What is the biggest problem with PV plants? They may work, but you can never be sure how well or whether they ever achieve the maximum performance of which they are capable. Or whether slow-burning problems such as PID are developing. And indeed, the International Energy Agency (IEA) found in a major study that most plants do not deliver the performance they could - but hardly a single operator is aware of this.

And how could they be? So far, monitoring occurs mainly only at the current collection points such as the inverters, and sometimes at the strings.

Discrepancies in measurements show THAT there is a problem, but not ITS NATURE. Or even WHICH MODULE is concerned.

But when I know, THAT there is a problem, how can I find out at little expense, WHAT to do?

© Graphic: International Energy Agency

Until now, monitoring meant the collection of data. In order to interpret this data, specialists and expensive and time-consuming on-site investigations were necessary.
Over the course of its lifetime, a module may face diverse errors - which can worsen over the years. Besides degradation this can be delamination, or cell corrosion, cell cracks, micro cracks, Hot Spots, PID, etc....


1. Infant-failure phase, in which a degradation of 0.5-5% is usual, which then consolidates on that level ("Light-Induced-Degradation", LID).
2. Midlife-failure phase, in which problems increase, like cell cracks due to hail impact, delamination, EVA-discoloring, etc.
3. Wear-out-failure phase, when warranties are expired but problems get cummulated and enlarged due to usual wear-out and dragged but never repaired issues.

There are many causes for problems and losses for modules. Consequences may be solely temporary power or voltage reduction, or can be more grave, like Hot Spots for example - these can destroy the module or lead to fire of the plant. Bypass-diodes offer protection, but they are neither meant nor made for non-stop-useage. They can become defective as well. And a single defective bypass-diode lowers the performance of a module by 33%!

With string monitoring at best, you have to check the string manually, as soon as a power reduction has been found.

If the plant is monitored only by the inverter, the whole plant is a kind of "black box": so in case of a power reduction the whole plant has to be checked manually.

Usually, the investment of a PV plant can be assessed only after a year of operation. Performance ratio assessments on a more short notice are not reliable, as the very temperature fluctuations distort the result strongly. Module temperature has a striking impact on the module performance. Wind can lower the temperature of a module rapidly by 20°C - resulting in performance differences of 8.8%!