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Note about code source.
1 jpye 2583 /*
2     THIS CODE COMES FROM APPENDIX A.6 OF REPORT NREL/TP-560-34302
3     WHICH WAS OBTAINED FROM
4     http://www.osti.gov/bridge/servlets/purl/15003974-iP3z6k/native/15003974.PDF
5     */
6 jpye 2582
7     /////////////////////////////////////////////
8     // HEADER FILE for SPA.C //
9     // //
10     // Solar Position Algorithm (SPA) //
11     // for //
12     // Solar Radiation Application //
13     // //
14     // May 12, 2003 //
15     // //
16     // Filename: SPA.H //
17     // //
18     // Afshin Michael Andreas //
19     // afshin_andreas@nrel.gov (303)384-6383 //
20     // //
21     // Measurement & Instrumentation Team //
22     // Solar Radiation Research Laboratory //
23     // National Renewable Energy Laboratory //
24     // 1617 Cole Blvd, Golden, CO 80401 //
25     /////////////////////////////////////////////
26    
27     ////////////////////////////////////////////////////////////////////////
28     // //
29     // Usage: //
30     // //
31     // 1) In calling program, include this header file, //
32     // by adding this line to the top of file: //
33     // #include "spa.h" //
34     // //
35     // 2) In calling program, declare the SPA structure: //
36     // spa_data spa; //
37     // //
38     // 3) Enter the required input values into SPA structure //
39     // (input values listed in comments below) //
40     // //
41     // 4) Call the SPA calculate function and pass the SPA structure //
42     // (prototype is declared at the end of this header file): //
43     // spa_calculate(&spa); //
44     // //
45     // Selected output values (listed in comments below) will be //
46     // computed and returned in the passed SPA structure. Output //
47     // will based on function code selected from enumeration below. //
48     // //
49     // Note: A non-zero return code from spa_calculate() indicates that //
50     // one of the input values did not pass simple bounds tests. //
51     // The valid input ranges and return error codes are also //
52     // listed below. //
53     // //
54     ////////////////////////////////////////////////////////////////////////
55    
56     #ifndef __solar_position_algorithm_header
57     #define __solar_position_algorithm_header
58    
59    
60     //enumeration for function codes to select desired final outputs from SPA
61     enum {
62     SPA_ZA, //calculate zenith and azimuth
63     SPA_ZA_INC, //calculate zenith, azimuth, and incidence
64     SPA_ZA_RTS, //calculate zenith, azimuth, and sun rise/transit/set values
65     SPA_ALL, //calculate all SPA output values
66     };
67    
68     typedef struct
69     {
70     //----------------------INPUT VALUES------------------------
71    
72     int year; // 4-digit year, valid range: -2000 to 6000, error code: 1
73     int month; // 2-digit month, valid range: 1 to 12, error code: 2
74     int day; // 2-digit day, valid range: 1 to 31, error code: 3
75     int hour; // Observer local hour, valid range: 0 to 24, error code: 4
76     int minute; // Observer local minute, valid range: 0 to 59, error code: 5
77     int second; // Observer local second, valid range: 0 to 59, error code: 6
78    
79     double delta_t; // Difference between earth rotation time and terrestrial time
80     // It is derived from observation only and is reported in this
81     // bulletin: http://maia.usno.navy.mil/ser7/ser7.dat,
82     // where delta_t = 32.184 + (TAI-UTC) + DUT1
83     // valid range: -8000 to 8000 seconds, error code: 7
84    
85     double timezone; // Observer time zone (negative west of Greenwich)
86     // valid range: -18 to 18 hours, error code: 8
87    
88     double longitude; // Observer longitude (negative west of Greenwich)
89     // valid range: -180 to 180 degrees, error code: 9
90    
91     double latitude; // Observer latitude (negative south of equator)
92     // valid range: -90 to 90 degrees, error code: 10
93    
94     double elevation; // Observer elevation [meters]
95     // valid range: -6500000 or higher meters, error code: 11
96    
