How Meteonorm Weather is Generated
Meteonorm weather is a commonly-used weather source for international locations. This satellite weather source provides a uniform methodology for calculating irradiance, and will always be within 10 miles of the design site. However, it can cause some confusion due to the way it is generated in HelioScope.
HelioScope obtains monthly irradiance values from Meteonorm, then stochastically generates hourly values from that data. While the hourly level data is simulated, the sum of the hours in a month always adds up to the monthly irradiance value we were given. Since this is a “synthetic” year, we indicate the year as “2021”, to indicate that the hourly weather values do not represent a specific measurement source. This is in contrast to ground-based “TMY” files where the annual weather file is based on aggregating months from specific years (you can read more detail on that process here: http://help.helioscope.com/article/59-tmy-weather-file-primer)
Meteonorm uses irradiance data is from 1991-2010, and temperature & wind speed data is from 2000-2009. HelioScope uses Meteonorm version 7.1.
You can find an in-depth overview of the methods Meteonorm uses to generate this data here: https://meteonorm.com/assets/downloads/mn73_theory.pdf