solar angles calculation. More...

Functions
int	S_date (void)
	Returns date. This function calculates the month and day of month, given the day number (number of day in year, sometimes confusingly called the "Julian Day", but I know that you will never call it that). Requires: Year and day number: S_year NOTE: 2-digit year "xx" is assumed "19xx" DEFAULT S_year = 2001 S_daynum RANGE: -1 to a large positive integer . More...

int	S_solpos (void)
	Returns ..... This function calculates the apparent solar position and intensity (theoretical maximum solar energy) based on the date, time, and location on Earth. Requires: Date and time: S_year DEFAULT 2001 S_month S_day S_hour DEFAULT 12 S_minute DEFAULT 0 S_second DEFAULT 0 Location: S_latitude S_longitude Location/time adjuster: S_timezone Atmospheric pressure and temperature: S_press DEFAULT 1013.0 mb S_temp DEFAULT 10.0 degrees C Tilt of flat surface that receives solar energy: S_aspect DEFAULT 180 (South) S_tilt DEFAULT 0 (Horizontal) . More...

Variables
double	S_amass
	O: Relative optical airmass. More...

double	S_ampress
	O: Pressure-corrected airmass. More...

double	S_aspect

double	S_azim
	O: Solar azimuth angle: N=0, E=90, S=180, W=270. More...

double	S_cosinc
	O: Cosine of solar incidence angle on panel. More...

int	S_day
	I/O: Day of month (May 27 = 27, etc.) I/O: Day of month (May 27 = 27, etc.) S_solpos needs this, but S_date will calculate it from S_daynum. More...

double	S_dayang
	T: Day angle (daynum*360/year-length) degrees. More...

int	S_daynum
	I/O: Day number (day of year; Feb 1 = 32 ) I/O: Day number (day of year; Feb 1 = 32 ) S_date needs this, but S_solpos will calculate it from S_month and S_day. More...

double	S_declin

double	S_eclong
	T: Ecliptic longitude, degrees */. More...

double	S_ecobli
	T: Obliquity of ecliptic */. More...

double	S_ectime
	T: Time of ecliptic calculations */. More...

double	S_elevref

*double	S_eqntim
	T: Equation of time (TST - LMT), minutes */. More...

double	S_erv

*double	S_etr

*double	S_etrn

*double	S_etrtilt

*double	S_gmst
	T: Greenwich mean sidereal time, hours */. More...

int	S_hour
	I: Hour of day, 0 - 23, DEFAULT = 12 I: Hour of day, 0 - 23, DEFAULT = 12. More...

double	S_hrang

*double	S_julday

*double	S_latitude
	I: Latitude, degrees north (south negative) */. More...

double	S_lmst
	T: Local mean sidereal time, degrees */. More...

double	S_longitude
	I: Longitude, degrees east (west negative) */. More...

int	S_minute
	I: Minute of hour, 0 - 59, DEFAULT = 0 I: Minute of hour, 0 - 59, DEFAULT = 0. More...

double	S_mnanom
	T: Mean anomaly, degrees */. More...

double	S_mnlong
	T: Mean longitude, degrees */. More...

int	S_month
	I/O: Month number (Jan = 1, Feb = 2, etc.) I/O: Month number (Jan = 1, Feb = 2, etc.) S_solpos needs this, but S_date will calculate it from S_daynum. More...

double	S_press

*double	S_prime
	O: Factor that normalizes Kt, Kn, etc. */. More...

double	S_rascen
	T: Right ascension, degrees */. More...

double	S_sbcf
	O: Shadow-band correction factor */. More...

int	S_second
	I: Second of minute, 0 - 59, DEFAULT = 0 I: Second of minute, 0 - 59, DEFAULT = 0. More...

double	S_solcon
	T: Solar constant, 1367 W/sq m */. More...

double	S_ssha
	T: Sunset(/rise) hour angle, degrees */. More...

double	S_sunrise

*double	S_sunset

*double	S_temp

*double	S_tilt
	I: Degrees tilt from horizontal of panel */. More...

double	S_timezone

*double	S_tst
	T: True solar time, minutes from midnight */. More...

double	S_tstfix
	T: True solar time - local standard time */. More...

double	S_unprime
	O: Factor that denormalizes Kt', Kn', etc. */. More...

double	S_utime
	T: Universal (Greenwich) standard time */. More...

int	S_year
	I: 4-digit year (2-digit is assumed 19xx) I: 4-digit year (2-digit is assumed 19xx) DEFAULT = 2001. More...

double	S_zenetr

*double	S_zenref

Detailed Description

solar angles calculation.