97     double pressure; // Annual average local pressure [millibars]
98     // valid range: 0 to 5000 millibars, error code: 12
99    
100     double temperature; // Annual average local temperature [degrees Celsius]
101     // valid range: -273 to 6000 degrees Celsius, error code; 13
102    
103     double slope; // Surface slope (measured from the horizontal plane)
104     // valid range: -360 to 360 degrees, error code: 14
105    
106     double azm_rotation; // Surface azimuth rotation (measured from south to projection of
107     // surface normal on horizontal plane, negative west)
108     // valid range: -360 to 360 degrees, error code: 15
109    
110     double atmos_refract;// Atmospheric refraction at sunrise and sunset (0.5667 deg is typical)
111     // valid range: -5 to 5 degrees, error code: 16
112    
113     int function; // Switch to choose functions for desired output (from enumeration)
114    
115     //-----------------Intermediate OUTPUT VALUES--------------------
116    
117     double jd; //Julian day
118     double jc; //Julian century
119    
120     double jde; //Julian ephemeris day
121     double jce; //Julian ephemeris century
122     double jme; //Julian ephemeris millennium
123    
124     double l; //earth heliocentric longitude [degrees]
125     double b; //earth heliocentric latitude [degrees]
126     double r; //earth radius vector [Astronomical Units, AU]
127    
128     double theta; //geocentric longitude [degrees]
129     double beta; //geocentric latitude [degrees]
130    
131     double x0; //mean elongation (moon-sun) [degrees]
132     double x1; //mean anomaly (sun) [degrees]
133     double x2; //mean anomaly (moon) [degrees]
134     double x3; //argument latitude (moon) [degrees]
135     double x4; //ascending longitude (moon) [degrees]
136    
137     double del_psi; //nutation longitude [degrees]
138     double del_epsilon; //nutation obliquity [degrees]
139     double epsilon0; //ecliptic mean obliquity [arc seconds]
140     double epsilon; //ecliptic true obliquity [degrees]
141    
142     double del_tau; //aberration correction [degrees]
143     double lamda; //apparent sun longitude [degrees]
144     double nu0; //Greenwich mean sidereal time [degrees]
145     double nu; //Greenwich sidereal time [degrees]
146    
147     double alpha; //geocentric sun right ascension [degrees]
148     double delta; //geocentric sun declination [degrees]
149    
150     double h; //observer hour angle [degrees]
151     double xi; //sun equatorial horizontal parallax [degrees]
152     double del_alpha; //sun right ascension parallax [degrees]
153     double delta_prime; //topocentric sun declination [degrees]
154     double alpha_prime; //topocentric sun right ascension [degrees]
155     double h_prime; //topocentric local hour angle [degrees]
156    
157     double e0; //topocentric elevation angle (uncorrected) [degrees]
158     double del_e; //atmospheric refraction correction [degrees]
159     double e; //topocentric elevation angle (corrected) [degrees]
160    
161     double eot; //equation of time [minutes]
162     double srha; //sunrise hour angle [degrees]
163     double ssha; //sunset hour angle [degrees]
164     double sta; //sun transit altitude [degrees]
165    
166     //---------------------Final OUTPUT VALUES------------------------
167    
168     double zenith; //topocentric zenith angle [degrees]
169     double azimuth180; //topocentric azimuth angle (westward from south) [-180 to 180 degrees]
170     double azimuth; //topocentric azimuth angle (eastward from north) [ 0 to 360 degrees]
171     double incidence; //surface incidence angle [degrees]
172    
173     double suntransit; //local sun transit time (or solar noon) [fractional hour]
174     double sunrise; //local sunrise time (+/- 30 seconds) [fractional hour]
175     double sunset; //local sunset time (+/- 30 seconds) [fractional hour]
176    
177     } spa_data;
178    
179     //Calculate SPA output values (in structure) based on input values passed in structure
180     int spa_calculate(spa_data *spa);
181    
182     #endif

john.pye@anu.edu.au
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