On trial: the components at the very heart of PV systems

102 of these are installed at the Brandenburg-Briest solar park, and almost 1900 at the plant in Jännersdorf in Brandenburg. The video on the construction of the Weesow-Willmersdorf solar park in the Barnim district, which was connected to the grid in November 2020, demonstrates exactly how the valuable pieces of equipment are transported on trucks and carefully lifted down by a crane. We’re talking about inverters, without which no photovoltaic system could feed its power into the grid. Because to do this, the direct current generated by solar modules from sunlight must first be converted into alternating current: the task of the inverters. “Inverters are at the heart of every PV system,” says Prof. Dr Horst Schulte. How reliably the solar power flows depends on their quality and performance, an area in which the engineering scientist sees a pressing need for further research.

Insufficient knowledge regarding equipment wear and lifespan

Is more research still necessary at a time when two million photovoltaic systems are already in service in Germany alone, and an impressive 52.65 terawatt hours of electrical energy were fed into the grid with the help of countless inverters last year (2022)? Prof. Dr. Schulte states that their technical level is indeed high. A large number of manufacturers and performance classes also exists. The only drawback is that too little is still known about potential sources of equipment malfunction, in addition to the fact that ageing processes, wear and tear and the service life of the inverters have not yet been sufficiently investigated, not to mention digital monitoring to detect technical problems at an early stage and avoid them if possible through predictive maintenance. “What’s at stake is the resilience of the PV systems,” says the expert in control engineering and system dynamics. Said resilience is growing in significance thanks to the increasing importance of photovoltaics for the global energy supply. Their share in the German energy mix is currently 10.7 per cent. By comparison, wind energy already contributes 25.1 percent (as of 2022).

The wind energy sector is further ahead

In the case of wind turbines, whose output and energy yield have grown considerably, the challenges in terms of damage analysis have already been overcome to a large extent. “Condition monitoring systems are increasingly being used, which employ sensors to record vibrations, temperature and humidity, for example, reporting abnormalities at an early stage that can be dealt with by taking swift action,” says Prof. Dr. Schulte, who conducted a research project on this topic funded by the Federal Ministry of Education and Research (BMBF) between 2011 and 2014. Like all engineers in his field, he differentiates between the “fault”, in which a technical system is disrupted but is not paralysed if the damage is recognised, analysed and repaired in time, and the “failure”, the failure of the system, which must be prevented.

Focus on quality, performance and uptime

Prof. Dr. Schulte seeks to transfer the knowledge gained in the use of wind energy to the PV sector. He would like to start by focusing on the inverters, where he sees the greatest potential for optimisation. The goal: a systematic evaluation of the equipment’s quality, performance and uptime. The engineering scientist has in mind an index featuring different categories that allows an holistic view of the inverters. On the one hand, such an index could assist operators of and investors in solar parks, who currently focus most of their attention on costs and (must inevitably) compare inverters based on individual values.

Manufacturer-independent criteria

On the other hand, a comprehensive reliability analysis could provide manufacturers with fresh impetus for the equipment’s further development. “We aim to explore dependencies that we have only guessed at so far and establish these during operations in varying environments,” says Prof. Dr. Schulte. He muses that perhaps one of the electronic components should be made at a larger scale or out of better materials, enabling them to withstand the load for longer. He believes that this option requires investigation, and that regular operating data from PV power plants should be included in order to be able to define criteria that are as general and manufacturer-nonspecific as possible.

The energy transition could make faster progress

In combination with the expansion of the software already installed in inverters today, comprehensive monitoring including early fault detection, known in technical jargon as “predictive maintenance”, could be developed based on machine learning methods when scientifically substantiated knowledge is available for PV inverters, as is the case for wind turbines. Such findings pertain, for instance, to which components fail and when, under which circumstances, why and how quickly, potentially leading to the failure of the solar system. “Operators could time maintenance work more effectively, minimise feed-in interruptions, avoid subsequent faults and reduce repair costs,” says Prof. Dr. Schulte, listing the positive effects. They would help to speed up the overdue energy transition.