If you have one of those monitor devices supplied by the installer here is one thing it can help you spot. If your results from onyourroof.com show a drop in power generation compared to the average in your area then it may be shading that’s causing this. What differentiates shading from other issues is that it usually occurs at a particular time of day and may even be restricted to a certain time of year.
The best time to test for shading is to look at the dily graph on your monitor at the end of wall to wall sunny day. The power generation curve should have a classic bell-like appearance. Here’s an example of the perfect curve for a roof with a very close to south orientation. For example:
However most of us will usually get some shading at some point of the day. Here’s an example of possible shading in the morning until about 10am. If this pattern occurs every sunny day you will then know that there is some external shading of your panels.
Shading will generally cause ‘bite shaped’ reductions the daily power curve, or the linear type impact as above. Power reduction caused by cloud appearance will have a more ragged and random impact on the curve.
Different times of the year may also cause shading. Below is a shape that you may only get when sun is lower in the sky and some southward trees may only at this time cause shading. The pattern caused here needs only a small amount of shading to cause a significant amount of power reduction. This is a problem that may make the difference between using imported electricity or not in the middle of the day so may be more important to resolve if possible with some pruning of the trees in question.
*This example is illustrative only of a ‘bite shaped’ reduction as this installation is not affected by ground shading