That's OK - go ahead and take measurements when you can, no matter whether the sun is out or not - but that is an important item to record.OK everything sounds really easy except for one item. A sunny day.
I hear we are supposed to get one Sunday.
Preferably, around 10am, around 1pm-3pm, and maybe 5pm or so.
After all, you want this thing to work even if it's not really sunny out, right?