Changes

Jump to navigation Jump to search
1,715 bytes added ,  15:04, 9 March 2015
Line 2: Line 2:     
=General considerations=
 
=General considerations=
To calculate the solar position with a microcontroller (on a fixed geographic place)  
+
For calculating the solar position with a microcontroller (on a fixed geographic place)  
 
you have to solve two problems:  
 
you have to solve two problems:  
 
The controller needs a time device (typically a battery buffered chip like in a PC)
 
The controller needs a time device (typically a battery buffered chip like in a PC)
Line 12: Line 12:     
==Get the Time==
 
==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 immediately. Did not find any 2.2K resistors,  
 
4.7K ones are just as fine.   
 
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==
To calculate the solar azimuth and elevation exactly
+
The formulas for exact calculation of solar azimuth and elevation  
you need very involved formulas. However, for practical
+
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.  
Line 29: Line 30:  
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 from 1.Jan. 2000).
+
Therefore, I have adapted them, expecting only Julians dates starting 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)
33

edits

Navigation menu