Method for determining the performance of components of a photovoltaic plant and/or of the photovoltaic plant comprising a plurality of strings, wherein in each of them a plurality of photovoltaic modules (AM, BM, CM) is connected in series, wherein the plurality of strings is connected to at least one inverter and wherein the method comprises the following steps: - generating of reference data; - generating of individual data; and - analyzing of the reference data and the individual data; wherein the step of generating individual data is performed in the same time span as the step of generating reference data and wherein the step of generating of reference data comprises the following steps: - determining a voltage over the first reference string (AM31 - AM37; BM21 - BM 27): and/or - determining of a current flowing in the first reference string; wherein the step of generating individual data comprises the following steps: - determining of a current flowing in one measurement string (AM21 - AM27; CM21 - CM27) of a plurality of measurement strings; and - determining of an estimated value of the incident solar radiation impinging on at least one photovoltaic module of the measurement string (AM21 - AM27; CM21 - CM27) during determining of the current in the respective measurement string; wherein the step of determining of the reference data and/or the step of determining the individual data comprises the step of determining the temperature of at least one photovoltaic module; wherein the step of generating individual data is performed successively for two further measurement strings of the plurality of measurement strings (AM21 - AM27; CM21 - CM 27), wherein the photovoltaic plant is controlled such that the components of the photovoltaic plant generate such a current and such a voltage that the components of the photovoltaic plant and/or the photovoltaic plant operates essentially at the point of maximal power; and wherein the step of analyzing the reference data and individual data comprises the following steps: - verifying, whether the reference data are during a predetermined time span within a reference tolerance range and/or whether the individual data are during a predetermined time interval within a individual tolerance range; and - if the reference data are within the predetermined time interval within the reference tolerance range and/or the individual data are within the predetermined time span within the individual tolerance range, determining the performance of the measurement strings of which the currents are determined during the predetermined time span. - generating of reference data; - generating of individual data; and - analyzing of the reference data and the individual data; - determining a voltage over the first reference string (AM31 - AM37; BM21 - BM 27): and/or - determining of a current flowing in the first reference string; - determining of a current flowing in one measurement string (AM21 - AM27; CM21 - CM27) of a plurality of measurement strings; and - determining of an estimated value of the incident solar radiation impinging on at least one photovoltaic module of the measurement string (AM21 - AM27; CM21 - CM27) during determining of the current in the respective measurement string; - verifying, whether the reference data are during a predetermined time span within a reference tolerance range and/or whether the individual data are during a predetermined time interval within a individual tolerance range; and - if the reference data are within the predetermined time interval within the reference tolerance range and/or the individual data are within the predetermined time span within the individual tolerance range, determining the performance of the measurement strings of which the currents are determined during the predetermined time span.