PV Acceptance Inspection by an Independent Expert

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 tests, there is no neutral control. In practice this shows up again and again at the same points:

• Test reports are filled in across the board without any actual measurements being taken.
• Documentation is missing or incomplete – string plans, circuit diagrams, measurement reports.
• Defects in cable routing, connectors or substructure are not raised because the inspector is the same party that caused them.
• The operator signs the acceptance without being able to judge the technical quality.

An independent inspection ensures that the operator does not only learn about problems once the system is already losing yield or poses a safety risk.

Which Standards Apply to PV Acceptance?

Testing a photovoltaic system is not left to the inspector's discretion. There are clear normative foundations:

A complete acceptance report refers to these standards and documents for each test point whether the requirement is met or a defect exists.

What Exactly Is Checked in an Independent PV Acceptance Inspection?

A serious acceptance inspection covers much more than a quick look at the roof. The scope of testing is divided into several areas:

1. Documentation Review

• Completeness of the system documentation according to DIN EN 62446
• String plan, circuit diagram, layout plan
• Data sheets (modules, inverters, substructure)
• The installer's commissioning report and test reports
• Declarations of conformity and certificates

2. Visual Inspection of the Mechanical Installation

• Module fixing and substructure (clamps, rails, roof hooks)
• Roof penetrations and seals
• Cable routing (bending radii, strain relief, UV protection)
• Connectors (MC4 compatibility, contact reliability)
• Labelling and warning signs

3. Electrical Tests

• Open-circuit voltage and short-circuit current per string
• Insulation resistance measurement (DC side)
• Earthing measurement and equipotential bonding
• Protective conductor test (AC side)
• Functional test of inverter, fuses and protective devices

4. Plausibility Check of the Design

• Does the string configuration match the plan?
• Is the inverter's MPP range correctly designed?
• Are modules installed uniformly or mixed?
• Does the actual layout correspond to the planning template?

The Acceptance Report: What Must Be Documented Under DIN EN 62446-1

The acceptance of a PV system is only complete once it has been documented in writing. The acceptance report (Abnahmeprotokoll) is exactly that document: it records the condition in which the system was handed over, which measured values were achieved and which defects were outstanding at the time of handover. If it is missing or incomplete, you will later lack the evidence of the system's original condition – and with it the most important lever against the installer and the insurer.

Mandatory Contents of a Test Report

A robust test and acceptance report according to DIN EN 62446-1 (internationally IEC 62446-1) contains at least:

• System and site data: operator, location, commissioning date, installed capacity, module and inverter types with serial numbers.
• String plan and wiring overview: traceable assignment of each string to inverter and MPP tracker.
• Insulation resistance per string – as a specific measured value in MΩ including test voltage, not as a blanket "OK".
• Open-circuit voltage (U_OC) and short-circuit current (I_SC) per string, each with irradiance and module temperature – without these boundary conditions the values cannot be assessed technically.
• AC-side test values: loop impedance, RCD tripping time and current, continuity of protective conductor and equipotential bonding.
• Result of the visual inspection with photo documentation of the critical points: connectors, cable routing, roof penetrations, substructure.
• List of defects with deadlines as well as date, name and signature of inspector and operator.
• Measuring instruments used, including proof of calibration – without this information a report is open to challenge in a dispute.

Is an Acceptance Report Mandatory?

A separate acceptance report is not expressly required by law. What is required, however, is the initial verification before commissioning according to DIN VDE 0100-600, and its results must be documented. In practice this means: without a test report, compliant installation has not been proven. Acceptance in the sense of German contract-for-work law (section 640 of the German Civil Code, BGB) is a second, separate step – it triggers the warranty periods, the due date of the final payment and the reversal of the burden of proof. That is exactly why nobody should sign an acceptance report before the system has been tested.

Installer's Report or Independent Test Report?

Both documents are called an "acceptance report", but their evidential value is very different:

Whether a report later holds up against the installer, insurer or court depends on the care taken in the documentation. What such an evidentially sound report costs is broken down under cost of an evidentially sound or court-ready PV expert report.

Practical Findings: Where Acceptance Reports Are Regularly Incomplete

Recurring weaknesses from expert practice:

• Measured values missing entirely: the report confirms "test carried out" but contains no figures – so it cannot be established afterwards whether anything was ever measured.
• Insulation measurement without test voltage: a value without the test voltage stated is technically worthless.
• U_OC/I_SC without irradiance and temperature: without boundary conditions, no deviation from the target value can be calculated.
• No string plan attached: later fault-finding and yield allocation become considerably more laborious.
• Operator signs before defects are remedied: acceptance has been declared, the defects remain – and the burden of proof now lies with the operator.

