When does solar thermography make sense?
A photovoltaic system rarely signals when something is wrong. Defective cells, overheated junction boxes and gradual degradation remain hidden – until yield noticeably drops or, in the worst case, a fire occurs. Solar thermography makes these invisible weak points visible. But when is an inspection really worthwhile, and what is the right moment?
What is solar thermography?
Bei der Solar Thermografie an infrared camera – either by drone or as a hand-held device – is used to measure the heat emission from solar modules during live operation. Defective components heat up more than functioning ones because electrical energy is converted into heat instead of being conducted as current. These temperature differences are made visible as a colour spectrum in the so-called thermogram.
The method is non-contact, non-destructive and without any operational interruption practicable. The system does not need to be shut down for the inspection – it actually needs to be running under load so that defects manifest thermally. A professional inspection to IEC TS 62446-3 provides a complete picture of all anomalies: from individual cell damage to bypass diode defects through to overheated junction boxes.
Wichtig: The quality of a thermographic inspection depends heavily on the measurement conditions. At least 500 W/m² solar irradiance, maximum 2/8 cloud cover and wind below 4 Beaufort are prerequisites for usable results. Correct timing is therefore decisive.
The 6 most important moments for a PV thermographic inspection
There is no universal answer as to exactly when solar thermography should be carried out. The answer depends on the age of the system, the operating conditions and the occasion. The following six situations almost always justify an inspection:
Thermography directly after installation uncovers errors that occurred during storage, transport and installation. Microcracks, incorrectly wired strings and faulty junction boxes otherwise remain undetected until the first yield report is disappointing. Important: as the client you still have warranty claims against the installer at this stage. A thermography report here forms the decisive documentation basis.
For commercial and industrial systems VdS-Richtlinie 2858 recommends a thermographic inspection of electrical systems annually. For PV systems an interval of 2–4 years has established itself in practice as economically sensible and technically sufficient. Gradual defects such as PID degradation or delamination develop slowly – regular monitoring prevents a small problem from becoming a costly failure.
Hail, storm and lightning can cause damage that is visually invisible. Microcracks often only fully develop weeks after a hail event, when the mechanical stress has continued through temperature changes in the material. Thermography after a weather event is in most cases a prerequisite for a successful insurance settlement – without a documented findings report many insurers refuse payouts.
When the monitoring shows a deviation of more than 5–10% from expected values and neither shading nor soiling is a plausible cause, thermography is the logical next step. It delivers a complete diagnosis within a single survey appointment – without dismantling, without operational interruption. Often several parallel defects lie behind what appears to be a small yield loss, each of which is barely noticeable on its own.
Most module manufacturers offer a performance warranty of 10, 12 or 25 years. Shortly before these periods expire it is worthwhile documenting the condition systematically. If defects are found that suggest a manufacturing fault, a thermography report can serve as a basis for warranty claims against the manufacturer. This opportunity passes irrevocably once the warranty period has expired.
Anyone buying or selling an existing system needs certainty about its actual condition. Thermography as part of Technical Due Diligence protects buyers from hidden defects and gives sellers a neutral expert report. For investors and funds acquiring entire solar farm portfolios thermographic condition assessment has now become standard.
What does solar thermography cost?
The cost of PV thermography depends on system size, location and desired scope of service. A flat-rate price is therefore not appropriate – the market does, however, move within understandable ranges:
Preisanfrage: The cost of PV thermography depends on system size, location and desired report scope. We will prepare an individual quote on request – contact us.
Für PV systems of all sizes we prepare a transparent quote – use our price calculator on the homepage for an initial estimate. The inspection includes the complete IR survey, identification of all conspicuous modules and a well-founded yield-loss estimate to IEC TS 62446-3.
Wirtschaftlichkeit: Undetected defects cause annual yield losses that add up considerably over the lifetime of a system. In most cases an inspection pays for itself quickly – provided detected defects are remedied.
What defects does PV thermography detect?
Solar thermography detects all anomalies that manifest thermally – i.e. through increased or reduced heat emission. These are essentially:
Hotspots occur when individual cells have increased resistance and convert energy into heat instead of electricity. They are the most common single cause of PV fires – from a temperature difference of 30 K from the surroundings, immediate action is required. Bypass-Dioden-Defekte create a characteristic pattern: a uniformly heated strip across a third or a quarter of the module, corresponding to the cell string division.
PID-Degradation (potential-induced degradation) shows itself through elevated edge temperatures and can cause up to 30% power loss with prolonged exposure. The insidious aspect: PID is reversible if detected early – but irreversible if left undetected for too long. Anschlusskasten-Defekte with overheated connectors or corroded contacts also become visible and are one of the most common causes of system failures.
