Reporting of irradiance modeling relative prediction errors

Metrics used in assessing irradiance model accuracy, such as root mean square error and mean absolute error, are precisely defined. Their relative (%) counterpart, however, can be subject to interpretation and may cover a wide range of values for a given set of data depending on reporting practice. This note evaluates different approaches for the reporting of relative metrics quantifying the dispersion accuracy of a model and formulates recommendations for the most appropriate approach.