Pyranometer- Why to measure accurate solar irradiance ?

The Solar Radiation Sensor, or solar pyranometer, measures global radiation, the sum at the point of measurement of both the direct and diffuse components of solar irradiance. In-plane irradiance received by the PV array is one of the most important and significant factors that directly impacts the PV Performance. Irradiance must be measured accurately to determine your optimal PV performance ratio.