The Most Important Point First
The legally required inspection of a PV system before commissioning is generally carried out by the installer themselves. This means: the person who built the system also confirms its freedom from defects. An independent commissioning inspection by an external expert closes exactly this gap.
Why the Installer Should Not Also Be the Inspector
This is not an accusation against the industry but a structural problem: when the same company installs and inspects, neutral control is absent. In practice this repeatedly shows up at the same points:
- Test protocols are filled in as a formality without actual measurements being taken.
- Documentation is missing or incomplete – string plans, circuit diagrams, measurement reports.
- Defects in cable routing, connectors or substructure are not challenged because the inspector is identical with the person responsible.
- The operator signs the acceptance without being able to assess the technical quality.
An independent inspection ensures that the operator does not find out about problems only when the system is already losing yield or presents a safety risk.
Which Standards Apply for PV Commissioning?
The inspection of a photovoltaic system is not left to the discretion of the inspector. There are clear normative foundations:
| Standard / Code | Content | Relevance |
|---|---|---|
| DIN EN 62446 / VDE 0126-23 | Minimum requirements for system documentation, commissioning inspection and recurring inspections of grid-connected PV systems | Central standard for PV commissioning – defines inspection scope |
| DIN VDE 0100-600 | Initial testing of electrical installations (AC side) | Mandatory inspection before commissioning |
| DIN VDE 0100-712 | Installation requirements for PV power supply systems | Regulates requirements for cabling, protective measures and labelling |
| VdS 3145 | Guideline for electrical testing of PV systems (insurance-relevant) | Required by many property insurers as inspection basis |
| VDE-AR-N 4105 | Technical minimum requirements for connection and operation at low voltage | Grid connection and inverter configuration |
What Is Checked in an Independent PV Commissioning Inspection?
A serious commissioning inspection covers significantly more than a quick look at the roof. The inspection scope is structured in several areas:
1. Documentation Review
- Completeness of system documentation per DIN EN 62446
- String plan, circuit diagram, layout plan
- Data sheets (modules, inverter, substructure)
- Installer's commissioning protocol and measurement records
- Declarations of conformity and certificates
2. Visual Inspection of Mechanical Installation
- Module mounting and substructure (clamps, rails, roof hooks)
- Roof penetrations and sealing
- Cable routing (bending radii, strain relief, UV protection)
- Connectors (MC4 compatibility, contact security)
- Labelling and warning notices
3. Electrical Testing
- Open-circuit voltage and short-circuit current per string
- Insulation resistance measurement (DC side)
- Earthing measurement and potential equalisation
- Protective conductor test (AC side)
- Functional test of inverter, fuses and protective equipment
4. Plausibility Check of the Design
- Does the string configuration match the plan?
- Is the inverter MPP range correctly configured?
- Are modules uniform or mixed?
- Does the actual layout match the planning basis?
Typical Defects Found During Commissioning Inspections
Certain defect patterns appear repeatedly in expert practice. Many of them are not visible to the naked eye and only come to light during systematic inspection:
| Defect category | Typical findings | Risk |
|---|---|---|
| Documentation | Missing string plans, no measurement record, incomplete system documentation | Warranty enforcement significantly more difficult; insurance settlement complicated |
| Connectors | Mixed MC4 brands, incompletely engaged connections, incorrect crimping | Fire risk, yield loss, insurance issues |
| Cable routing | Cables lying on sharp edges, missing UV protection, incorrect bending radii | Insulation damage after 2–5 years, earth fault |
| String layout | Strings mixed in orientation, wrong length for inverter MPP range | Permanent yield shortfall of 5–20% |
| Substructure | Missing end clamps, incorrect module spacing, inadequate roof penetration sealing | Mechanical damage, leaks, wind uplift risk |
Costs and Who Pays
The cost of an independent commissioning inspection depends on the system size and inspection scope. For a typical domestic system (5–15 kWp) costs are in the low to mid three-figure range; for commercial systems (50–500 kWp) the cost is correspondingly higher.
If the inspection reveals defects that are attributable to the installer, the costs of the expert report can often be claimed as consequential costs from the installer within the warranty period. This should be assessed on a case-by-case basis – legal advice may be appropriate.
Commissioning Inspection vs. Regular Inspection
A commissioning inspection is carried out once before or at the time of formal acceptance of the system. Regular inspections (typically every 4 years according to DIN EN 62446) are separate and serve to check the ongoing condition of the system in operation.
FAQ
Is an independent commissioning inspection legally required?
No – the operator has no statutory obligation to commission an independent inspection. However, it is strongly recommended from a technical and warranty-law perspective. Without an independent inspection, defects existing at the time of handover can be difficult to prove retrospectively.
When is the right time for an independent commissioning inspection?
Ideally before the formal acceptance of the system from the installer. This allows defects to be documented before the warranty period starts running and before the operator has signed the acceptance protocol.
What happens if the inspection reveals serious defects?
The defects are documented in the expert report. You can then request remediation from the installer before acceptance – without having to pay the full invoice. If acceptance has already taken place, the documented defects form the basis for a formal warranty claim.
Email: info@gutachterpv.org