Ocean-atmospheric drivers of wind and solar energy seasonal variability in tropical South America

South America is one of the regions with the highest renewable power share in its energy matrix. However, it is heavily affected during drought driven by El Niño/Southern Oscillation (ENSO) and the positive phase of the Atlantic Meridional Mode (AMM), since hydropower is the main source. Wind and solar energy are soaring due to economic development and as an alternative/complement to hydropower and fossil fuels. Nonetheless, they can be affected by climate variability modes and it is thus essential to determine the impacts of ocean-atmospheric modes on these two renewable energies. Our research focuses on understanding the links between climate modes and the seasonal variability of potential wind and solar generation. The understanding of the physical mechanisms driving renewable energy variability might be useful for improving sub-seasonal to seasonal forecasts and, hence, properly managing energy production and storage for the following months.

The analysis is also centred around three energy hubs (regions with multi-annual high production capacity of renewable energy). They are located near or on the north Caribbean coast, the east and east coast of Brazil, and the west coast of Peru and the Bolivian Altiplano. The research mainly uses composites of physically consistent interpolations (i.e. reanalysis ERA5) and some satellite-based observations from CLARA cloud cover (1980 - 2020). The ocean-atmospheric modes are defined using Sea Surface Temperature indices. It analyses the anomalies of wind speed, its direction and wind power density (WPD), but also Sea Level Pressure anomalies when climate modes are active. For solar energy, a capacity factor (CF) is calculated using an empirical method that considers the irradiance and the temperature of the panel (based on 2 m air temperature and incident radiation). To study the mechanisms producing its variability, we also analyse the atmospheric moisture transport (VIMF) and cloud cover. The ocean-atmospheric modes’ activation times are defined with Sea Surface Temperature indices.

We analysed the mechanisms of ENSO and of two climate modes in the Atlantic Ocean (the AMM and the Atlantic El Niño equatorial mode), as we discovered these modes can alter regional atmospheric circulation. Cross-equatorial wind anomalies – driven by the AMM – increase or reduce WPD depending on the region while also creating anomalous VIMF, convergence, and clouds, hence affecting the solar CF, in the north Caribbean and east Brazilian hubs. Not only does ENSO affect solar energy through atmospheric subsidence and reduction of cloud cover, but it also affects WPD attracting and accelerating winds to the equatorial east Pacific. The Atlantic equatorial mode (Atl3) is an important source of climate variability, but we discovered that its effects over the continent and the energy hubs are not so strong and widespread compared to those from the other two modes. We also found that solar and wind are not very often complementary, but they can potentially complement hydropower because stronger winds and less cloud cover are present during droughts.

Future research could focus on evaluating the impacts of sub-seasonal phenomena on renewable energy and their influence on predictability.