In this paper, the solar radiation reduction monitoring of Macao world heritage district photovoltaic system using Geographical Information System (GIS) - Google Earth and 920-MHz Ultra-High Frequency Radio Frequency Identification (UHF RFID) obstacle detection approach is presented. When the solar panel is tagged with UHF RFID tag, its tag antenna effective area can be significantly affected if there is obstacle placed between tag and reader. An experimental trial of tag's Received Signal Strength Index (RSSI) reports more than 6 dB difference with and without obstacle. This property is a simple and economic solution for photovoltaic system to detect obstacle shadowing or covering the solar panel and; efficient solar radiation reduction monitoring can be easily integrated with existing photovoltaic GIS platform demonstrated.