Documentation Duty: What the Operator Must Keep Permanently

Alongside the acceptance report, complete system documentation is part of the system's records. In particular, the following must be kept:

• declarations of conformity and data sheets of modules, inverters and optimisers,
• string plans, circuit diagrams and overview schematic,
• test and measurement reports of the initial verification and of all periodic tests,
• the grid operator's grid connection and commissioning documents,
• registration in the German Market Master Data Register (Marktstammdatenregister),
• installation and maintenance instructions as well as the maintenance and servicing log.

These documents are needed at the latest when a claim is settled or the system is to be sold or financed. If they are missing, reconstruction work arises that noticeably increases the price of a later expert report.

Typical Defects Found During Acceptance Inspections

In expert practice, certain defect patterns appear again and again. Many of them cannot be seen with the naked eye and only become apparent during systematic testing:

Many of these defects do not cause a total failure on their own – but in combination they can shorten the life of the system, reduce yield and jeopardise insurance cover in the event of a claim.

Cost of an Independent PV Acceptance Inspection

The costs depend mainly on the size of the system and the desired scope of testing:

For comparison: the total investment for a 10 kWp system in 2026 is typically €12,000 to €18,000. An independent acceptance inspection for €600 to €900 therefore corresponds to 3–7 % of the investment – and safeguards quality for the next 25 years.

Who Pays for the Expert Report? Cost Recovery from the Installer

One of the most frequent questions is: can I pass the cost of the independent acceptance inspection on to the installer? The answer is nuanced – but in many cases yes.

Basic Rule: The Client Pays First

Formally, the expert's fees are always borne by the client – i.e. the operator who commissioned the independent inspection. Initially, this is your investment in quality assurance.

When the Installer Has to Reimburse the Costs

If demonstrable defects are found during the acceptance inspection, the operator can, under certain conditions, claim the expert's fees from the installer as so-called pursuit costs (Verfolgungsschaden, also: consequential damage caused by a defect). Under German law, the legal basis for this derives from the law on contracts for work (sections 634, 636, 280 BGB) or from sales law (sections 437, 440, 280 BGB).

For reimbursement to have a prospect of success, three conditions usually have to be met:

1. There is a demonstrable defect. The expert report documents one or more technical defects that already existed at the time of handover.
2. The report was necessary to establish or enforce the claim. The defects were not readily recognisable to the operator as a layperson, or the installer had already failed to respond adequately to an informal notice of defects.
3. The costs are proportionate. The expert's fees must not be out of proportion to the extent of the defects found.

Typical Scenarios from Practice

Recommended Procedure

If the expert report reveals defects, ideally proceed in this order:

1. Written notice of defects to the installer – specific, with a deadline, referring to the expert report.
2. Set a deadline for remedying the defects – usually 2–4 weeks, depending on scope.
3. Claim reimbursement of the expert's fees – either as part of the request for remedy or separately as a damages claim.
4. If the installer does not respond: bring in legal support – the expert report forms the technical basis for legal enforcement.

Practical tip: document all communication with the installer in writing (email, registered letter). Verbal commitments are hard to prove in a dispute. The more cleanly the chain of expert report → notice of defects → deadline → response is documented, the better the chances of full cost reimbursement.

The Right Time for the Independent Acceptance Inspection

Timing is crucial. The independent inspection should take place within a clearly defined window:

1. The system is complete and ready for operation – all modules mounted, inverter configured, cabling finished.
2. Formal acceptance towards the installer is still pending – because the warranty period starts with acceptance.
3. The final invoice has not yet been paid in full – retaining 5–10 % until defect-free acceptance is customary under contract law and provides room for negotiation.

Ideally, commission the independent expert during the installation phase so that the appointment can take place promptly after completion. Waiting times of several weeks are not unusual for experts in demand.

How Does an Acceptance Inspection Differ from a Damage Assessment?

Both types of report can be carried out by the same expert. A thorough acceptance inspection in many cases avoids the need for a later damage assessment. An overview of all types of PV expert reports – and of what a PV expert report must contain – is given in the basic article.

Checklist: Prepare Before the Acceptance Inspection

So that the independent inspection can run efficiently, you should have these documents ready:

• ☐ Contract with the installer (including specification of works)
• ☐ Quotation and planning documents
• ☐ String plan and circuit diagram
• ☐ Data sheets of modules, inverters and substructure
• ☐ The installer's test report and commissioning report
• ☐ Photos of the installation (if available)
• ☐ Ensure access to roof and inverter
• ☐ Monitoring login details (if already set up)
• ☐ Final invoice (check payment status)

The more complete the documents, the more efficient – and therefore less expensive – the inspection.