Peak vs real power of a solar panel: what the datasheet doesn't tell you
Your '410 W' panel almost never produces 410 W. The label is lab conditions (STC). Reality varies with hour, temperature, shading and dirt.
You buy a '410 W' panel. Plug it in, expect to see 410 W production. Perfect noon: you read 320 W. Were you ripped off? No. Label is nominal, reality is different. How it's measured.
STC: the lab conditions
Standard Test Conditions: 1000 W/sqm radiation, 77 °F cell temperature, AM 1.5 (standard atmosphere). These are datasheet conditions. Reproduced with xenon flash in isolated chamber. Almost never occur in nature.
NMOT: real conditions
Nominal Module Operating Temperature: 800 W/sqm radiation, 68 °F air, 2 mph wind. Closer to reality. Datasheet also includes NMOT power, 25-30% lower than STC. For a '410 W STC' panel: ~310 W NMOT.
Why you never hit STC
1) Radiation rarely reaches 1000 W/sqm (typical summer noon: 800-950). 2) Panel at 77 °F is impossible in full sun (always 105-150 °F). 3) Real atmosphere filters 5-10% more than ideal AM 1.5.
Capacity factor: the realistic metric
Capacity factor = real energy produced ÷ theoretical max energy. For PV: 14-22% by latitude. Central US: 19%. Sun Belt: 22%. Northern US: 14%. So your '410 W' panel produces ~750 kWh/year (not 3600 theoretical).
How to not get surprised
When sizing your install, don't use STC power to calculate consumption. Multiply by 1500 (USA average) kWh/kWp/year. That's actually useful. If your calculator uses STC and promises X, expect 65-75% of X.
Compare with temperature effect.
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