SolTrack: a free, fast and accurate routine to compute the position of the Sun

Abstract: We present a simple, free, fast and accurate C/C++ and Python routine called SolTrack, which can compute the position of the Sun at any instant and any location on Earth. The code allows tracking of the Sun using a low-specs embedded processor, such as a PLC or a microcontroller, and can be used for applications in the field of (highly) concentrated (photovoltaic) solar power ((H)CPV and CSP), such as tracking control and yield modelling. SolTrack is accurate, fast and open in its use, and compares favourably with similar algorithms that are currently available for solar tracking and modelling. SolTrack computes $1.5 \times 10<sup>6$ positions per second on a single 2.67GHz CPU core. For the period between the years 2017 and 2116 the uncertainty in position is $0.0036 \pm 0.0042<sup>\circ$, that in solar distance 0.0017 $\pm$ 0.0029%. In addition, SolTrack computes rise, transit and set times to an accuracy better than 1 second. The code is freely available online (http://soltrack.sf.net, https://pypi.org/project/soltrack/).