A PV yield assessment is the right tool when it is no longer about "gut feeling" but about substantiated evidence: quantifying the deviation, technically explaining the cause, calculating the yield impact and prioritising remedial measures. It is the key document that operators, insurers, lawyers and investors need when monitoring figures alone are no longer sufficient.
What Is a PV Yield Assessment?
A PV yield assessment is a technical expert opinion that systematically investigates why a photovoltaic system generates less electricity than expected. Unlike a simple monitoring report that merely shows deviations, a yield assessment provides a causal explanation: which technical, planning or operational factors are causing the yield shortfall? What is the monetary loss? What action must be taken?
The assessment is produced by an independent expert and is structured so that it holds up as evidence in court, with insurers and vis-à-vis the installer. It contains measurement data, references to standards, photo documentation and a traceable root cause analysis.
Yield Assessment Before Construction or in Operation?
The term "yield assessment" (Ertragsgutachten) is used for two different services:
- Yield forecast before construction: Simulation of the expected annual yield for a bank, investor or funding application. Here an economic viability analysis with a plausibility check of the forecast is usually the right instrument – especially for acquisitions or financing.
- Yield assessment in operation (yield shortfall): The system is running but delivers less than promised. Cause, responsibility and yield loss in euros are established in an evidentially sound manner. This is the subject of this page.
Common Situations Requiring a Yield Assessment
In practice, there are four frequent situations in which a PV yield assessment becomes necessary:
- Persistently below forecast: The system has been generating significantly less than projected for months or years. The operator suspects a technical defect but cannot substantiate it.
- Dispute with the installer: The installer declares yields to be "within normal range" while the operator records measurable losses. Without independent documentation, legal proceedings are difficult to win.
- Insurance claim / loss settlement: After storm, hail or lightning damage, it must be proven what proportion of the yield loss is attributable to the damage – and what was already missing beforehand.
- Purchase or sale of a PV system: Investors and buyers require an independent plausibility check of historical yield data before setting a purchase price.
Practical example: On a 750 kWp rooftop system, the yield was around 30 % below forecast. The cause was a faulty string design at the planning stage – proven per inverter and per string. Details in the yield shortfall case study.
Procedure: How a Yield Assessment Works
A structured PV yield assessment follows a three-stage process:
The end result is a written assessment with root cause finding, yield impact calculation and concrete action recommendations. This document is the basis for warranty claims, insurance settlement or out-of-court agreements.
What Does a Complete Yield Assessment Contain?
- Description of the system (kWp, year of installation, components, orientation/tilt)
- Evaluation of yield data with a target/actual comparison
- Irradiation analysis and comparison with meteorological reference data
- Technical root cause analysis per inverter, string or module
- Photo documentation of the defects or anomalies found
- Calculation of the monetary yield loss
- Assessment against technical standards (VDE, IEC)
- Recommended measures and prioritisation
What You Can Prepare (Saves Time and Cost)
- Yield data (daily/monthly), ideally per inverter/tracker
- Error logs / fault messages from the monitoring system
- System data (kWp, orientation/tilt, components, year of installation)
- String plan / layout plan (if available)
- Planning documents and the original yield forecast
- Information on changes in shading at the site (tree growth, new buildings)
Cost of a PV Yield Assessment
The cost of a PV expert for a yield assessment varies with scope: a simple data analysis without a site visit typically starts at €500–800. A complete yield assessment with site visit, measurements and documentation usable in legal proceedings ranges from €1,200 to €3,000 depending on system size. For large systems above 100 kWp, an individual quotation makes sense. Detailed pricing information can be found on our page on the cost of a PV expert report in 2026.
Frequently Asked Questions About PV Yield Assessments
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