GVSOLAR:

ACCURACY AND VALIDATION

Validation of the global horizontal irradiation (GHI) estimation was performed using 223 meteorological stations equipped with pyranometers scattered across South America, Europe, Africa and Middle-East. The data is representative of most climatological conditions that are encountered in these areas and Greenvest is constantly updating its databases to have even greater geographical coverage and more stations to use for validation. The data used for validation are from 2004 until 2020 and down-sampled to a few years of data for each station, depending on the specific station availability during this data-frame.

In the table below, the percentiles of the Mean Absolute Error (MAE) in percentage are presented. As we can see, in the column "MAPE P50" the fiftieth percentile (or median) is shown, in the column "MAPE P75" the seventy-fifth percentile (or third quartile), etc. The three rows are named  "Station Cumulative", where the MAPE errors are calculated over the entire data associated with a specific station, "Monthly" and "Yearly", where the MAPE errors are calculated independently of the station over each month and each year, respectively, of the entire validation dataset.

Frequency
MAPE P90
MAPE P75
MAPE P50
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In the Heatmap below, the validation station distribution is presented

Map produced my Greenvest Solutions.

Cumulative errors per Validation Station

Here below, the distribution of the cumulative errors for each validation station is presented. The histogram in orange describes the mean percentage error of GHI, the one in green side shows the MAPE distribution, with the relative percentiles indicated by vertical dotted lines. As one can see, 5 stations appear to have a cumulative GHI error

The bias and standard deviation for the mean error for each station are:

Mean Bias for all sites: -0.05%

Standard Deviation:    ±0.69%

MPE_GHI_per_station_edited.jpg
MAPE_GHI_per_station_edited.jpg
Monthly errors

Here below, the distribution of the monthly errors of all validation stations is presented. The histogram in orange describes the mean percentage error of GHI, the one in green shows the MAPE distribution, with the relative percentiles indicated by vertical dotted lines. The few outliers on the histogram have been linked to 5 stations data which probably had a worse correlation with the predicted values due to either poor instrument calibration or shadowing of the instrument caused by e.g. a nearby tree. These data were nonetheless included in the validation analysis for sake of completeness.

The bias and standard deviation for the mean monthly error are:

 

Mean Monthly Bias:   0.09%

Standard Deviation: ±2.29%

MPE_GHI_monthly_edited.jpg
MAPE_GHI_monthly_edited.jpg
Yearly errors

Here below, the distribution of the yearly errors of all validation stations is presented. The histogram in orange describes the mean percentage error of GHI, the one in green side shows the MAPE distribution, with the relative percentiles indicated by vertical dotted lines. The same justifications can be attributed to the outliers as for the monthly errors, as explained above.

 

The bias and standard deviation for the mean yearly error are:

Mean Monthly Bias:   0.14%

Standard Deviation: ±1.70%

MPE_GHI_yearly_edited.jpg
MAPE_GHI_yearly_edited.jpg