Hi all,
This is an interesting discussion, and reflects what we've observed as well in New Zealand. In the past we used Meteonorm, but when Meteonorm 8.0 was released we also noticed a significant increase in insolation.
Due to this, we did an analysis where we compared the output of PVSyst modelling using Meteonorm 7.x, Meteonorm 8, SolarGIS, historical recorded data from local weather stations, and data that was recorded on site at a completed project (both irradiance & energy output, for 1 year).
Our findings showed that when compared to the actual output of the solar farm for 1 year, using Meteonorm 8 overestimated the modelled output of the farm by more than 10%, whereas the older Meteonorm was within 2%.
When the insolation estimate was compared to historical data from local weather stations, again Meteonorm 8 estimated significantly higher insolation compared to the measured & averaged historical data. In the end we chose to get a SolarGIS subscription, as their estimate was slightly lower than the measured historical average so it felt like a suitable conservative estimate for our commercial modelling.
