Page 269 - Applied Photovoltaics

Expressions

ª 2ʌ º
DEC 23 . 45 « qsin 284 NDY »
¬ 365 ¼
or more accurately
DEC 332810. 22. 984 cos N 73723. sin N 34990. cos 2N
032050. sin 2N 13980. cos 3N 071870. sin 3N
360 q
N NDY
365
15 HRA 12 q hour
ALT asin > sin LAT cos DEC cos LAT cos HRA @sin DEC
ªcos LAT sin DEC cos DEC sin LAT cos HRA º
AZI ' acos « »
¬ cos ALT ¼
­ AZI , ' for HRA (i.e.0 AM)
AZI ®
¯ 360 q AZI , ' for HRA ! (i.e.0 PM)
HSA AZI ORI
ª tan ALT º
VSA atan « »
¬ cos HRA ¼
INC acos > cosTIL cos ALT sinTIL cos HSA @sin ALT
­acos > cos HSA @cos ALT , for vertic al surfaces
®
¯ ZEN 90 q ALT , for horizontal surfaces
SRA acos > sin DEC tan LAT tan DEC sin LAT cos DEC @cos LAT
acos tan DEC tan LAT
SRT 12
15 q
For an alternative method, the US Naval Observatory (2003) gives “an algorithm for
computing the sun’s angular coordinates to an accuracy of about 1 arcminute within
two centuries of 2000”.

REFE RE NCES
Updated World Wide Web links can be found at www.pv.unsw.edu.au/apv_book_refs.

US Naval Observatory (2003), Approximate Solar Coordinates
(aa.usno.navy.mil/faq/docs/SunApprox.html).

256