Photovoltaic system owners FAQ

Is my system working properly?

Am I satisfied with the yield of my PV system?

You received a production estimate during the planning phase. Your annual energy statement shows that the forecast production has not been obtained. The production estimate is based on average sunshine hours. The weather does not give a satisfying explanation for the lower yields.

How can I avoid a lower energy yield?

You may want to detect (find) a partial loss of yield or prevent a complete failure of your PV system. A PV system is rather complex. Electrical, mechanical and fire-prevention issues need consideration.
Small defects, initially invisible to the human eye, eventually spread throughout the entire system and can thus lead to a failure of individual parts of your system, or even to a total breakdown due to overheating.

What can be done?

Even if you PV system has been installed conforming to standards: A regular error diagnosis is necessary, usually carried out annually by a certified specialist.

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Sources of error

Breakage of glass

Moisture penetrates through cracks in the glass covers. This will lead to a failure of the inverter.

Insulation damages

The insulation of modules, cables, plugs, and other installations is damaged. This may result in an undesired current flow due to insulation fault, short-circuit or earth fault.

Moisture damages

Condensation may occur in outlets and installations. The result are leakage currents and the corrosion of component parts.

Micro-cracks and hotspots

Micro-cracks are invisible cracks in PV cells. The affected modules consume power and can interconnect the relevant bypass diode. 
Hotspots can occur in these cells and damage the encapsulation material.

Thermal overload

Problems with contacts on conductors will eventually lead to a failure of individual strings or the entire PV system.

Mechanical installation

The mechanical installation of solar panels, parallel to the surface of the roof or elevated, may be the reason for a leaking roof. The type and workmanship of the installation are decisive factors for the durability of a PV system.

Damage by hail

Hailstones may, dependent on their size, cause micro-cracks in PV cells. Again, such damages are not visible to the naked eye.


PID – Potential Induced Degradation is a degradation in crystalline silicon cells connected to transformer-less inverters. This phenomenon leads to performance degenerations, and can be detected in the last modules of a string on the negative pole.

The pictured sources of failure are only a selection.


Thermal overload

Thermal imaging diagnosis of a failure setting in on the outlet of a PV module.

A too high thermal dissipation inside the fuse boxes results in a melting of plastic covers and a partial failure of the fuses.

Mechanical installation

Picture on the left: The roof hook lies on the tile. This PV system is not mounted in accordance with standards.

Picture on the right: There is sufficient room between the tile and the roof hook. A properly installed roof hook ensures a leakage-free roof and prevents a breakage of roof tiles.

Damage to installations

Condensation with resulting corrosion


The colour of a cell changes at 125 °C.


Micro-cracks are invisible to the naked eye. They inevitably result in the failure of the entire module. A thermogram will immediately identify all affected modules.
 left: Front right: Back

Breakage of glass (module)

A breakage of glass in a module is hardly visible to the naked eye. A thermal image (thermogram) is required for successful troubleshooting.

  • Thermal overload

    Thermal overload

  • Mechanical installation

    Mechanical installation

  • Damage to installations

    Damage to installations

  • Hotspots


  • Micro-cracks


  • Breakage of glass (module)

    Breakage of glass (module)

Consequential damage

There is a danger of failures due to overheating, thermal overload or over-voltage, culminating in risk of fire for adjacent media. The formation of a flashover at the DC cabling or the PV module is a frequently underestimated problem. A direct current of up to 1,000 volts may occur in the module strings.

Hazards when touched

The flow of electricity through the human body is dangerous. It may happen e.g. when touching exposed parts that are lacking insulation. A flashover occurs as soon as the hand is pulled away. High temperatures result in severe burns, and electrolytic effects in organ damage. The flashover cuts off when the gap between the part and the hand increases.

Our methods and tools

Characteristic measurement

The measurement of the IV-curve of a PV module or string is an effective and more exact method of calculating the performance of a PV system and finding errors. The measured values are converted to STC values of the modules under consideration of sunlight level, temperature and tilt angle.

Contactless measurement

The current inside the individual substrings can be indicated acoustically and visually by moving a sensor over the modules’ busbars. This method can be utilised at low levels of sunlight and a higher cloudiness. With its ability to catch currents from as low as 1.0 A, it is an alternative to thermography.


real-time snapshot or video of the PV system can be taken with a 640x480p thermal imaging camera and a real image camera. The cameras can be mounted on a multicopter or a pole. The performance and documentation derives from the VATh-Directive for electrical thermal imaging. It depends on the weather (cloudiness).

  • Characteristic measurement

    Characteristic measurement

  • Contactless measurement

    Contactless measurement

  • Thermography


Our Services

PV system plausibility check

Error check and location for PV systems

PV system optimisation

Preparing expert opinions (TÜV Perscerf)

Annual monitoring and checks

Studies on PV system regeneration

Solar Diagnose – a service by Ingenieur-Büro Maus

The first plans for renewable energy systems were made in 1993. Wind power plants were initially in the centre of attention, PV systems joined them in 2004. An educational background as an electrical engineer and metal worker turned out to be a solid basis for the planning, operation and maintenance of renewable energy systems. Long-term experiences in operating wind power and photovoltaic systems are the foundation for a deep understanding of defect analysis, which has been recognised by a TÜV certification as “Expert for photovoltaics”.