We've improved our performance reporting, especially for east and west facing systems. What does this mean?
One of our primary goals is to be able to enable you to measure the performance of your PV system, so you can see if something has gone wrong. In order to do this we report the performance ratio (PR) of registered systems on a monthly basis. This allows you to compare your system with others regardless of size, location or orientation.
The PR of a system describes how its performance compares with a perfect system. No real system is perfect, so the PR is usually around 70 - 90%. The PR often decreases in winter for those systems which suffer seasonal shading, but rises slightly for those that don't.
If something goes wrong with your system it is likely to reduce its performance, so by viewing your graph of PR over time you may be able to identify this drop.
We have now improved our method for calculating the performance of systems, especially those which face east or west. This should make it easier for you to spot a drop in your PR, should something go wrong.
If your system faces south, it is unlikely that you will see much difference to the PR values, but if it faces east or west you are likely to see a significant drop in the new report (see the figure below).
Check the performance maps to see how your system has been affected.
The image is an example of an east/west facing system, showing the difference between previous and current reporting. Note that previous readings were almost all above 100%. Though this can occur on occasion due to variability of weather and suchlike, it should be a rare occurrence.