The global trend of renewable energy generation and the advent of the Internet of Things technology has popularized inexpensive integrated monitoring technology. Accordingly, the Renewable Energy Monitoring System (REMS) project, which monitors solar plants subsidized by National funds, has been expanding its target since 2018. Concurrently, the mandatory post-management system became effective in 2020 to strengthen the post-management system. The 3-sigma rule is used to determine the control chart for the normal operation of solar systems from the monitoring data. In this study, solar plants with normal operation within the control chart were suggested to be excluded from field investigation with a focus on the management of solar plants with abnormal operation outside the control chart to improve the overall investigation into inefficiencies in the mandatory post-management system. Improvements to the monitoring system operation plan were also suggested.