Author: Daniele Bortoli

Definition in file SOLPOS.H.

Function Documentation

§ S_date()

*extern int S_date ( void )

Returns date.
This function calculates the month and day of month, given the day number (number of day in year, sometimes confusingly called the "Julian Day", but I know that you will never call it that).
Requires:
Year and day number:
S_year NOTE: 2-digit year "xx" is assumed "19xx" DEFAULT S_year = 2001
S_daynum RANGE: -1 to a large positive integer
.

Returns: : Year, month, day ( S_year, S_month, S_day)

Definition at line 166 of file SOLPOS.C.

References imon, leap, lenyr, month_days, ndy, S_day, S_daynum, S_month, and S_year.

Referenced by SZACalc().

 {
     /* We will allow -1 (in order to adjust to the previous year) but no
 less */
     if ( S_daynum < -1 ) {
         printf ( "S_date => Please fix the day number: %10d\n", S_daynum );
         return ( -1 );
     }
 
     /* If a 2-digit year "xx" is given, assume "19xx" */
     if ( S_year < 100 )
         S_year += 1900;
 
     /* Set the leap year switch */
     if ( ((S_year % 4) == 0) && 
          ( ((S_year % 100) != 0) || ((S_year % 400) == 0) ) )
         leap = 1;
     else
         leap = 0;
 
     /* If S_daynum is a large number, it is in a future year */
     ndy = S_daynum;
     while ( ndy > lenyr[leap] ) {
         ++S_year;
         ndy -= lenyr[leap];
         if ( ((S_year % 4) == 0) && 
              ( ((S_year % 100) != 0) || ((S_year % 400) == 0) ) )
             leap = 1;
         else
             leap = 0;
     }
 
     /* A non-positive day number indicates the previous year */
     if ( ndy <= 0 ) {
         --S_year;
         leap  =  0;
         ndy  += 365;
     }
 
     /* Now that the year is fixed, find the month */
     imon = 12;
     while ( ndy <= month_days [leap][imon] )
         --imon;
 
     /* Set the month and day of month */
     S_month = imon;
     S_day   = ndy - month_days[leap][imon];
 
     return ( 0 );
 }

Here is the caller graph for this function:

§ S_solpos()

int S_solpos ( void )

Returns .....
This function calculates the apparent solar position and intensity (theoretical maximum solar energy) based on the date, time, and location on Earth.
Requires:
Date and time:
S_year DEFAULT 2001
S_month
S_day
S_hour DEFAULT 12
S_minute DEFAULT 0
S_second DEFAULT 0
Location:
S_latitude
S_longitude
Location/time adjuster:
S_timezone
Atmospheric pressure and temperature:
S_press DEFAULT 1013.0 mb
S_temp DEFAULT 10.0 degrees C
Tilt of flat surface that receives solar energy:
S_aspect DEFAULT 180 (South)
S_tilt DEFAULT 0 (Horizontal)
.

Returns: S_amass; Relative optical airmass; S_ampress; Pressure-corrected airmass; S_azim; Solar azimuth angle: N=0, E=90, S=180, W=270; S_cosinc; Cosine of solar incidence angle on panel; S_dayang; Day angle (daynum*360/year-length) degrees; S_declin; Declination–zenith angle of solar noon at equator, degrees NORTH; S_eclong; Ecliptic longitude, degrees; S_ecobli; Obliquity of ecliptic; S_ectime; Time of ecliptic calculations; S_elevref; Solar elevation angle, deg. from horizon, refracted; S_eqntim; Equation of time (TST - LMT), minutes; S_erv; Earth radius vector (multiplied to solar constant); S_etr; Extraterrestrial (top-of-atmosphere) W/sq m global horizontal solar irradiance; S_etrn; Extraterrestrial (top-of-atmosphere) W/sq m direct normal solar irradiance; S_etrtilt; Extraterrestrial (top-of-atmosphere) W/sq m global irradiance on a tilted surface; S_gmst; Greenwich mean sidereal time, hours; S_hrang; Hour angle–hour of sun from solar noon, degrees WEST; S_julday; Julian Day of 1 JAN 2000 minus 2,400,000 days (in order to regain single precision); S_latitude; Latitude, degrees north (south negative); S_longitude; Longitude, degrees east (west negative); S_lmst; Local mean sidereal time, degrees; S_mnanom; Mean anomaly, degrees; S_mnlong; Mean longitude, degrees; S_rascen; Right ascension, degrees; S_press; Surface pressure, millibars, used for refraction correction and S_ampress; S_prime; Factor that normalizes Kt, Kn, etc.; S_sbcf; Shadow-band correction factor; S_solcon; Solar constant, 1367 W/sq m; S_ssha; Sunset(/rise) hour angle, degrees; S_sunrise; Sunrise time, minutes from midnight, local, no refraction; S_sunset; Sunset time, minutes from midnight, local, no refraction; S_temp; Ambient dry-bulb temperature, degrees C, used for refraction correction; S_tilt; Degrees tilt from horizontal of panel; S_timezone; Time zone, east (west negative). USA: Mountain = -7, Central = -6, etc.; S_tst; True solar time, minutes from midnight; S_tstfix; True solar time - local standard time; S_unprime; Factor that denormalizes Kt', Kn', etc.; S_utime; Universal (Greenwich) standard time; S_zenetr; Solar zenith angle, no atmospheric correction (= ETR); S_zenref; Solar zenith angle, deg. from zenith, refracted

