During the processing of our Exemplary Weather and Energy Index (EWEI) analysis for the months of December 2021 and January 2022, we found some suspicious results when analysing the solar radiation data in Brisbane, which raised a few questions for us – by comparing the average Global Horizontal Irradiation (GHI) of that month with the average GHI of the Reference Meteorological Year (RMY) referred to December 2000, we noticed that the values for December 2021 were extremely low, particularly in the morning.
At first, we hypothesised there could be some shading happening on the weather station, caused by the recently built Queensland Children’s Hospital (QCH), which was built directly north east of the Children’s Health Research (CCHR) building, where the weather station was placed from which we used to receive data, thanks to our agreement with Queensland University of Technology (QUT). Nevertheless, while performing a shading analysis, we established that the QCH wasn’t shading the weather station on top of the CCHR building, and consequently we hypothesised that possible causes could be the calibration of the instrument or its maintenance. Access to the roof of the CCHR building requires harnessing and risk management procedure, because the weather station is on the roof of a plant room on the top of CCHR building, which could allow dust (or other material) building up on the instrument.
Since we were still finding the CCHR solar readings unintuitively low for the month of February 2022—even in a cloudier than usual summer—we investigated further by comparing the data with the daily total GHIs from the Bureau of Meteorology (BOM). The daily total GHIs for Brisbane CBD accessible through the BOM website were down around 10% relative to the reference year (January 2005) while for the same month, the CCHR readings were down circa 20%.
Consequently, to achieve a quasi-calibration based on the comparison with the BOM data, we modelled a data correction based on an orthogonal regression and a subsequent value capping based on the ASHRAE clear-sky model – below is shown the average solar GHI for the then last month of data (March 2022), compared to the RMYB, before the correction (RTY), after the correction (RTY corrected) and after the capping with the ASHRAE clear-sky model (RTY cap).
Finally, we continued to use this quasi-calibration for Brisbane in our EWEI analysis up until May 2022, when we subscribed to new sources of solar satellite data.