solar angle

The wattsun website has some tools you can use for this purpose.  http://www.wattsun.com/

Rene,

I use this Navy site to adjust mine.
http://aa.usno.navy.mil/data/docs/AltAz.php

John

i have a yahoo widget that calculates solar angle and all that cool stuff, if you use yahoo widgets.

It will take a year to get the results but once you have them you can tune in your PV array to your exact location with two simple items; one is an angle finder and the other is a block of 2"x4"x12" cut square at both ends. You can check once a month or check it on the solstices and equinoxes or when ever you want.
At 12:00 noon on the day you want to know the perfect angle, hold the block of 2"x4" too the face of the PV array, adjust the array until there is no shadow any where around the block, then just hold the angle finder to it and there you have it. Of course you may want to write it down somewhere or maybe drill set holes in the adjuster legs or something. This all depends on the PV array facing solar south during the winter solstice. On the shortest day of the year in my region at 12:00 my block doesn't cast a shadow but at 12:00 on the longest day this doesn't happen until 1:30 which fine because there is still lots of daylight left.

Or you could just dispense with all of it like I do and once a month adjust the array so that there is a slight shadow on the top side of the 2"x4" block of wood or bottom if progressing from winter to spring and then summer again. This assures that the sun is coming in perpendicular to the array as the month progresses. Its a chore but one that I like doing because it also gives me a chance to clean and inspect the array and array mount and all. So far so good.

Rene, you live at 42 deg. N, so, 15 deg. either way gives you, 57 and 27 deg. The angle you are concerned with is the angle between the panel and the horizontal ground using the spot where the panel touches the ground as the vertex.
 So if your panel is standing vertical on the ground, lean the panel back until it makes an angle of 42 deg with the ground below it. This will be the spring and fall location. Then it only makes sense after that. In the winter, raise the panel by rotating it up another 15 deg. towards vertical, until it makes an angle of 57 deg. with the ground. In the summer, rotate it more towards the horizontal, until it is 27 deg. with the ground. 
 But as others have noted, if the rack is easily adjustable just adjust monthly or weekly as needed.