Definition at line 246 of file SOLPOS.C.

References bottom, c2, ca, cd, cdcl, ce, cecl, ch, cl, cp, cssha, ct, cz, d2, degrad, delta, elev, leap, month_days, p, prestemp, raddeg, refcor, s2, S_amass, S_ampress, S_aspect, S_azim, S_cosinc, S_day, S_dayang, S_daynum, S_declin, S_eclong, S_ecobli, S_ectime, S_elevref, S_eqntim, S_erv, S_etr, S_etrn, S_etrtilt, S_gmst, S_hour, S_hrang, S_julday, S_latitude, S_lmst, S_longitude, S_minute, S_mnanom, S_mnlong, S_month, S_press, S_prime, S_rascen, S_sbcf, S_second, S_solcon, S_ssha, S_sunrise, S_sunset, S_temp, S_tilt, S_timezone, S_tst, S_tstfix, S_unprime, S_utime, S_year, S_zenetr, S_zenref, sa, sd, se, sl, sp, st, sz, t1, t2, tanelev, and top.

Referenced by SZACalc().

 {
      /* No absurd dates, please. */
     if ( (S_month < 1) || (S_month > 12) )
     {
         printf ( "S_solpos => Please fix the month: %10d\n", S_month );
         return ( -1 );
     }
     else if ( (S_day < 1) || (S_day > 31 ) )
     {
         printf ( "S_solpos => Please fix the day of month: %10d\n", S_day );
         return ( -1 );
     }
 
     /* No absurd times, please. */
     if ( (S_hour < 0) || (S_hour > 23) )
     {
         printf ( "S_solpos => Please fix the hour: %10d\n", S_hour );
         return ( -1 );
     }
     else if ( (S_minute < 0) || (S_minute > 59) )
     {
         printf ( "S_solpos => Please fix the minute: %10d\n", S_minute );
         return ( -1 );
     }
     else if ( (S_second < 0) || (S_second > 59) )
     {
         printf ( "S_solpos => Please fix the second: %10d\n", S_second );
         return ( -1 );
     }
     else if ( (S_timezone < -12.0) || (S_timezone > 12.0) )
     {
         printf ( "S_solpos => Please fix the time zone: %10.4f\n",
 S_timezone );
         return ( -1 );
     }
     /* No absurd locations, please. */
     if ( fabs (S_longitude) > 180.0 ) {
         printf ( "S_solpos => Please fix the longitude: %10.4f\n",
 S_longitude );
         return ( -1 );
     }
     else if ( fabs (S_latitude) > 90.0 ) {
         printf ( "S_solpos => Please fix the latitude: %10.4f\n",
 S_latitude );
         return ( -1 );
     }
 
     /* No silly temperatures or pressures, please. */
     if ( fabs (S_temp) > 100.0 ) {
         printf ( "S_solpos => Please fix the temperature: %10.4f\n", S_temp );
         return ( -1 );
     }
     else if ( (S_press < 0.0) || (S_press > 2000.0) ) {
         printf ( "S_solpos => Please fix the pressure: %10.4f\n", S_press );
         return ( -1 );
     }
 
     /* Day number */
     /* (convert day-of-month to day-of-year (non-leap)) */
     S_daynum = S_day + month_days[0][S_month];
 
     /* (if no year was entered, give it an arbitrary 2001.  Also, turn
         2-digit years into 19xx.  Note that if the year > 1999, it had
         better be 4-digit) */
     if ( S_year < 0 )
         S_year  = 2001;
     else if ( S_year < 100 )
         S_year += 1900;
 
