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Owing to the well-known temperature dependence of photovoltaic (PV) module performance, it is important to correct the performance ratio with respect to temperature. In this study, temperature coefficients given by the manufacturer for three different PV cell technologies are compared with experimentally obtained temperature coefficients for a PV park situated in southern Norway. Three irradiance estimation methods are used to calculate these experimental temperature coefficients. The results show that they can differ significantly from the ones provided in the datasheet of the manufacturer for all three PV systems, but whether the temperature coefficient value increases or decreases depends on the systems and/or the irradiance estimation method. Furthermore, by analyzing nine clear sky days at different times of the year, it is found that the seasonality of the performance ratio can be significantly reduced when employing the experimental temperature coefficient rather than the datasheet temperature coefficient. As such, it may be more relevant to correct the performance ratio with experimental temperature coefficients rather than with the temperature coefficient from the system datasheet, especially for systems that experience large temperature differences. It is also found that the irradiance estimation method can significantly impact the experimental temperature coefficient. This study shows that the choice of irradiance estimation method and temperature coefficient can affect the performance interpretation of solar PV systems and must then be considered carefully.