Question regarding Irradiation data

[Bulent]

Hi 

we are designing rooftop projects in Turkey . When we prepare the PVSOL reports, we often encounter much lower specific yields than compared with simulations on same location with PVsyst, which puts us in a less preferred situation for our customers.

Comparing global irradiation data from SOlargis, your values for Turkey is always at least 10-15% lower.

Also when we compare the real production in same location with the output from PVSOL, we see that the real yields are at least %10 higher than PVSOL estimations.

Is this normal ? How could we change the global irradiation data which meteocontrol database provides with 10% up ? or any other suggestions ?

Best Regards

Bülent Aydın

[developer_mh]

Dear Bulent,

thank you for your question. In PV*SOL, we use climate data from the well-known climate data specialist Meteonorm, see here:

https://help.valentin-software.com/pvsol/2019/calculation/irradiation/climate-data/

PVsyst also uses Meteonorm, so in terms of irradiation data there shouldn't be any difference between PV*SOL and PVsyst. Do you have an example project where we can see PVsyst and PV*SOL energy yields side by side?

Often the differences in the energy yield come from the models that are used to calculate the irradiance on the tilted plane of the PV modules. These models can be modified in the program options under Options -> Program Options -> Project Options -> Simulation:

 

Regarding values from SolarGIS: Yes, it is not unusual that climate data values can vary within +- 15 % between the sources. SolarGIS uses mainly satellite data, if I remember correctly. Meteonorm uses mainly ground measurement stations in combination with satellite data. And then there is PVGIS which also uses satellite data and whose values differ both from SolarGIS and from Meteonorm.

See some details about the meteorological approaches here:

• SolarGIS: https://solargis.com/docs/methodology/solar-radiation-modeling
• Meteonorm: https://meteonorm.com/assets/downloads/mn73_theory.pdf
• PVGIS: https://re.jrc.ec.europa.eu/pvg_static/pvgis5.pdf

As you will soon realize, there is no true or false for climate data. Nor is there any "higher values are better". It depends on what you want to achieve. If you want to achieve a higher simulated energy yield than your competitor, yes, you might be willing to choose the data source with the highest irradiation for a given place. But what happens if this simulated energy yield is too high? Won't the customer be dissappointed? We think that on the long run, it will shed a negative light on the project planners and users of our software (and the whole industry), which is why we always try to provide simulations that are conservative, but still realistic.

The climate data of Meteonorm do fit nicely in this "conservative" concept, where the yield that we simulate is nearly always topped in reality. But of course, you are free to import any other climate data into our software and simulate with that.

A guide how to import climate data from other sources can be found here:

https://help.valentin-software.com/pvsol/2019/pages/system-type-climate-and-grid/meteosyn/#options

Hope that helps, kind regards,

Martin

 

 

[Bulent]

Dear Martin

Many Thanks for your reply.

Best Regards

Bülent