Solar PV Underperformance
How much PV loses, why, and what it costs.
“The difference between segments is not that smaller installations have more faults. It is that nobody knows how many they have.”
Solar PV Underperformance 2026, section 8.2
30 years of operation: management decides, not technology
A reference 100 kWp plant on an industrial hall roof. The three scenarios differ only in how the plant is managed.
Underperformance against the investment model with 0.5%/year degradation. The model does not include a one-off outage for inverter replacement. Scenario C is an extrapolation.
What it costs over the whole lifetime
Value of unproduced energy over 30 years at 100 kWp and €0.11/kWh. The difference between active and neglected management is roughly €54k.
Study, section 6.2.
More frequent inspection, smaller loss
The strongest data point in the study. A difference of about 4 percentage points is the best available estimate of how much of the loss can be fixed.
Raptor Maps, Global Solar Report 2026. Correlation, not proven causation.
Why nobody sees the faults
Free monitoring from the inverter manufacturer reliably catches only a minority of causes of loss. Most faults do not look like faults in it.
| Problem | Frequency | Severity | Does inverter monitoring see it? |
|---|---|---|---|
| Inverter outage | High | High | Yes |
| String outage | High | Medium–high | Partly |
| Connector and DC cabling fault | High | Medium | No |
| Soiling | Very high | Low–medium | Not without a model |
| Gradual shading | Medium | Medium | Not without a model |
| Microcracks | High | Low, rising | No |
| Hot spot | Medium | Medium, safety-related | No |
| PID | Low–medium | High | Partly |
| Faulty bypass diode | Medium, rising | High, safety-related | No |
| Incorrect settings at commissioning | Medium | Medium | Not without a model |
Study synthesis, section 5.5.
A 250 kWp plant in numbers
Underperformance reduces revenue linearly, but fixed costs remain. At a CAPEX of €600/kWp.
| Indicator | No losses | 5% underperformance | 10% underperformance | 15% underperformance |
|---|---|---|---|---|
| Annual output | 275 MWh | 261.3 MWh | 247.5 MWh | 233.8 MWh |
| Annual loss | — | 1 513 € | 3 025 € | 4 538 € |
| Simple payback | 5.0 years | 5.2 years | 5.5 years | 5.8 years |
| 25-year loss | — | €37.8k | €75.6k | €113.4k |
Undiscounted, excluding operating costs. An illustration of scale, not a financial model of the project.
SourcesNREL PV Fleet Performance Data Initiative · IEA PVPS Task 13 · Raptor Maps Global Solar Report 2026 · kWh Analytics Solar Risk Assessment 2026 · Kiwa PI Berlin · SolarPower Europe · ERÚ
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