     /* (now adjust for leap year) */
     if ( ((S_year % 4) == 0) &&
        ( ((S_year % 100) != 0) || ((S_year % 400) == 0) ) &&
              (S_month > 2) )
         S_daynum += 1;
 
      /* Day angle */
         /*  Iqbal, M.  1983.  An Introduction to Solar Radiation.
             Academic Press, NY., page 3 */
      S_dayang = 360.0 * ( S_daynum - 1 ) / 365.0;
 
     /* Earth radius vector * solar constant = solar energy */
         /*  Spencer, J. W.  1971.  Fourier series representation of the
 position
             of the sun.  Search 2 (5), page 172 */
     sd     = sin (raddeg * S_dayang);
     cd     = cos (raddeg * S_dayang);
     d2     = 2.0 * S_dayang;
     c2     = cos (raddeg * d2);
     s2     = sin (raddeg * d2);
 
     S_erv  = 1.000110 + 0.034221 * cd + 0.001280 * sd;
     S_erv  += 0.000719 * c2 + 0.000077 * s2;
 
     /* Universal Coordinated (Greenwich standard) time */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_utime = S_hour * 3600.0 + S_minute * 60.0 + S_second;
     S_utime = S_utime / 3600.0 - S_timezone;
 
     /* Julian Day minus 2,400,000 days (to eliminate roundoff errors) */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
 
     delta    = S_year - 1949;
     leap     = (int) ( delta / 4.0 );
     S_julday = 32916.5 + delta * 365.0 + leap + S_daynum + S_utime / 24.0;
 
     if ( ( (S_year % 100) == 0 ) && ( (S_year % 400) != 0) )
         --S_julday;
 
     /* Time used in the calculation of ecliptic coordinates */
     /* Noon 1 JAN 2000 = 2,400,000 + 51,545 days Julian Date */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_ectime = S_julday - 51545.0;
 
     /* Mean longitude */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_mnlong  = 280.460 + 0.9856474 * S_ectime;
 
     /* (dump the multiples of 360, so the answer is between 0 and 360) */
     S_mnlong -= 360.0 * (int) ( S_mnlong / 360.0 );
     if ( S_mnlong < 0.0 )
         S_mnlong += 360.0;
 
     /* Mean anomaly */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_mnanom  = 357.528 + 0.9856003 * S_ectime;
 
     /* (dump the multiples of 360, so the answer is between 0 and 360) */
     S_mnanom -= 360.0 * (int) ( S_mnanom / 360.0 );
     if ( S_mnanom < 0.0 )
         S_mnanom += 360.0;
 
     /* Ecliptic longitude */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_eclong  = S_mnlong + 1.915 * sin ( S_mnanom * raddeg ) +
                     0.020 * sin ( 2.0 * S_mnanom * raddeg );
 
     /* (dump the multiples of 360, so the answer is between 0 and 360) */
     S_eclong -= 360.0 * (int) ( S_eclong / 360.0 );
     if ( S_eclong < 0.0 )
         S_eclong += 360.0;
 
     /* Obliquity of the ecliptic */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_ecobli = 23.439 + 4.0e-07 * S_ectime;
 
     /* Declination */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_declin = degrad * asin ( sin (S_ecobli * raddeg) *
                                sin (S_eclong * raddeg) );
 
     /* Right ascension */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     top      =  cos ( raddeg * S_ecobli ) * sin ( raddeg * S_eclong );
     bottom   =  cos ( raddeg * S_eclong );
 
     S_rascen =  degrad * atan2 ( top, bottom );
 
     /* (make it a positive angle) */
     if ( S_rascen < 0.0 )
         S_rascen += 360.0;
 
     /* Greenwich mean sidereal time */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_gmst  = 6.697375 + 0.0657098242 * S_ectime + S_utime;
 
     /* (dump the multiples of 24, so the answer is between 0 and 24) */
     S_gmst -= 24.0 * (int) ( S_gmst / 24.0 );
     if ( S_gmst < 0.0 )
         S_gmst += 24.0;
 
     /* Local mean sidereal time */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_lmst  = S_gmst * 15.0 + S_longitude;
 
     /* (dump the multiples of 360, so the answer is between 0 and 360) */
     S_lmst -= 360.0 * (int) ( S_lmst / 360.0 );
     if ( S_lmst < 0.)
         S_lmst += 360.0;
 
     /* Hour angle */
         /*  Michalsky, J.  1988.  The Astronomical Almanac's algorithm for
             approximate solar position (1950-2050).  Solar Energy 40 (3),
             pp. 227-235. */
     S_hrang = S_lmst - S_rascen;
 
