREL’s SOLPOS online calculator

against the online calculator: \(\pm 1 * 10^{-4}\)
against the pure C-Version: \(\pm 1 * 10^{-6}\)

License¶

The project is licesned under the MIT License and vendors SOLPOS 2.0 via SolarPILOT which is licensed under a mixed MIT and GPLv3 license and […] allows for-profit and not-for-profit organizations to develop and redistribute software based on SolarPILOT under terms of an MIT license.

References¶

SolarPILOT

Wagner, M.J. (2018). “SolarPILOT Open-Source Software Project: https://github.com/NREL/SolarPILOT/tree/21a1466398ec22db24a5a838e5133da58e347b83.” Accessed (27/10/2022). National Renewable Energy Laboratory, Golden, Colorado.

Astronomical Solar Position

Michalsky, J. 1988. The Astronomical Almanac’s algorithm for approximate solar position (1950-2050). Solar Energy 40 (3), 227-235.

Michalsky, J. 1988. ERRATA: The astronomical almanac’s algorithm for approximate solar position (1950-2050). Solar Energy 41 (1), 113.

Distance from Sun to Earth

Spencer, J. W. 1971. Fourier series representation of the position of the sun. Search 2 (5), 172. NOTE: This paper gives solar position algorithms as well, but the Michalsky/Almanac algorithm above is more accurate.

Atmospheric Refraction Correction

Zimmerman, John C. 1981. Sun-pointing programs and their accuracy. SAND81-0761, Experimental Systems Operation Division 4721, Sandia National Laboratories, Albuquerque, NM.

Shadow Band Correction Factor

Drummond, A. J. 1956. A contribution to absolute pyrheliometry. Q. J. R. Meteorol.2 Soc. 82, 481-493.

Relative Optical Air Mass

Kasten, F. and Young, A. 1989. Revised optical air mass tables and approximation formula. Applied Optics 28 (22), 4735-4738.

Renormalization of KT (“PRIME”)

Perez, R., P. Ineichen, Seals, R., & Zelenka, A. 1990. Making full use of the clearness index for parameterizing hourly insolation conditions. Solar Energy 45 (2), 111-114.

Solar Position Relative to Earth

Iqbal, M. 1983. An Introduction to Solar Radiation. Academic Press, NY.