Not detectable by thermography alone are fine Mikrorisse, which do not yet cause a thermally measurable failure. For evidence of early cell cracks a supplementary Elektrolumineszenzmessung is the more suitable method.
Solar Thermografie vs. Elektrolumineszenzmessung
Both methods are non-destructive and provide valuable information about the condition of solar modules – but they measure different things and are suited to different questions:
| Kriterium | Solar Thermografie | Elektrolumineszenz (EL) |
|---|---|---|
| Messprinzip | Infrarotstrahlung im Betrieb | Lumineszenzstrahlung im Dunkeln |
| Betriebszustand | System under load (in operation) | Anlage abgeschaltet (Nacht) |
| Erkennbare Defekte | Hotspots, PID, Bypassdioden, Kontakte | Mikrorisse, inaktive Zellen, Fingerunterbrechungen |
| Ertragsrelevanz | Direkt sichtbar (Wärme = Verlust) | Indirectly (not all cracks reduce yield immediately) |
| Drohnentauglich | Ja, großflächig möglich | Bedingt (erfordert absolute Dunkelheit) |
| Versicherungskonform | Ja (VdS 2858, IEC 62446-3) | Ergänzend, kein Standard |
In practice we recommend, when mechanical damage is suspected (hailstorm, transport damage), a Kombination beider Verfahren: thermography provides the overview and identifies all actively effective losses; EL measurement clarifies whether additionally structural damage is present that will worsen later.
Who benefits most from thermography?
In principle thermography is worthwhile for every PV system from approximately 20 kWp. The larger the system and the higher the economic value of the electricity generated, the clearer the cost-benefit calculation. An inspection is particularly worthwhile in the following constellations:
Gewerbliche Betreiber with rooftop systems from 100 kWp benefit particularly because they frequently optimise self-consumption and lost yield directly increases their energy costs. Solar farm operators and investors use thermography as a standard instrument in technical operations – often combined with biannual drone surveys and automated AI analysis.
Für Installers and EPC contractors a commissioning thermographic inspection is an effective quality assurance instrument: it documents the condition at handover without gaps and protects against later recourse claims. Insurers and expert witnesses use thermographic expert reports for claims settlement – particularly after hailstorms or lightning strikes.
For PV systems of all sizes we prepare a transparent quote by system size and location. Get in touch – we will prepare an individual quote.
Request inspection now →What is the best time of year for thermography?
Solar thermography is technically only usable when solar irradiance is at least 500 W/m² and the modules are operating at full load. In Germany this is reliably available from März bis September . Spring (March to May) has a practical advantage: the system has been through winter, any frost or snow-pressure damage is freshly formed and temperatures are still moderate – which benefits the contrast between hot and cold areas in the thermogram.
In summer irradiance values are consistently high, but so are ambient temperatures – this slightly reduces the thermal contrast for small defects. In autumn solar irradiance from October is no longer reliably sufficient for thermographic inspections. An Jahresende-Inspektion im Oktober is still possible if planned for sunny days; November to February are generally not suitable in Germany.
Häufig gestellte Fragen
The best season is March to September, when solar irradiance is reliably above 500 W/m². Within the season no time is fundamentally better than another – what matters is that the system is running at full load and the weather is cloud-free.
VdS guideline 2858 recommends thermographic inspection of electrical systems annually. For PV systems an interval of 2–4 years is common in practice and economically sensible – depending on system age, insurance requirements and operating conditions.
No. Solar thermography is carried out entirely without contact during live operation. The system actually needs to be running under load so that defects become visible through the waste heat generated in the infrared image. There is no yield loss whatsoever from the inspection.
From approximately 10–20 kWp thermography is economically worthwhile. Undetected defects cause annual yield losses that add up considerably over the lifetime of a system.
The cost depends on system size, location and desired report scope. Contact us – we will prepare an individual quote.
Solar thermography measures heat emission during operation and is particularly suited to hotspots, bypass diode faults and PID. Electroluminescence makes cracks and cell defects visible but requires darkness and the system to be shut down. Both methods complement each other – when microcracks are suspected we recommend a combination.
Conclusion
Solar thermography makes sense whenever you want to be certain that your PV system is delivering what it should. The six most important occasions – commissioning, regular maintenance, extreme weather, yield loss, warranty expiry and system transaction – cover most situations in which an inspection prevents damage or secures claims.
What is decisive is that the inspection is carried out by a qualified thermographer to IEC TS 62446-3 and that a structured report is produced – only then is the result insurance-compliant, court-admissible and usable as a basis for warranty claims.
Für PV systems of all sizes we will prepare you an individual quote. Contact us – we will clarify together whether and when an inspection of your system makes sense.