Potential of Wind and Solar Energy Gerneration over West Africa in a Changing Climate

Abstract

Many West African countries are plagued with a poor electricity supply. However, an abundance of solar irradiance and sufficient wind speed over the region makes solar and wind energy attractive solutions to the problem, but there is a dearth of information on how ongoing global warming may alter the solar energy potential and wind power density over the region in the future. Moreover, there is a lack of information on how accurately numerical weather prediction models simulate the shortwave radiation flux over the region. This study thus investigates, on the one hand, the impact of climate change on photovoltaic power generation potential (PVP) and on wind power density (WPD) over West Africa under various global warming levels (1.5°C; 2.0°C; 2.5°C and 3.0°C) under the RCP8.5 climate change scenario. On the other hand, this study assesses the shortwave radiation flux over West Africa. For the PVP study, fourteen regional climate model simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) were analysed. Eleven multi-model multi-ensemble simulation datasets, also from the CORDEX project, were analysed for the WPD study. The model simulations for the reference climate (1971-2000) were compared with surface wind speed from weather stations data: Accra (1986 - 2000), Bobo-Dioulasso (1986 - 2016), Ouagadougou (1986 - 2016) and Tamale (1986 - 2000) and two examples of reanalysis data (ERA-INTERIM and ERA20C). In addition, this study also investigated how the Weather Research and Forecasting (WRF) model radiation schemes (Cam, Dudhia, Goddard, New Goddard and rrtmg) simulate the surface downwelling solar radiation (Rs) over West Africa. We modified the Dudhia shortwave radiation physics by making the water vapour absorption varies with temperature and pressure according to levels. Furthermore, we run a short-term simulation (one-year) with WRF different shortwave radiations schemes and a long-term simulation (thirty-years) with the WRF Dudhia shortwave radiation scheme and the modified one. All the WRF output were compared with satellite data (SARAH). The results show that the CORDEX simulation ensemble correctly captures the spatial distribution of climate variables (surface downwelling solar radiation, air temperature, wind speed and relative humidity) and PVP over West Africa, albeit with a few biases. The simulations and observations agree that PVP over West Africa varies from 8% along the Guinean zone to 25% over the Sahel zone and that the annual cycle of PVP is influenced by the seasonal variation of the monsoon system. The simulation ensemble projects a decrease (up to 3.8%) in PVP over West Africa in the future and indicates that the magnitude of the decrease grows with warming levels. The decrease in PVP is attributed to a decrease in Rs (solar dimming; up to 3 W/m2) and an increase in ambient temperature (up to 3.5°C) induced by global warming. A decrease in projected PVP is also projected over all the West African countries. Nevertheless, the spatial and temporal distribution of the PVP changes are more influenced by Rs changes than by Ts changes, such as at GWL1.5, an increase in PVP is projected over all zones during the rainy season when an increase in Rs is projected. A decrease in projected PVP is also projected over all the countries. Nevertheless, the maximum decrease in PVP projected over any country or zone in the region is less than 3.8% even at GWL3.0. Hence, the study suggests that ongoing global warming may have an influence on PVP over West Africa.