Assessment of direct normal irradiance and cloud connections using satellite data over Australia

Australia has some of the best solar energy resources on the planet. With a Renewable Energy Target (RET) scheme designed to ensure that 20% of Australia's electricity comes from renewable sources by 2020, these resources are rapidly being developed. Although not yet widespread, Concentrating Solar Power (CSP) plants are expected to play a significant role in Australia's future solar-derived electricity. The variability of Direct Normal Irradiance (DNI) is largely responsible for the fluctuations in solar energy outputs from CSP plants. The temporal and spatial variability of DNI over Australia provides an assessment of the solar resource for future deployment of CSP plants. As such, this study analyses recent trends in the hourly solar DNI resource using data from 1990 to 2012 obtained from the Bureau of Meteorology (BOM). The deseasonalized DNI anomaly trends were significant over the west, southeast and northeast of Australia for all seasons. Knowledge of these trends is extremely important for siting and the prediction of CSP plant outputs. DNI increased by 50 W m−2 over west and southeast of Australia, whereas it decreased by 100 W m−2 over northeast of Australia - representing approximately +5% and −12% deviations from the long-term averages, respectively. Seasonal analysis also showed significant DNI trends, especially during the summer and winter. Most of the changes seen in DNI over Australia were modulated by changes in cloud amount over the region. The cloud amount obtained from the International Satellite Cloud Climatology Product (ISCCP) showed high negative correlations associated with DNI anomalies over Australia. The anomaly in cloud amount is highly correlated with the Southern Oscillation Index (SOI) obtained from BOM. The strengthening convective activity over Indonesia associated with strong La Niña events modulates cloud coverage teleconnecting towards northern Australia. This increases cloud cover and lowers the DNI significantly over these regions during the summer and autumn season. Although the change in DNI associated with cloud amount is clear, the effect of change in aerosols over these years still needs to be investigated.