Modelled Solar Irradiance Data Report

• IEA PVPS's latest study is on global irradiance data models to help the industry make better informed decisions about solar resource assessments
• Its exploration found that the most appropriate dataset might depend on site, climate, or continent of interest
• For DNI, the model errors and the differences between the various modelled data sets are much higher than for GHI

In a new study under task 16, the International Energy Agency Photovoltaic Power Systems Programme (IEA PVPS) explores global irradiance data models to provide a benchmark of model-derived direct normal irradiance (DNI) as well as global horizontal irradiance (GHI), saying it will help the solar industry make better informed decisions about solar resource assessments.

Writers studied the DNI and GHI data at the sites of 129 globally distributed ground-based radiation measurement stations, spread across the 7 continents of Africa, Asia, North America, Europe, South America, Australia and Antarctica.

Then they compared DNI and GHI estimates from 10 different solar radiation datasets, either in the public domain or commercial, against high-quality ground-based irradiance observations from these stations. Modelled data sets in this benchmark are called test data sets.

Calculations were done for various statistical performance parameters as mean bias deviation, root mean square deviation and standard deviation for each year and for all stations.

Analysts eventually found that the most appropriate dataset might depend on site, climate, or continent of interest. Also, model errors and the differences between the various modelled data sets are much higher for DNI than for GHI.

They do add that without a stringent quality control procedure, no real validation can be done, with the risk of obtaining invalid results.

"Based on this work, analysts can make an informed decision about which surface radiation model(s) and data provider(s) are most suited for their location and application," reads the study. "Furthermore, it is recommended that a similar benchmark be conducted for more reference stations, including sites over regions that are so far not covered well or at all."

IEA PVPS adds that future work will further analyze the expected positive impact of various post-processing methods or site-adaptation on the data evaluated in this benchmark.

The complete study titled Worldwide Benchmark of Modelled Solar Irradiance Data is available for free download on the IEA PVPS website.