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Zeile 1: + + + + + + + + + + + + − + − + − + − + − To calculate the solar azimuth and elevation exactly+ − you need very involved formulas. However, for practical+ Zeile 18:
Zeile 30: − + − (doubles have the same precision as floats on Arduino)+ − + + + + + + + + + + + + + + + + + + + + + + + + + + +
Solar Arduino tracker (Quelltext anzeigen)
Version vom 9. März 2015, 15:04 Uhr
, 15:04, 9. Mär. 2015→SPA Algorithm
German version [[Sonnenstandsberechner (für sun tracker devices)]]
German version [[Sonnenstandsberechner (für sun tracker devices)]]
=General considerations=
For calculating the solar position with a microcontroller (on a fixed geographic place)
you have to solve two problems:
The controller needs a time device (typically a battery buffered chip like in a PC)
and it needs a reasonably simple algorithm to calculate solar azimuth and
elevation from date, time and geographic position (longitude and latitude).
An algorithm which works on a PC might have problems on a microcontroller.
For instance, on Arduino you must take into account that
''double'' data type has the same precision as float (IEEE 23 bit mantissa)
==Get the Time==
[[Image:Arduino_DS1307_FritzingExport.jpg|thumb|timer chip DS1307 with Arduino]]
To get Greenwich Time (aka UT) I use a DS1307 chip.
To get Greenwich Time (aka UT) I use a DS1307 chip.
Following the description of http://www.glacialwanderer.com/hobbyrobotics/?p=12
Following the description of http://www.glacialwanderer.com/hobbyrobotics/?p=12
it worked immediately. Did not find any 2.2K resistors, it worked with
it worked immediately. Did not find any 2.2K resistors,
4.7K as well.
4.7K ones are just as fine.
I have taken the code from this site and tucked the complexity
I have taken the code from that site and tucked the complexity
into an Arduino libary (DS1307.h)
into an Arduino libary (DS1307H.h)
==Calculate Azimuth and Elevation==
==Calculate Azimuth and Elevation==
The formulas for exact calculation of solar azimuth and elevation
are very involved. However, for practical
purposes like sun tracking of a heliostat there are
purposes like sun tracking of a heliostat there are
simpler ones available.
simpler ones available.
and you can download it [http://www.psa.es/sdg/sunpos.htm here] as C++ code.
and you can download it [http://www.psa.es/sdg/sunpos.htm here] as C++ code.
There are adaptions neccessary for Arduino, though.
There are adaptions neccessary for Arduino, though.
The formulas for calculating the [http://en.wikipedia.org/wiki/Julian_day Juliand Day]
The formulas for calculating the [http://en.wikipedia.org/wiki/Julian_day Julian Day]
are not working properly on Arduino due to reduced double precision.
are not working properly on Arduino due to reduced double precision.
Therefore, I have adapted them, expecting only Julians dates starting from 1.Jan. 2000.
Therefore, I have adapted them (expecting Julians dates from 1.Jan. 2000).
These calculations I have put into another library (Helios.h)
These calculations I have put into another library (Helios.h)
Use following program plus libraries for older Arduino IDE (0023 and older):
{{zip|SolarTracker4Arduino.zip|14KB|Version from 09.03.2011}}
For newer Arduino IDE (1.0.1 and later) use instead the following package,
{{zip|SolarTracker4Arduino1.0.1.zip|17KB|Version from 16.01.2015}}
Once you got it running, verify the calculated positions, for instance with
[http://www.sunearthtools.com/dp/tools/pos_sun.php solar position calculator] from
sunearthtools. (Attention: SolarTracker4Arduino does NOT account for daylight saving time (DST),
you have to determine UT (when you set your timer chip) as if there was no DST at all. On the other hand, sunearthtools allow using DST,
and this option is selected by default.
==SPA Algorithm==
A much more accurate solar algorithm seems to be from Reda, I.; Andreas, A. (2003):
''Solar Position Algorithm for Solar Radiation Applications. NREL Report No. TP-560-34302,
''Revised January 2008. The algorithm is supposed to work for the years -2000 to 6000,
''with uncertainties of +/-0.0003 degrees.''
In this paper methods have been worked out according to the book from
''Jean Meeus: Astronomical Algorithms, Willmann-Bell, Richmond 2000 (2nd ed., 2nd printing)''
a well known text book for astronomic calculations.
The calculations are, however, very extensive; for Arduino I chose the simpler PSA.
Implementations and references for both algorithms I found thanks to the code from
[http://klaus.e175.net/solarpositioning Klaus Brunner]. It was also a valuable help for debugging
the Arduino implementation.
--[[User:Hannes.hassler|Hannes.hassler]] 13:36, 3 March 2011 (CET)