Solar PV Temperature Coefficient

The temperature coefficient of maximum power measures how a solar module's peak electrical output changes when cell temperature changes by 1°C. For crystalline-silicon modules it is normally negative, so hotter cells produce less power and operate at lower conversion efficiency under the same sunlight.

Why efficiency falls as temperature rises

Higher temperature slightly narrows silicon's band gap and greatly increases the semiconductor's reverse saturation current. Consequently, open-circuit voltage falls appreciably, while short-circuit current rises only slightly. The voltage loss dominates, reducing the fill factor, maximum power and electrical efficiency.

Reading the temperature coefficient

Manufacturers express the coefficient, γ, in % per °C. Near standard operating conditions, output is approximated as P(T) = P25[1 + γ(Tcell - 25°C)]; because γ is negative, every degree above 25°C cell temperature lowers maximum power. For example, a coefficient of -0.4% per °C implies about 8% lower peak power at 45°C than at 25°C, at unchanged irradiance.

• Standard test ratings use 1,000 W/m² irradiance, 25°C cell temperature and the AM1.5 reference spectrum.
• The relevant temperature is the cell or module temperature, not merely the surrounding air temperature.

Practical implications

Module temperature depends on solar irradiance, ambient temperature, wind and mounting ventilation. Designs that improve rear-side airflow or remove heat help preserve voltage and energy yield; poorly ventilated modules generally operate hotter. Temperature affects instantaneous conversion efficiency, while actual electricity generation also depends on irradiance, shading and electrical losses.