PV commissioning after installation: checklist for an independent inspection

A new PV system is installed, the inverter is running, the first kilowatt-hours have been generated. But is the system really correctly installed? Installation errors, suboptimally wired strings, incompletely seated connectors and initial hotspots from handling damage are more common at commissioning than operators and even installers suspect. This guide explains what a complete PV commissioning inspection involves, which standard applies – and why thermography is the indispensable final step.

Why an independent acceptance inspection makes sense

For construction projects of all sizes the acceptance inspection is the formal act by which the client confirms that the work has been completed in accordance with the contract. For PV systems many commercial operators lack this awareness – the system is running, so it is finished. This attitude is economically risky.

Installation errors not detected at acceptance can cause yield losses over the entire operating life of the system. A suboptimally wired string with 5% yield reduction costs several thousand euros in lost income over 20 years for a 200 kWp system. An incompletely seated MC4 connector can become a fire risk within years.

Furthermore the warranty period only begins with the acceptance inspection. Anyone who does not carry out a written acceptance inspection often has difficulty proving the exact start of the period. And: many insurance policies for PV systems require the system to have been erected and accepted in accordance with recognised technical rules. A missing acceptance log can lead to payout reductions in the event of a claim.

Which standards apply – DIN EN 62446 and IEC TS 62446-3

For the acceptance and initial inspection of PV systems in Germany the DIN EN 62446-1 "Photovoltaic systems – requirements for testing, documentation and maintenance – Part 1: grid-connected systems" applies. It defines which measurements, documentation and inspections must be carried out at commissioning. The acceptance log produced to this standard is the core technical document of the system.

Die IEC TS 62446-3 "Thermographic inspection of PV modules and systems" supplements the initial commissioning inspection. It defines the measurement conditions, classification methods and report requirements for the thermographic inspection. An acceptance inspection that takes both standards into account delivers the most complete technical picture of a new system.

In addition to these product standards the following apply to the electrical parts of a PV system: DIN VDE 0100-712 (electrical installations with PV supply) and VDE-AR-N 4105 for the grid connection. Conformity with these standards is confirmed by the qualified electrician as part of the electrical acceptance inspection.

The complete acceptance checklist

The following checklist is based on the requirements of DIN EN 62446-1 and IEC TS 62446-3. It is divided into five areas:

Documentation and acceptance log

The acceptance log per DIN EN 62446-1 is the central document of the system. It contains all measurement results, inspection findings and signatures of the installer and operator. This document should be archived permanently – it is the basis for all subsequent warranty and insurance claims.

The log should contain at minimum: system data (location, capacity, configuration), measurement results per string, inspection result for all protective devices, list of documents handed over, date of commissioning and signatures. Many insurers require a copy when the contract is concluded.

The thermography report per IEC TS 62446-3 supplements the acceptance log with the thermal condition of the system at the time of commissioning. This initial condition is valuable for subsequent comparative inspections: when new anomalies appear in an inspection after three years, comparison with the first report can prove they were not already present at acceptance.

Thermography as the final step of the acceptance inspection

The electrical measurements per DIN EN 62446-1 check whether the system functions correctly. Thermography checks whether it is fault-free and safe . Both inspections complement each other and neither can replace the other.

Typical findings of the initial thermographic inspection at acceptance are: hotspots from handling damage during transport or installation, connectors with increased contact resistance from incomplete seating, individual modules with deviating thermal behaviour from cell mismatch and overheating at terminals in the junction box from incorrect tightening torque. These findings at acceptance are usually still under the installer's warranty and can be remedied at no cost to the operator.

The same finding that would be remedied free of charge at acceptance under warranty costs the operator money after the deadline has expired. This makes commissioning thermography one of the most economical investments in the lifecycle of a PV system.

Typische Installationsfehler – was bei der Abnahme häufig gefunden wird

The practice of acceptance inspections reveals a recurring picture. Most frequently found: incompletely seated MC4 connectors (particularly for systems completed under time pressure), individual modules with incorrectly polarised junction boxes (often still electrically functional but with heat development), strings with too high open-circuit voltage from incorrect module numbers and corrosion protection deficiencies on the mounting structure that only become visible after years.

Less common, but with high damage potential: incorrectly sized fuses in string boxes, missing or incorrectly installed bypass diodes in individual modules and insulation defects on cables from chafing at sharp sheet metal edges of the mounting structure.

Abnahme und Gewährleistung – der direkte Zusammenhang

The acceptance inspection is the legal starting point of the warranty period. From this date the five-year period for structures runs (§ 634a BGB). What is found and documented before acceptance is clearly classified as a defect at handover – the installer must rectify it at their own expense. What is only discovered after acceptance must be claimed by the operator as defects and, where necessary, proven to have already been present at handover.

A complete acceptance log with a thermography report as an attachment provides this evidence. It documents the exact condition of the system on the day of handover – without gaps and geo-referenced at module level. This depth of documentation cannot be achieved by any other method.

Frequently asked questions