Method for detecting power production degradation of solar power plants, wherein a) from at least one photovoltaic module of a solar power plant or from the solar power plant due to power plant measurements (PPME) of module/plant-internal parameters inter alia the measurement of an irradiance I as a first parameter and a temperature T as second parameter during a recurring, in particular periodic, time interval (ti) irradiance measurement data (MD I,ti) and temperature measurement data (MD T,ti) are collected and stored, b) related to the measured irradiance I per time interval (ti) stored irradiance reference data (RD I,ti) are used, characterized by: c) Selecting a time period (tp) with tp≥n·ti and n ∈ N, d) executing an equivalence model for the time period (tp) by - accessing to -- irradiance evaluation data (ED I,tp) including irradiance measurement data (MD I,ti=1, MD I,ti=2,... MD I,ti=n) of the stored irradiance measurement data (MD I,ti), -- irradiance comparison data (CD I,tp) including irradiance reference data (RD I,ti=1, RD I,ti=2,... RD I,ti=n) of the irradiance reference data (RD I,ti) and -- temperature evaluation data (ED T,tp) including temperature measurement data (MD T,ti=1, MD T,ti=2,... MD T,ti=n) of the stored temperature measurement data (MD T,ti), - calculating an equivalence function f (ED I,tp, ED T,tp) to determine a model equivalence between the irradiance evaluation data (ED I,tp) and the temperature evaluation data (ED T,tp) on the one hand and the irradiance comparison data (CD I,tp) on the other hand, e) estimating for the determination of the model equivalence a temperature compensation factor (β T), an irradiance compensation factor (β I) and a variability compensation factor (α I) with the stipulation that the temperature compensation factor (β T) and the irradiance compensation factor (β I) remain the same over a lifetime of the solar power plant and the only variable size is the variability compensation factor (α I), which is influenced by the power production degradation, f) evaluating or doing a trend analysis of an evolutionary course of the variability compensation factor (α I) being estimated accordingly over numerous time periods (tp) with constant or variable time durations. a) from at least one photovoltaic module of a solar power plant or from the solar power plant due to power plant measurements (PPME) of module/plant-internal parameters inter alia the measurement of an irradiance I as a first parameter and a temperature T as second parameter during a recurring, in particular periodic, time interval (ti) irradiance measurement data (MD I,ti) and temperature measurement data (MD T,ti) are collected and stored, b) related to the measured irradiance I per time interval (ti) stored irradiance reference data (RD I,ti) are used, characterized by: c) Selecting a time period (tp) with tp≥n·ti and n ∈ N, d) executing an equivalence model for the time period (tp) by - accessing to -- irradiance evaluation data (ED I,tp) including irradiance measurement data (MD I,ti=1, MD I,ti=2,... MD I,ti=n) of the stored irradiance measurement data (MD I,ti), -- irradiance comparison data (CD I,tp) including irradiance reference data (RD I,ti=1, RD I,ti=2,... RD I,ti=n) of the irradiance reference data (RD I,ti) and -- temperature evaluation data (ED T,tp) including temperature measurement data (MD T,ti=1, MD T,ti=2,... MD T,ti=n) of the stored temperature measurement data (MD T,ti), - calculating an equivalence function f (ED I,tp, ED T,tp) to determine a model equivalence between the irradiance evaluation data (ED I,tp) and the temperature evaluation data (ED T,tp) on the one hand and the irradiance comparison data (CD I,tp) on the other hand, - accessing to -- irradiance evaluation data (ED I,tp) including irradiance measurement data (MD I,ti=1, MD I,ti=2,... MD I,ti=n) of the stored irradiance measurement data (MD I,ti), -- irradiance comparison data (CD I,tp) including irradiance reference data (RD I,ti=1, RD I,ti=2,... RD I,ti=n) of the irradiance reference data (RD I,ti) and -- temperature evaluation data (ED T,tp) including temperature measurement data (MD T,ti=1, MD T,ti=2,... MD T,ti=n) of the stored temperature measurement data (MD T,ti), -- irradiance evaluation data (ED I,tp) including irradiance measurement data (MD I,ti=1, MD I,ti=2,... MD I,ti=n) of the stored irradiance measurement data (MD I,ti), -- irradiance comparison data (CD I,tp) including irradiance reference data (RD I,ti=1, RD I,ti=2,... RD I,ti=n) of the irradiance reference data (RD I,ti) and -- temperature evaluation data (ED T,tp) including temperature measurement data (MD T,ti=1, MD T,ti=2,... MD T,ti=n) of the stored temperature measurement data (MD T,ti), - calculating an equivalence function f (ED I,tp, ED T,tp) to determine a model equivalence between the irradiance evaluation data (ED I,tp) and the temperature evaluation data (ED T,tp) on the one hand and the irradiance comparison data (CD I,tp) on the other hand, e) estimating for the determination of the model equivalence a temperature compensation factor (β T), an irradiance compensation factor (β I) and a variability compensation factor (α I) with the stipulation that the temperature compensation factor (β T) and the irradiance compensation factor (β I) remain the same over a lifetime of the solar power plant and the only variable size is the variability compensation factor (α I), which is influenced by the power production degradation, f) evaluating or doing a trend analysis of an evolutionary course of the variability compensation factor (α I) being estimated accordingly over numerous time periods (tp) with constant or variable time durations.