Housing shots and solar panel scan

We were enlisted to do Aerial roof shots with an added solar scan, The roof shots were run of the mill but the results we achieved from the solar scan revealed that one panel had imminent failures happening. we have completed a report on the finding and it has been sent through to the suppliers for further analysis. The clients' solar panel was replaced and she in now getting the full possible solar available. She has since called us to say now that her panel has been repaired her Power bill reduced by $300 in the 60-day cycle. What it tells us is when one panel goes down it can have a chain reaction effect on surrounding panels. Her panels were two years old so has she been paying for the extra power as her panels were not running inefficiently?