Test conditions and project use
What is the difference between STC values and real project conditions?
Read photovoltaic module STC values as standardized comparison data rather than a direct prediction of field output.
Short answer
Standard test conditions (STC) provide a common laboratory reference for comparing module nameplate values. Field conditions change with irradiance, temperature, spectrum, angle, soiling, shading and system losses, so project output requires a separate energy model.
Test conditions and project use
What STC standardizes
STC specifies irradiance of 1000 W/m², cell temperature of 25 °C and the AM1.5G reference spectrum. Cell temperature is not ambient air temperature. This provides a common rating basis, subject to the stated test method and measurement uncertainty.
Why the field is different
Module temperature and incident irradiance vary through the day and year. Orientation, shading, dirt, mismatch and electrical losses also affect system behavior.
How to use both correctly
Use STC fields for product identification and electrical inputs, then use project weather, layout and system assumptions for energy assessment. Do not turn nameplate power into an annual-yield promise.
A conditions label for every electrical table
Copy the condition block with the value; a test-table label is part of the evidence.
- Rating record
- Model / bin / table name / front irradiance / rear irradiance when relevant / cell temperature / spectrum / measured field / page.
- Site record
- Timestamp / plane-of-array irradiance / cell or backsheet temperature and method / wind / shading / system losses. Ambient air temperature is a different field.
- Conflicting labels
- If document languages disagree on STC, NOCT or a bifacial test basis, preserve both labels and request issuer clarification before using the row.
Record template: replace prompts with project evidence and retain unresolved items. It does not authorize purchase, installation or release.
Project checklist · Test conditions and project use
- Exact model and power bin
- Declared test condition
- Project weather data
- Layout, shading and soiling assumptions
- System-loss and energy-model inputs
FAQ
Frequently asked questions
Does STC power equal field output?
No. It is a standardized rating, while field output changes with operating conditions.
Can two STC ratings be compared?
Yes when the models, units and test basis are clear, but project fit still needs further review.
What predicts annual energy?
A project-specific model using weather, layout, equipment and loss assumptions.
Sunhorn
Turn the reading into a model-specific review.
Share the application, target power range, destination and order requirements so the exact datasheet can be checked against the project.