Quantifying Real-World Sources of Error in Redundant GHI Measurements

Many sources of pyranometer measurement uncertainty can be explicitly studied in the lab. These pointed, indoor studies work well to characterize some aspects of the instrument. However, contributions to measurement uncertainty of real-world conditions, such as instrument cleanliness and alignment, maintenance practices, and the inherent noise in the measurement are difficult to quantify. This study quantifies these sources of error by comparing the outputs of paired, collocated pyranometers in the field over the two-year period from 2021–2022 at each of 290 stations spread over a wide range of geographical locations in the United States.