     /* (force it between -180 and 180 degrees) */
     if ( S_hrang < -180.0 )
         S_hrang += 360.0;
     else if ( S_hrang > 180.0 )
         S_hrang -= 360.0;
 
     /* ETR solar zenith angle */
         /*  Iqbal, M.  1983.  An Introduction to Solar Radiation.
             Academic Press, NY., page 15 */
     cd = cos ( raddeg * S_declin );
     ch = cos ( raddeg * S_hrang );
     cl = cos ( raddeg * S_latitude );
     sd = sin ( raddeg * S_declin );
     sl = sin ( raddeg * S_latitude );
 
     cz = sd * sl + cd * cl * ch;
 
     /* (watch out for the roundoff errors) */
     if ( fabs (cz) > 1.0 ) {
         if ( cz >= 0.0 )
             cz =  1.0;
         else
             cz = -1.0;
     }
 
     S_zenetr   = acos ( cz ) * degrad;
 
     /* (limit the degrees below the horizon to 9 [+90 -> 99]) */
    // if ( S_zenetr > 99.0 )
      //   S_zenetr = 99.0;
 
     /* Sunset hour angle */
     /*  Iqbal, M.  1983.  An Introduction to Solar Radiation.
         Academic Press, NY., page 16 */
     S_ssha  = 90.0;
     cdcl    = cd * cl;
 
     if ( fabs ( cdcl ) >= 0.001 ) {
     cssha = -sl * sd / cdcl;
 
     /* This keeps the cosine from blowing on roundoff */
     if ( cssha < -1.0  )
         S_ssha = 180.0;
     else if ( cssha > 1.0 )
         S_ssha = 0.0;
     else
         S_ssha = degrad * acos ( cssha );
     }
 
     /* Shadowband correction factor */
     /*  Drummond, A. J.  1956.  A contribution to absolute pyrheliometry.
         Q. J. R. Meteorol. Soc. 82, pp. 481-493 */
     p      = 0.1526 * pow (cd,3);
     t1     = sl * sd * S_ssha * raddeg;
     t2     = cl * cd * sin ( S_ssha * raddeg );
     S_sbcf = 0.04 + 1.0 / ( 1.0 - p * ( t1 + t2 ) );
 
     /* TST -> True Solar Time = local standard time + TSTfix */
         /*  Iqbal, M.  1983.  An Introduction to Solar Radiation.
             Academic Press, NY., page 13 */
     S_tst    = ( 180.0 + S_hrang ) * 4.0;
     S_tstfix = S_tst - S_hour * 60.0 - S_minute - S_second / 60.0;
     S_eqntim = S_tstfix + 60.0 * S_timezone - 4.0 * S_longitude;
 
     /* Sunrise and sunset times */
     if ( S_ssha <= 1.0 ) {
         S_sunrise   =  2999.0;
         S_sunset    = -2999.0;
     }
     else if ( S_ssha >= 179.0 ) {
         S_sunrise   = -2999.0;
         S_sunset    =  2999.0;
     }
     else {
         S_sunrise   = 720.0 - 4.0 * S_ssha - S_tstfix;
         S_sunset    = 720.0 + 4.0 * S_ssha - S_tstfix;
     }
 
     /* Solar azimuth angle */
         /*  Iqbal, M.  1983.  An Introduction to Solar Radiation.
             Academic Press, NY., page 15 */
     ce         = sin ( raddeg * S_zenetr );
     se         = cos ( raddeg * S_zenetr );
 
     S_azim     = 180.0;
     cecl       = ce * cl;
     if ( fabs ( cecl ) >= 0.001 ) {
         ca     = ( se * sl - sd ) / cecl;
         if ( ca > 1.0 )
             ca = 1.0;
         else if ( ca < -1.0 )
             ca = -1.0;
 
         S_azim = 180.0 - acos ( ca ) * degrad;
         if ( S_hrang > 0 )
             S_azim  = 360.0 - S_azim;
     }
 
     /* Refraction correction */
         /*  Zimmerman, John C.  1981.  Sun-pointing programs and their
 accuracy.
             SAND81-0761, Experimental Systems Operation Division 4721,
             Sandia National Laboratories, Albuquerque, NM. */
 
     elev = 90.0 - S_zenetr;
 
     /* If the sun is near zenith, the algorithm bombs; refraction near 0 */
     if ( elev > 85.0 )
         refcor = 0.0;
 
