Errors in solar energy measurement

The poor quality of much solar energy data is argued on the basis of field trips to data collection stations and observation and calibration of instruments on station. Deterioration and discoloration of sensors, effects of unstable mounting and off-level tilt, moisture, obstructions of field of value, and consequent discrepancies with recalibrated values are reported. Comparisons of pyranometer characteristics (sensitivity, stability over a year, temperature readings, selectivity and linearity, errors) are tabulated for pyranometers grouped in three quality classes.