About 18 months ago we had solar panels installed on Geoger Towers (this may or may not be an accurate description of the Geoger office!). With this comes the ability to monitor power generation and use, as well as a host of other things. During the install we were warned that a small tree in a neighbouring patch of land might create an issue with generation in future years by shadowing out the light falling on the panels.
What is interesting is that it is a totally different tree that is causing a drop in our power generating potential. A (very) large ash that is about 4 properties away is actually the culprit – but only when we have very low sun-angles (such as in mid-winter). The two figures below show the drop off in power generation (orange line) due to shadowing (and also that I microwaved a baked potato on Tuesday evening – blue line). This drop-off effect wasn’t noticed last year, in part because the tree wasn’t so big (there is a dispute over who has responsibility for it, so it hasn’t been managed at all), in part because last winter was so cloudy so the values were less defined and in part because I don’t check the charts that often.
So the upshot of this is, whatever you are measuring, know your site and know all the things around it that might impact on your measurements!