pvlib.solarposition.nrel_earthsun_distance(time, how='numpy', delta_t=67.0, numthreads=4)[source]

Calculates the distance from the earth to the sun using the NREL SPA algorithm described in 1.

  • time (pd.DatetimeIndex) –

  • how (str, optional, default 'numpy') – Options are ‘numpy’ or ‘numba’. If numba >= 0.17.0 is installed, how=’numba’ will compile the spa functions to machine code and run them multithreaded.

  • delta_t (float, optional, default 67.0) – If delta_t is None, uses spa.calculate_deltat using time.year and time.month from pandas.DatetimeIndex. For most simulations specifing delta_t is sufficient. Difference between terrestrial time and UT1. Note: delta_t = None will break code using nrel_numba, this will be fixed in a future version. By default, use USNO historical data and predictions

  • numthreads (int, optional, default 4) – Number of threads to use if how == ‘numba’.


dist (pd.Series) – Earth-sun distance in AU.



Reda, I., Andreas, A., 2003. Solar position algorithm for solar radiation applications. Technical report: NREL/TP-560- 34302. Golden, USA, http://www.nrel.gov.