The pyranometer measures solar radiation flux density from a 180 field of view angle. it normally measures radiation in 300 to 2800 nm bandwidth. Thermopile pyranometers are frequently used in Solar Power Plants, meteorology, climatology, climate change research, and building engineering physics. Pyranometers are an important part of the solar power plants to monitor the R of a solar power plant. In a solar Power plant, the pyranometers are usually installed horizontally for measuring GHI and in the plane of array for measuring GII. A pyranometer may be classified either as a Class A (or Secondary Standard), Class B (or First Class), or Class C (or Second Class).