100% SunSniffer® = 100% Transparency

Why module precise is important


Selection of possible Errors and defects:

Potential or light induces degration reduce the Performance continually, without being noticed. And without constant voltage measurement in the module, PID recognition in the field is simply impossible.

Common detection: Electroluminescence / open-circuit voltage measurements
Necessary requirements: Plant inspecton / good access to the modules

Detection by SunSniffer: Measurement and analysis of module voltage

One defective diode reduces modules voltage to 66%, two defective diodes down to 33%. This is not noticeable without measurement of modules voltages.

Common detection: Junction box opening / open-circuit voltage measurements
Necessary requirements: Plant inspecton / good access to the modules

Detection by SunSniffer: Measurement and analysis of module voltage


Badly-soldered connections or structural defects in the cell cause selective heat productions at those spots. Any hot spot is a power leakage. 

Common detection: IR-thermography / visual inspection
Necessary requirements: Plant inspecton / good access to the modules

Detection by SunSniffer: Measurement and analysis of module voltage


Hail can cause serious defects of cells. Cracks in a cell may be small, but can cause or accelerate degradation.

Common detection: Electroluminescence / visual inspection
Necessary requirements: Plant inspecton / good access to the modules

Detection by SunSniffer: Measurement and analysis of module voltage


Further information:

Solar Bankability

Internationale Energie Agentur

Fraunhofer CSP

TÜV Rheinland

ZAE Bayern





The market for sustainable, renewable energies is growing fast and, in recent years, great progress in terms of the overall efficiency of PV systems has been made. In order to follow the constantly growing PV market it is necessary to develop more sophisticated monitoring tools which are capable of finding a fault or failure in the PV system as soon as possible. The ability to predict failures by monitoring changes in system parameters offers plant owners the possibility to increase profitability by decreasing downtime.

A recent study by the International Energy Agency found that PV plants are performing at a satisfactory level within given parameters but could achieve higher levels of output. “Task 13”, a research project set up by the Photovoltaic Power System Programme (PVPS), a cooperation platform within the IEA, set out to investigate module errors, analytical monitoring methods and long-term performance analyses. Its findings can be summarised thus (all IEA PVPS Task 13 reports can be found here):

• Faults and defects reduce PV plant efficiency
• Fault finding and troubleshooting must be carried out in greater depth
• IEA recommendation: measurements should be taken directly at the junction box

The Performance Ratio (PR) of PV plants has increased by up to 20% today when compared to 35 years ago, with some plants running at as much as 90%. Others, however, can only point to a value of 70%. Investor confidence would be greatly boosted by increasing the PR to a higher, sustained level, resulting in higher bankability, lower capital costs and hence lower production costs. The way to achieving this is through rapid, exact fault finding. As things stand at the moment, profit-reducing faults remain, in some cases, undetected. If detected, a more exact analysis of the problem can be prohibitively complicated and expensive. It is true to say that it is less than clear as to which methods are best at finding which faults. Defective bypass-diodes are a case in point. Although they pose a danger to safety, no great effort has been made to find a reliable way with which to detect them (for further information please see IEA PVPS Task 13, Review of Failures of Photovoltaic Modules Final, 2014).

The answer to these problems is module-specific monitoring. The IEA recommends that measurements be taken directly at the junction box. It is impossible to say whether a reduction in performance is due to a system error or merely lower irradiation, when monitoring is conducted only at the power collection point. In the event of a PV plant producing less energy than expected, junction box or string based monitoring significantly reduces the amount of time and money for detecting the failure.

Monitoring at the junction box level is, therefore, strongly recommended. Junction-based monitoring could lead to an increase in revenue of up to 12%. This is in reality a potential 400% increase when compared with the hitherto predicted 3% plant revenue. So the IEA’s recommendation for junction-based monitoring would not only revolutionize O&M of the PV industry but also hugely increase profits for operators. Real-time remote diagnosis enables the taking of immediate action without wasting any time, thus avoiding revenue losses. It pays to remember that defective parts affect not only the performance of part of the plant but the plant as a whole. Precise directives based on intelligent analysis software plus an easily understandable presentation of results facilitate not only a sound decision-making process even before a team of specialists steps foot on the plant, but can also reduce costs even further as the team need not be of an exceptionally high professional grade. Upon the failure being identified the module in question can simply be exchanged resulting in low revenue loss and no extra costs due to the commissioning of a team of specialists to find the failure.

The one remaining question is whether there is already a product on the market that can achieve all this. And the resounding answer is a clear yes. The SunSniffer is capable of all this, collecting and analyzing data at junction box level, making fault finding and elimination child’s play.



Why voltage measurements?

All modules have the same consistant voltage curve over the day. Deviations of this specific value are clear indications of failures. Identifying the same characteristics enables precise error detection - and identification. In this curve you can see the voltage of two modules (orange and black lines) during one day in comparison, which are clearly similar. You can see as well how the temperature (blue line) on that day influenced the voltage: the warmer the modules, the lower the voltage. 

Why temperature measurements?

Module temperatures vary within a plant by 15° Celsius due to different cooling. Temperature has a significant effect on the performance of a module: 15° Celsius reflects a power difference by 6%. How do you know if your system works fine if it can vary within specification by that number? Well - by measuring the temperature of each module and taking this into account of our plant performance calculations! Including module temperature measurements enables us to determine a precise PR - even for shortest periods



Can SunSniffer deliver the same result as infrared thermography?

The common and well-proven way to inspect a PV plant for failures is infrared thermography. This method detects temperature differences. Heatings can point to errors, so this method can locate potential errors easily. Using drones for aerial inspection even accelerates and facilitates examination of a plant. IR images must be interpreted by experts, as heatings can also be caused by reflexions or bad ventilation. And the prerequisites, like weather conditions, need to be suitable for taking IR images. But: defects not only reveal themselves in changed temperature, but even more so in changed power – and even more precisely. Measuring the individual modules power can determine exactly, which module has how much power loss and needs to be swapped. This process being automated, no expert interpretation is needed. In a typical IR image all temperature differences are marked. But information about power losses is not available on IR. Assuming that you are not an expert: Does it help you decide about warranty cases, for example? If you cannot see the degree of power losses? How much are such images supporting you to manage plant issues, without expert comments?

We measure the power of each module every 30 seconds, so power losses are recognized instantly. SunSniffer® does not need to rely on assessments, SunSniffer® measures! Our artificial intelligence analyses the data and clearly recognizes errors. Additionally, we offer precise instructions of what needs to be done - swap the module, or change diodes,... But as we offer an integrated system, we even provide clear guidance through the respective repair processes, with clear instructions, and an App for on-site service including documentation functions.

IR is a helpful tool if you do not have SunSniffer®. But if you have an option the answer is clear: SunSniffer® not only cost you less than all IR tests over the lifespan of your plant, it gives you automatic and instant results - all the time. So SunSniffer® delivers even better results than IR!

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%!