A solar power generation system including a solar battery array comprising a plurality of solar battery strings connected in parallel, each solar battery string comprising a plurality of solar battery modules connected in series, the system comprising: a plurality of string measurement units that measure a current and voltage of each of the plurality of solar battery strings; an array measurement unit (7c, 7d, 7f, 7g, 7i) that measures a current and voltage of the solar battery array; a computer configured to calculate an electric power loss of each of the plurality of solar battery strings, and that detects a failure in each solar battery string, wherein the computer is configured to perform a process of acquiring information about an amount of change in solar radiation in each of predetermined time bands in a day, and extracting, from among the predetermined time bands of which the amount of change in solar radiation is smaller than a predetermined amount of change in solar radiation, a first time band indicating a minimum amount of solar radiation and a second time band indicating a maximum amount of solar radiation, a process of calculating, using a ratio of operation current and short-circuit current in the solar battery array, an expected electric power value of the solar battery string to be inspected in each of the first and second time bands, a process of calculating, from a measurement electric power value of the solar battery string to be inspected in the first and second time bands, the expected electric power value in the first time band, and the expected electric power value in the second time band, a first electric power loss in the first time band and a second electric power loss in the second time band, and a process of detecting, based on the first and second electric power losses, failure in the solar battery string to be inspected. the system comprising: a plurality of string measurement units that measure a current and voltage of each of the plurality of solar battery strings; an array measurement unit (7c, 7d, 7f, 7g, 7i) that measures a current and voltage of the solar battery array; a computer configured to calculate an electric power loss of each of the plurality of solar battery strings, and that detects a failure in each solar battery string, wherein the computer is configured to perform a process of acquiring information about an amount of change in solar radiation in each of predetermined time bands in a day, and extracting, from among the predetermined time bands of which the amount of change in solar radiation is smaller than a predetermined amount of change in solar radiation, a first time band indicating a minimum amount of solar radiation and a second time band indicating a maximum amount of solar radiation, a process of calculating, using a ratio of operation current and short-circuit current in the solar battery array, an expected electric power value of the solar battery string to be inspected in each of the first and second time bands, a process of calculating, from a measurement electric power value of the solar battery string to be inspected in the first and second time bands, the expected electric power value in the first time band, and the expected electric power value in the second time band, a first electric power loss in the first time band and a second electric power loss in the second time band, and a process of detecting, based on the first and second electric power losses, failure in the solar battery string to be inspected. a plurality of string measurement units that measure a current and voltage of each of the plurality of solar battery strings; an array measurement unit (7c, 7d, 7f, 7g, 7i) that measures a current and voltage of the solar battery array; a computer configured to calculate an electric power loss of each of the plurality of solar battery strings, and that detects a failure in each solar battery string, wherein the computer is configured to perform a process of acquiring information about an amount of change in solar radiation in each of predetermined time bands in a day, and extracting, from among the predetermined time bands of which the amount of change in solar radiation is smaller than a predetermined amount of change in solar radiation, a first time band indicating a minimum amount of solar radiation and a second time band indicating a maximum amount of solar radiation, a process of calculating, using a ratio of operation current and short-circuit current in the solar battery array, an expected electric power value of the solar battery string to be inspected in each of the first and second time bands, a process of calculating, from a measurement electric power value of the solar battery string to be inspected in the first and second time bands, the expected electric power value in the first time band, and the expected electric power value in the second time band, a first electric power loss in the first time band and a second electric power loss in the second time band, and a process of detecting, based on the first and second electric power losses, failure in the solar battery string to be inspected.