# Temperature Coefficient

Hi,

I'm new to the PV technology and just have a few questions about the "Efficiency" and "Temperature Coefficient".

1. I understand the Efficiency is calculated based on Maximum/Nominal Power  and incident radiation under STC. If the power output is 200 W for a 1 m2 panel under 1,000 w/m2 condition, the efficiency is 20%. I assume when operating under the actual weather condition when the solar radiation is 500 w/m2 on the panel surface, theoretically the panel output would be 500 W * 20% = 100 W, is this correct? Or efficiency actually has changed?

2. Temperature Coefficient only affects Maximum/Nominal Power, right? Use the example above, the Nominal Power is 200 W, efficiency 20%. Assuming the temperature coefficient is -0.5%/C. Assuming the weather condition is: 600 w/m2 incident radiation and the cell temperature is 45 C. Under this condition, the power loss would be -0.5%/C * (45 C - 25 C) = -10%. So the Nominal Power would now be 200 W * (1-10%) = 180 W. This is Nominal Power though. The actual panel output at this time would be 600w/m2 * 20% = 120 W. Is above logic all right?

Thanks in advance!

•   thanks for your question. Maybe  can help answer this one.

• In reply to Chris Detzel:

The logic is correct for a solar panel under standard test conditions: 1000 W/m2, 25°C, 1.5 air mass. However, this is an ideal scenario. Simulation tools are used in actual projects to account for non-ideal conditions, and you can input manufacturer data.

For an actual project you have to consider that solar radiation and AM values may change. The NASA Atmospheric Science Data Center is a useful resource where you can input coordinates to get radiation tables for any location.

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