Method for determining the power loss of a planar photovoltaic assembly comprising one or more strings of photovoltaic modules, each string comprising at least one photovoltaic module, the strings being connected in series and/or in parallel between a positive terminal and a negative terminal, the method being implemented by an electronic device for determining the power loss of a planar photovoltaic assembly, and comprising the following steps, for a current state of said planar photovoltaic assembly: - detection of the presence or absence of a fault within each photovoltaic module of said photovoltaic assembly; - depending on the result of said detection, formation of two groups of photovoltaic modules comprising a first group G of fault-free photovoltaic module(s) and a second group D of faulty photovoltaic module(s), - for each healthy photovoltaic module(s) of said first group G, estimation of the G estimated irradiance and the ambient temperature associated with said healthy photovoltaic module under consideration as a function of meteorological and/or satellite data; - estimation of the reference surface temperature of said photovoltaic assembly via a predetermined two-dimensional polynomial model, the two orders of which, respectively associated with each direction of the considered plane of said planar photovoltaic assembly, simultaneously minimise a mean square error criterion using the measured temperature of each healthy photovoltaic module(s) of said first group; - for each faulty photovoltaic module(s) of said second group, search for a predetermined number N neighbour of healthy neighbouring photovoltaic module(s) closest in physical distance to said faulty photovoltaic module under consideration; - determination of the power loss associated with said faulty photovoltaic module(s) using, for each faulty photovoltaic module(s) of said second group D: - the measured temperature of the faulty photovoltaic module under consideration; - the reference surface temperature estimated using said predetermined polynomial model obtained by using said healthy photovoltaic module(s) adjacent to said considered faulty photovoltaic module; - the estimated irradiance associated with said faulty photovoltaic module using neighbouring healthy photovoltaic module(s). - detection of the presence or absence of a fault within each photovoltaic module of said photovoltaic assembly; - depending on the result of said detection, formation of two groups of photovoltaic modules comprising a first group G of fault-free photovoltaic module(s) and a second group D of faulty photovoltaic module(s), - for each healthy photovoltaic module(s) of said first group G, estimation of the G estimated irradiance and the ambient temperature associated with said healthy photovoltaic module under consideration as a function of meteorological and/or satellite data; - estimation of the reference surface temperature of said photovoltaic assembly via a predetermined two-dimensional polynomial model, the two orders of which, respectively associated with each direction of the considered plane of said planar photovoltaic assembly, simultaneously minimise a mean square error criterion using the measured temperature of each healthy photovoltaic module(s) of said first group; - for each faulty photovoltaic module(s) of said second group, search for a predetermined number N neighbour of healthy neighbouring photovoltaic module(s) closest in physical distance to said faulty photovoltaic module under consideration; - determination of the power loss associated with said faulty photovoltaic module(s) using, for each faulty photovoltaic module(s) of said second group D: - the measured temperature of the faulty photovoltaic module under consideration; - the reference surface temperature estimated using said predetermined polynomial model obtained by using said healthy photovoltaic module(s) adjacent to said considered faulty photovoltaic module; - the estimated irradiance associated with said faulty photovoltaic module using neighbouring healthy photovoltaic module(s). - the measured temperature of the faulty photovoltaic module under consideration; - the reference surface temperature estimated using said predetermined polynomial model obtained by using said healthy photovoltaic module(s) adjacent to said considered faulty photovoltaic module; - the estimated irradiance associated with said faulty photovoltaic module using neighbouring healthy photovoltaic module(s).