     /* Otherwise, we have refraction */
     else {
         tanelev = tan ( raddeg * elev );
         if ( elev >= 5.0 )
             refcor  = 58.1 / tanelev -
                       0.07 / ( pow (tanelev,3) ) +
                       0.000086 / ( pow (tanelev,5) );
         else if ( elev >= -0.575 )
             refcor  = 1735.0 + elev * ( -518.2 + elev * ( 103.4 +
                                elev * ( -12.79 + elev * 0.711 ) ) );
         else
             refcor  = -20.774 / tanelev;
 
         prestemp    = ( S_press * 283.0 ) / ( 1013.0 * ( 273.0 + S_temp ) );
         refcor     *= prestemp / 3600.0;
     }
 
     /* Refracted solar elevation angle */
     S_elevref = elev + refcor;
 
     /* (limit the degrees below the horizon to 9) */
 //    if ( S_elevref < -9.0 )
 //        S_elevref = -9.0;
 
     /* Refracted solar zenith angle */
     S_zenref  = 90. - S_elevref;
 
     /* Airmass */
         /*  Kasten, F. and Young, A.  1989.  Revised optical air mass
 tables and
             approximation formula.  Applied Optics 28 (22), pp. 4735-4738 */
     cz = cos ( raddeg * S_zenref );
     if ( S_zenref > 93.0 )
         S_amass = -1.0;
     else
         S_amass = 1.0 / ( cz + 0.50572 * pow ((96.07995 - S_zenref),-1.6364) );
 
     S_ampress   = S_amass * S_press / 1013.0;
 
     /* Prime and Unprime */
     /* Prime  converts Kt to normalized Kt', etc.
        Unprime deconverts Kt' to Kt, etc. */
         /*  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), pp. 111-114 */
     S_unprime = 1.031 * exp ( -1.4 / ( 0.9 + 9.4 / S_amass ) ) + 0.1;
     S_prime   = 1.0 / S_unprime;
 
     /* Cosine of the angle between the sun and a tipped flat surface,
        useful for calculating solar energy on tilted surfaces */
     ca        = cos ( raddeg * S_azim );
     cp        = cos ( raddeg * S_aspect );
     ct        = cos ( raddeg * S_tilt );
     sa        = sin ( raddeg * S_azim );
     sp        = sin ( raddeg * S_aspect );
     st        = sin ( raddeg * S_tilt );
     sz        = sin ( raddeg * S_zenref );
     S_cosinc  = cz * ct + sz * st * ( ca * cp + sa * sp );
 
     /* Extraterrestrial (top-of-atmosphere) solar irradiance */
     if ( cz > 0.0 ) {
         S_etrn = S_solcon * S_erv;
         S_etr  = S_etrn * cz;
     }
     else {
         S_etrn = 0.0;
         S_etr  = 0.0;
     }
  
     if ( S_cosinc > 0.0 )
         S_etrtilt = S_etrn * S_cosinc;
     else
         S_etrtilt = 0.0;
 
     return ( 0 );
 }

Here is the caller graph for this function:

Variable Documentation

§ S_amass

double S_amass

O: Relative optical airmass.

Definition at line 41 of file SOLPOS.C.

Referenced by S_solpos().

§ S_ampress

double S_ampress

O: Pressure-corrected airmass.

Definition at line 42 of file SOLPOS.C.

Referenced by S_solpos().

§ S_aspect

double S_aspect

I: Azimuth of panel surface (direction it faces) N=0, E=90, S=180, W=270, DEFAULT = 180

Definition at line 43 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_azim

double S_azim

O: Solar azimuth angle: N=0, E=90, S=180, W=270.

Definition at line 45 of file SOLPOS.C.

Referenced by D_AutoExecution(), E_Almucantar(), E_DirectSun(), E_IRefSun(), MIGEActualZenAz(), MIGEAntiSunTrack(), MIGEAz(), MIGESunTrack(), S_solpos(), SD_PosAADev(), SZA_FirstCalc(), and Task_Timer().

§ S_cosinc

double S_cosinc

O: Cosine of solar incidence angle on panel.

Definition at line 46 of file SOLPOS.C.

Referenced by S_solpos().

§ S_day

int S_day

I/O: Day of month (May 27 = 27, etc.) I/O: Day of month (May 27 = 27, etc.) S_solpos needs this, but S_date will calculate it from S_daynum.

Definition at line 33 of file SOLPOS.C.

Referenced by S_date(), and S_solpos().

§ S_dayang

double S_dayang

T: Day angle (daynum*360/year-length) degrees.

Definition at line 47 of file SOLPOS.C.

Referenced by S_solpos().

