///////////////////////////////////////////// // HEADER FILE for SPA.C // // // // Solar Position Algorithm (SPA) // // for // // Solar Radiation Application // // // // May 12, 2003 // // // // Filename: SPA.H // // // // Afshin Michael Andreas // // afshin_andreas@nrel.gov (303)384-6383 // // // // Measurement & Instrumentation Team // // Solar Radiation Research Laboratory // // National Renewable Energy Laboratory // // 1617 Cole Blvd, Golden, CO 80401 // ///////////////////////////////////////////// //////////////////////////////////////////////////////////////////////// // // // Usage: // // // // 1) In calling program, include this header file, // // by adding this line to the top of file: // // #include "spa.h" // // // // 2) In calling program, declare the SPA structure: // // spa_data spa; // // // // 3) Enter the required input values into SPA structure // // (input values listed in comments below) // // // // 4) Call the SPA calculate function and pass the SPA structure // // (prototype is declared at the end of this header file): // // spa_calculate(&spa); // // // // Selected output values (listed in comments below) will be // // computed and returned in the passed SPA structure. Output // // will based on function code selected from enumeration below. // // // // Note: A non-zero return code from spa_calculate() indicates that // // one of the input values did not pass simple bounds tests. // // The valid input ranges and return error codes are also // // listed below. // // // //////////////////////////////////////////////////////////////////////// #ifndef __solar_position_algorithm_header #define __solar_position_algorithm_header //enumeration for function codes to select desired final outputs from SPA enum { SPA_ZA, //calculate zenith and azimuth SPA_ZA_INC, //calculate zenith, azimuth, and incidence SPA_ZA_RTS, //calculate zenith, azimuth, and sun rise/transit/set values SPA_ALL, //calculate all SPA output values }; typedef struct { //----------------------INPUT VALUES------------------------ int year; // 4-digit year, valid range: -2000 to 6000, error code: 1 int month; // 2-digit month, valid range: 1 to 12, error code: 2 int day; // 2-digit day, valid range: 1 to 31, error code: 3 int hour; // Observer local hour, valid range: 0 to 24, error code: 4 int minute; // Observer local minute, valid range: 0 to 59, error code: 5 int second; // Observer local second, valid range: 0 to 59, error code: 6 double delta_t; // Difference between earth rotation time and terrestrial time // It is derived from observation only and is reported in this // bulletin: http://maia.usno.navy.mil/ser7/ser7.dat, // where delta_t = 32.184 + (TAI-UTC) + DUT1 // valid range: -8000 to 8000 seconds, error code: 7 double timezone; // Observer time zone (negative west of Greenwich) // valid range: -12 to 12 hours, error code: 8 double longitude; // Observer longitude (negative west of Greenwich) // valid range: -180 to 180 degrees, error code: 9 double latitude; // Observer latitude (negative south of equator) // valid range: -90 to 90 degrees, error code: 10 double elevation; // Observer elevation [meters] // valid range: -6500000 or higher meters, error code: 11 double pressure; // Annual average local pressure [millibars] // valid range: 0 to 5000 millibars, error code: 12 double temperature; // Annual average local temperature [degrees Celsius] // valid range: -273 to 6000 degrees Celsius, error code; 13 double slope; // Surface slope (measured from the horizontal plane) // valid range: -360 to 360 degrees, error code: 14 double azm_rotation; // Surface azimuth rotation (measured from south to projection of // surface normal on horizontal plane, negative west) // valid range: -360 to 360 degrees, error code: 15 double atmos_refract;// Atmospheric refraction at sunrise and sunset (0.5667 deg is typical) // valid range: -5 to 5 degrees, error code: 16 int function; // Switch to choose functions for desired output (from enumeration) //-----------------Intermediate OUTPUT VALUES-------------------- double jd; //Julian day double jc; //Julian century double jde; //Julian ephemeris day double jce; //Julian ephemeris century double jme; //Julian ephemeris millennium double l; //earth heliocentric longitude [degrees] double b; //earth heliocentric latitude [degrees] double r; //earth radius vector [Astronomical Units, AU] double theta; //geocentric longitude [degrees] double beta; //geocentric latitude [degrees] double x0; //mean elongation (moon-sun) [degrees] double x1; //mean anomaly (sun) [degrees] double x2; //mean anomaly (moon) [degrees] double x3; //argument latitude (moon) [degrees] double x4; //ascending longitude (moon) [degrees] double del_psi; //nutation longitude [degrees] double del_epsilon; //nutation obliquity [degrees] double epsilon0; //ecliptic mean obliquity [arc seconds] double epsilon; //ecliptic true obliquity [degrees] double del_tau; //aberration correction [degrees] double lamda; //apparent sun longitude [degrees] double nu0; //Greenwich mean sidereal time [degrees] double nu; //Greenwich sidereal time [degrees] double alpha; //geocentric sun right ascension [degrees] double delta; //geocentric sun declination [degrees] double h; //observer hour angle [degrees] double xi; //sun equatorial horizontal parallax [degrees] double del_alpha; //sun right ascension parallax [degrees] double delta_prime; //topocentric sun declination [degrees] double alpha_prime; //topocentric sun right ascension [degrees] double h_prime; //topocentric local hour angle [degrees] double e0; //topocentric elevation angle (uncorrected) [degrees] double del_e; //atmospheric refraction correction [degrees] double e; //topocentric elevation angle (corrected) [degrees] double eot; //equation of time [minutes] double srha; //sunrise hour angle [degrees] double ssha; //sunset hour angle [degrees] double sta; //sun transit altitude [degrees] //---------------------Final OUTPUT VALUES------------------------ double zenith; //topocentric zenith angle [degrees] double azimuth180; //topocentric azimuth angle (westward from south) [-180 to 180 degrees] double azimuth; //topocentric azimuth angle (eastward from north) [ 0 to 360 degrees] double incidence; //surface incidence angle [degrees] double suntransit; //local sun transit time (or solar noon) [fractional hour] double sunrise; //local sunrise time (+/- 30 seconds) [fractional hour] double sunset; //local sunset time (+/- 30 seconds) [fractional hour] } spa_data; //Calculate SPA output values (in structure) based on input values passed in structure int spa_calculate(spa_data *spa); #endif