Quick Answer
The National Renewable Energy Laboratory (NREL), the International Electrotechnical Commission (IEC), and the North American Board of Certified Energy Practitioners (NABCEP) provide community resources for solar panel heat derating guidance.
Standardized Heat Derating Guidance
The International Electrotechnical Commission (IEC) 61730 standard outlines the requirements for photovoltaic (PV) module safety, including heat derating. According to the IEC standard, PV modules should be tested at temperatures of 125°C (257°F) and derated accordingly. A typical heat derating factor is around 0.75 for temperatures above 25°C (77°F).
Derating Curves and Temperature Coefficients
Derating curves and temperature coefficients are used to calculate the reduced power output of a solar panel at elevated temperatures. The IEC 61730 standard recommends a maximum power temperature coefficient (MPTC) of -0.5%/°C for crystalline silicon modules. This means that for every degree Celsius above 25°C, the power output will decrease by 0.5%. PV module manufacturers often provide derating curves and temperature coefficients in their datasheets.
Community Resources and Tools
The National Renewable Energy Laboratory (NREL) offers a PVWatts calculator tool, which includes heat derating functionality. The PVWatts calculator uses a standard heat derating curve to adjust the power output of a solar panel based on temperature. Additionally, NABCEP provides guidance on heat derating practices for PV installers and engineers. The NABCEP heat derating guidance recommends using a derating factor of 0.9 for temperatures between 25°C and 40°C (77°F and 104°F).
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