A solar module is rated under controlled conditions
Nameplate power is normally stated at standard test conditions, not at the cell temperatures a roof reaches on a hot sunny afternoon. As module temperature rises, maximum power and operating voltage generally fall. The datasheet temperature coefficient expresses how strongly a particular electrical value changes relative to the reference temperature. Use the coefficient for the exact model; do not borrow one from a visually similar panel.
Cell temperature can be much higher than ambient air temperature
A weather app reporting 30°C does not mean the cells are operating at 30°C. Irradiance, wind, mounting height, roof material and rear ventilation affect module temperature. This is one reason hot, still roof conditions can reduce instantaneous power even when sunlight is strong. It does not mean a hot-climate solar system is a bad investment; annual yield depends on the whole weather profile, orientation, shading, system losses and available irradiance.
Voltage temperature behavior matters to inverter design too
Cold conditions raise open-circuit voltage, while hot conditions reduce operating voltage. Designers therefore check both ends of the temperature range: cold-weather Voc must stay below the inverter maximum input voltage, and hot-weather operating voltage should remain inside a usable MPPT window. The cold-weather voltage guide and MPPT string checklist cover those complementary checks.
Compare coefficients only after checking the rest of the module
A smaller absolute power-temperature coefficient can be useful in hot climates, but it should not override dimensions, current, voltage, mechanical loading, warranty, degradation, shade behavior and inverter compatibility. Model annual production with local weather data rather than multiplying one temperature coefficient into a simplistic savings promise. For commercial procurement, record the datasheet revision and exact model suffix so a later module substitution cannot quietly change the electrical assumptions.