§ S_daynum

int S_daynum

I/O: Day number (day of year; Feb 1 = 32 ) I/O: Day number (day of year; Feb 1 = 32 ) S_date needs this, but S_solpos will calculate it from S_month and S_day.

Definition at line 34 of file SOLPOS.C.

Referenced by S_date(), S_solpos(), and SZACalc().

§ S_declin

double S_declin

T: Declination–zenith angle of solar noon at equator, degrees NORTH

Definition at line 48 of file SOLPOS.C.

Referenced by S_solpos().

§ S_eclong

double S_eclong

T: Ecliptic longitude, degrees */.

Definition at line 50 of file SOLPOS.C.

Referenced by S_solpos().

§ S_ecobli

double S_ecobli

T: Obliquity of ecliptic */.

Definition at line 51 of file SOLPOS.C.

Referenced by S_solpos().

§ S_ectime

double S_ectime

T: Time of ecliptic calculations */.

Definition at line 52 of file SOLPOS.C.

Referenced by S_solpos().

§ S_elevref

double S_elevref

O: Solar elevation angle, deg. from horizon, refracted

Definition at line 53 of file SOLPOS.C.

Referenced by S_solpos().

§ S_eqntim

* double S_eqntim

T: Equation of time (TST - LMT), minutes */.

Definition at line 55 of file SOLPOS.C.

Referenced by S_solpos().

§ S_erv

double S_erv

T: Earth radius vector (multiplied to solar constant)

Definition at line 56 of file SOLPOS.C.

Referenced by S_solpos().

§ S_etr

* double S_etr

O: Extraterrestrial (top-of-atmosphere) W/sq m global horizontal solar irradiance

Definition at line 58 of file SOLPOS.C.

Referenced by S_solpos().

§ S_etrn

* double S_etrn

O: Extraterrestrial (top-of-atmosphere) W/sq m direct normal solar irradiance

Definition at line 60 of file SOLPOS.C.

Referenced by S_solpos().

§ S_etrtilt

* double S_etrtilt

O: Extraterrestrial (top-of-atmosphere) W/sq m global irradiance on a tilted surface

Definition at line 62 of file SOLPOS.C.

Referenced by S_solpos().

§ S_gmst

* double S_gmst

T: Greenwich mean sidereal time, hours */.

Definition at line 64 of file SOLPOS.C.

Referenced by S_solpos().

§ S_hour

int S_hour

I: Hour of day, 0 - 23, DEFAULT = 12 I: Hour of day, 0 - 23, DEFAULT = 12.

Definition at line 35 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_hrang

double S_hrang

T: Hour angle–hour of sun from solar noon, degrees WEST

Definition at line 65 of file SOLPOS.C.

Referenced by S_solpos().

§ S_julday

* double S_julday

T: Julian Day of 1 JAN 2000 minus 2,400,000 days (in order to regain single precision)

Definition at line 67 of file SOLPOS.C.

Referenced by S_solpos().

§ S_latitude

* double S_latitude

I: Latitude, degrees north (south negative) */.

Definition at line 69 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_lmst

double S_lmst

T: Local mean sidereal time, degrees */.

Definition at line 71 of file SOLPOS.C.

Referenced by S_solpos().

§ S_longitude

double S_longitude

I: Longitude, degrees east (west negative) */.

Definition at line 70 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_minute

int S_minute

I: Minute of hour, 0 - 59, DEFAULT = 0 I: Minute of hour, 0 - 59, DEFAULT = 0.

Definition at line 36 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_mnanom

double S_mnanom

T: Mean anomaly, degrees */.

Definition at line 72 of file SOLPOS.C.

Referenced by S_solpos().

§ S_mnlong

double S_mnlong

T: Mean longitude, degrees */.

Definition at line 73 of file SOLPOS.C.

Referenced by S_solpos().

§ S_month

int S_month

I/O: Month number (Jan = 1, Feb = 2, etc.) I/O: Month number (Jan = 1, Feb = 2, etc.) S_solpos needs this, but S_date will calculate it from S_daynum.

Definition at line 37 of file SOLPOS.C.

Referenced by S_date(), and S_solpos().

§ S_press

double S_press

I: Surface pressure, millibars, used for refraction correction and S_ampress

Definition at line 75 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_prime

* double S_prime

O: Factor that normalizes Kt, Kn, etc. */.

Definition at line 76 of file SOLPOS.C.

Referenced by S_solpos().

§ S_rascen

double S_rascen

T: Right ascension, degrees */.

Definition at line 74 of file SOLPOS.C.

