Re-inventing O&M: monitoring alone is not enough


Ingmar Kruse is a familiar figure in the German PV industry. As a power plant owner Kruse developed a method to take solar farm monitoring down to the individual module. What has been labeled Independent Module Monitoring (IMM) allowing errors such as hot spots, PID, broken bypass diodes and faulty connectors to be quickly identified and O&M crews directed to precisely where the fault has occurred, so components can be replaced soon after a fault occurs and with an efficient use of O&M resources.

Kruse is now the CTO of Solar Solutions, and IMM being rolled out with AEG’s modules. Solar Solutions is the company behind the reintroduction of AEG modules into the market.

The key component to the IMM system is a sensor. The sensor measures the voltage, current and junction box temperature of each module and relays this data over the DC cabling, via power-line communication, eliminating the need for additional cabling. The discussion about this technology is well known. In principle, operators receive massive amounts of data via module-triggered monitoring, but critics – particularly in Germany – often claim that the benefits do not justify the costs. It’s big data, but is it worth it?

"Monitoring 2.0, through IMM, means that we perform data analysis on the information allowing the system to provide clear instructions to the park owners and operators, even to the technically uninitiated," says Kruse

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A PV plant in the German city of Cadolzburg delivers huge amounts of data, for instance. The modules in the 100 kW installation are equipped with sensors that transmit voltage and temperature data from junction boxes via power lines to the IMM gateway. Power is measured at the end of the strings, and this measurement also goes to the gateway. The gateway transmits the data to the web portal.

Until recently, users could only see the output of each module, much like other electronic systems located near the modules, such as optimizers. IMM is a very stripped-down system compared with an optimizer and costs far less. Whether IMM is cost-effective for park operators can be debated, whether it provides limited benefits, regarding park performance, is no longer in question.

The software localizes the faults of individual module and depicts them in different colors, e.g. for shading, defect bypass diode, disfuncrtioning module.

The data from the 100 kW Cadolzburg array has been comprehensively evaluated, so that the web portal not only sounds an alarm when the module's output diverges significantly from its rated capacity, but also detects module defects automatically.

A €240,000 (US$272,000) research project funded by the German energy ministry (BMWi) and carried out in cooperation with Next Energy EWE research institute and the Bielefeld University of Applied Sciences wrapped up at the end of February. The project assessed the IMM system (under the name of Sunsniffer – from the early stages of product development) by collecting, reviewing and analyzing data from the park. The progression of voltage, current and temperature values over periods of weeks and months clearly indicate whether a module is affected by shading at certain times, is losing performance through potential-induced degradation (PID), whether bypass diodes are defective, or cable connectors are subject to increased resistance or simply dirty.

The research project calculated that the actual energy yields deviated from those measured by the IMM system by just 0.4%. The high degree of accuracy was achieved by measuring the temperature in the junction box. In general, the high level of accuracy of yield calculations means that problems are detected much more quickly.

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Processing the big data

Big data can be a big waste of time if the data is not handled and processed correctly. The IMM system includes software that detects faults automatically and illustrates, over a graphic interface, the affected modules in the module field in a range of colors for the different issues detected (such as PID, defective diodes, shading, broken modules). Service technicians can immediately home in on problems, saving themselves what might otherwise have been a complicated search process.

The program displays the results of the analysis on an online map that can be accessed via a mobile app if the user is at the PV plant. The service technician can identify faults, pack the right equipment for the repair job and go directly to the affected module.

The benefit is obvious. Without this data analysis, service staff looking for the cause of a drop in yield indicated in their monitoring portal first have to root out the problem. They may not find it at all. This is one of the hot issues related to PID if and when the effect shows up in string-based monitoring – a problem that has been well documented in the mature German PV market. IMM may even allow for an error to be detected more quickly than alternative systems.

Amortization rate

Although it may be fun to crunch numbers, the benefit of IMM can be a little tricky to quantify. Ingmar Kruse tackles this with a theoretical 2 MW solar park. Kruse assumes that monitoring improves the performance ratio by three percent because errors can be found sooner and dealt with more efficiently. In many real-life cases, the yield increase achieved through IMM deployment was significantly above 3%.

Kruse suggests an example of a 2 MW park generating 1,200kWh/kWp, with a FIT of €0.09/kWh ($0.10/kWh), and with his “conservative” forecast of 3% yield increase delivered by IMM, plus savings on traditional O&M of €10.50/Wp ($11.90/Wp) of 20%. The return of the IMM yield gain will then stand at €6,480 p.a. ($7,360 p.a.) and O&M cost decrease is €4,200 p.a. ($4,770 p.a.).

The cost-side is easier to calculate. According to Kruse, if IMM was installed at the 2 MW site, it adds up to an investment of €26,300 ($29,860) for a two-megawatt system or €0.013/Wp ($0.015/Wp). On top of that are the annual fees for the monitoring and analysis web portal, which come to approximately €2,800 ($3,180). The investment and annual costs for conventional string monitoring can be subtracted from this figure and the result compared to the expected additional income.

Using this 2 MW example, the IMM system delivers a yield increase and O&M savings totaling of €10,680 p.a. ($12,125 p.a.) on an initial investment of €26,300 ($29,860). This is a return of over 40% on the IMM investment and the cash return on the plant of 22% – without additional costs having been deducted on revenues.

The free webinar, hosted jointly by pv magazine and Solar Solutions, in which the IMM system will be explained in more detail, will include a more detailed cost-benefit analysis. Register here.

But to assess how well the system works, it is important to know more about false alarms. That is, how often are service engineers dispatched to the PV plant for nothing, and how often do they stay put when they ought to be fixing a problem at the plant? It is also important to take into account that system performance only increases if the recommended maintenance activities are carried out, which is not free. "These costs are incurred anyway," says Kruse. But, he adds, the search for the problem is usually the most expensive part of the service cost. He calls this a "revolution in the O&M business.”

One complaint is that module manufacturers have absolutely no interest in the system for fear it would open them up to more warranty claims. "In this case, ignorance is the fear factor," says Kruse. Defective modules have to be replaced sooner or later anyway. “The data analysis will actually relieve manufacturers of liability because very often the module is not the source of the trouble and the data bears that out."

A number of module manufacturers have integrated IMM technology and as of 2017, every AEG module will come with IMM technology by default.

The “Re-inventing O&M” webinar is a collaboration between pv magazine and Solar Solutions.

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