Agri-PV Inspection: Thermography for Agri-Photovoltaic Systems

Agri-PV – the combination of agricultural use and photovoltaics on the same area – is one of the fastest-growing segments in the German solar market. The special structural characteristics of agri-PV systems also present new challenges for thermographic inspection. This article explains what operators and planners need to know about inspecting agri-PV systems.

Was ist Agri-PV?

Agri-PV denotes photovoltaic systems constructed so that the agricultural land beneath or beside them can continue to be productively farmed. The solar modules are typically mounted on elevated frames (usually 3–6 m clearance height) or installed vertically to allow the passage of machinery and animals.

In Germany the EEG and various federal state programmes support agri-PV with supplements to the feed-in tariff – provided the system meets defined criteria for dual use. DIN SPEC 91434 defines minimum requirements for agri-PV systems in Germany.

Types of agri-PV systems

Überspannende Anlagen (Overhead-Agri-PV): The most common form. Modules are mounted horizontally or at a slight tilt on tall frames, with crops grown or animals kept underneath. Typical applications: berry bushes, vegetables, grazing for sheep and cattle.

Vertikale Bifazial-Anlagen: Modules are installed vertically (east-west orientation) in rows between which arable farming with standard machinery can take place. This form enables maximum area efficiency and is used particularly for cereals and oilseed rape.

Interrow-Systeme: Modules are installed at lower mounting height between the crop rows. Common for vines, orchards and specialist crops.

Inspection characteristics for agri-PV

Agri-PV systems have several characteristics compared with conventional ground-mounted systems that make thermographic inspection more demanding:

Erhöhte Modulhöhe: In overhead systems the modules hang 3–6 m above the ground. This changes the optimal drone flight distance and thereby the IR camera calibration. We adapt our flight parameters to the system height.

Heat development under modules: Vegetation under the modules creates a different thermal background than ground cover. This requires experienced analysis to distinguish module heat from ground heat.

Maschinenzugang eingeschränkt: With ongoing agricultural operations inspection appointments must be coordinated with the farming cycles. A survey shortly after the harvest or before cultivation is ideal.

Bewuchs im Sichtfeld: Tall vegetation or fruit trees can shade parts of the system during the drone flight. For orchard agri-PV the survey during the leafless period (November–March) is preferable.

Bifacial modules and thermography

Many agri-PV systems – particularly vertical bifacial systems – use modules that generate electricity from both sides. When thermographically inspecting bifacial modules it must be noted that the rear side of the module also contributes to energy generation and can therefore be warm accordingly. Interpretation of thermograms requires more experience with bifacial modules, since normal operating heat on the rear side must not be confused with defects.

The standards-compliant measurement conditions per IEC TS 62446-3 also apply to bifacial modules. For vertical systems the requirements for the angle of solar irradiance differ from tilted systems – the inspection should take place at times of high direct irradiance on the active module side.

Drone flight over agricultural areas

The same legal regulations apply to drone flights over agri-PV systems as for other ground-mounted systems. It should be noted that agricultural land can have special requirements for drone overflights even outside nature conservation areas – particularly with free-range animal keeping. Chickens, sheep and cattle can be stressed by low-flying drones.

We coordinate inspection appointments at systems with animals so that the animals are kept away from the system before the drone flight. For sheep and cattle a 30-minute acclimatisation time is generally sufficient. For sensitive poultry keeping we recommend the inspection outside the animals' main activity times.

Inspection with grazing animals and free-range keeping

Agri-PV with sheep grazing is the most common combination in Germany – sheep keep the vegetation under the modules short and are easy to manage. For such systems we recommend the thermographic inspection at appointments when the sheep can be briefly led out of the system. This must be arranged with the operators in advance.

Damage from animal biting on module cables and connectors is more common in agri-PV with animal access than in conventional ground-mounted systems. Such damage leads to characteristic thermal anomalies that are reliably captured in the Complete package with hand thermography of the ground string infrastructure.

Recommended intervals for agri-PV

For agri-PV systems we recommend thermographic inspection on an annual cycle rather than the usual 2-year recommendation, due to the increased mechanical stress (agricultural machinery vibration, animal access, climate stress from vegetation). The first inspection should take place immediately after commissioning as an acceptance inspection to document the initial condition.

For the EEG subsidy requirements the annual inspection should be entered in the operating log and the reports archived – they are part of the documentation obligations for subsidised agri-PV systems.

Standards and subsidy requirements

For agri-PV in Germany the DIN SPEC 91434 applies as the basic technical standard. It defines the minimum requirements for dual use and is a prerequisite for the EEG special subsidy. For thermographic inspection the IEC TS 62446-3 remains the governing standard – regardless of system type.

Important for operators receiving EEG subsidies: regular technical documentation is part of the operator obligations. A standards-compliant thermography report every 1–2 years is the safest documentation basis.

Frequently asked questions