Referenced by S_solpos().

§ S_sbcf

double S_sbcf

O: Shadow-band correction factor */.

Definition at line 77 of file SOLPOS.C.

Referenced by S_solpos().

§ S_second

int S_second

I: Second of minute, 0 - 59, DEFAULT = 0 I: Second of minute, 0 - 59, DEFAULT = 0.

Definition at line 38 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_solcon

double S_solcon

T: Solar constant, 1367 W/sq m */.

Definition at line 78 of file SOLPOS.C.

Referenced by S_solpos().

§ S_ssha

double S_ssha

T: Sunset(/rise) hour angle, degrees */.

Definition at line 79 of file SOLPOS.C.

Referenced by S_solpos().

§ S_sunrise

double S_sunrise

O: Sunrise time, minutes from midnight, local, no refraction

Definition at line 80 of file SOLPOS.C.

Referenced by S_solpos(), SZA_FirstCalc(), and Task_Timer().

§ S_sunset

* double S_sunset

O: Sunset time, minutes from midnight, local, no refraction

Definition at line 82 of file SOLPOS.C.

Referenced by S_solpos(), SZA_FirstCalc(), and Task_Timer().

§ S_temp

* double S_temp

I: Ambient dry-bulb temperature, degrees C, used for refraction correction

Definition at line 84 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_tilt

* double S_tilt

I: Degrees tilt from horizontal of panel */.

Definition at line 85 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_timezone

double S_timezone

I: Time zone, east (west negative). USA: Mountain = -7, Central = -6, etc.

Definition at line 86 of file SOLPOS.C.

Referenced by S_solpos(), and SZACalc().

§ S_tst

* double S_tst

T: True solar time, minutes from midnight */.

Definition at line 88 of file SOLPOS.C.

Referenced by S_solpos().

§ S_tstfix

double S_tstfix

T: True solar time - local standard time */.

Definition at line 89 of file SOLPOS.C.

Referenced by S_solpos().

§ S_unprime

double S_unprime

O: Factor that denormalizes Kt', Kn', etc. */.

Definition at line 90 of file SOLPOS.C.

Referenced by S_solpos().

§ S_utime

double S_utime

T: Universal (Greenwich) standard time */.

Definition at line 91 of file SOLPOS.C.

Referenced by S_solpos().

§ S_year

int S_year

I: 4-digit year (2-digit is assumed 19xx) I: 4-digit year (2-digit is assumed 19xx) DEFAULT = 2001.

Definition at line 39 of file SOLPOS.C.

Referenced by S_date(), S_solpos(), and SZACalc().

§ S_zenetr

double S_zenetr

T: Solar zenith angle, no atmospheric correction (= ETR)

Definition at line 92 of file SOLPOS.C.

Referenced by AutoRange(), ChkMaster(), D_AutoExecution(), D_BuildH(), D_FixSZA(), D_WaitSZA(), DB_Pause(), E_AAMeasure(), E_Almucantar(), E_DirectSun(), E_IRefSun(), FTP_Back_UP(), HeaderInPlot(), MIGEActualZenAz(), MIGEAntiSunTrack(), MIGESunTrack(), S_solpos(), SZA_FindMin(), SZA_FirstCalc(), Task_CCD_Temp(), Task_LIS_Temp(), and Task_Timer().

§ S_zenref

* double S_zenref

O: Solar zenith angle, deg. from zenith, refracted

Definition at line 94 of file SOLPOS.C.

Referenced by S_solpos().

Functions

Variables

Detailed Description

Function Documentation

§ S_date()

§ S_solpos()

Variable Documentation

§ S_amass

§ S_ampress

§ S_aspect

§ S_azim

§ S_cosinc

§ S_day

§ S_dayang

§ S_daynum

§ S_declin

§ S_eclong

§ S_ecobli

§ S_ectime

§ S_elevref

§ S_eqntim

§ S_erv

§ S_etr

§ S_etrn

§ S_etrtilt

§ S_gmst

§ S_hour

§ S_hrang

§ S_julday

§ S_latitude

§ S_lmst

§ S_longitude

§ S_minute

§ S_mnanom

§ S_mnlong

§ S_month

§ S_press

§ S_prime

§ S_rascen

§ S_sbcf

§ S_second

§ S_solcon

§ S_ssha

§ S_sunrise

§ S_sunset

§ S_temp

§ S_tilt

§ S_timezone

§ S_tst

§ S_tstfix

§ S_unprime

§ S_utime

§ S_year

§ S_zenetr

§ S_zenref