The concept of environmental sustainability aims to achieve economic development while achieving a sustainable environment. The inverted U-shape relationship between economic growth and environmental quality, also called Environmental Kuznets Curve (EKC), describes the correlation between economic growth and carbon emissions. This study assesses the role of agriculture and energy-related variables while evaluating the EKC threshold in 54 African economies, and income groups, according to World Bank categorization, including low income, lower-middle, upper-middle, and high-income in Africa. With 1990–2015 panel data, the results are estimated using panel cointegration, Fully Modified Ordinary Least Square (FMOLS), and granger causality tests. The results are: (1) The study validated the EKC hypothesis in the low-income, lower-, and upper-middle-income economies. However, there is no evidence of EKC in the full African and high-income panels. Furthermore, the turning points of EKC in the income group are meagerly low, showing that Africa could be turning on EKC at lower income levels. (2) The correlation between agriculture with CO₂ is found positive in the high-income economy. However, agriculture has a mitigation effect on emissions in the lower-middle-income and low-income economies, and the full sample. Also, renewable energy is negatively correlated with emissions in Africa and the high-income economy. In contrast, non-renewable energy exerts a positive effect on emissions in all income groups except the low-income economies.

Hydrogen production from wind power and energy storage from wind power are considered as effective measures to overcome the problem associated with wind curtailment. However, their further development is clearly constrained by the incurred costs. Hydrogen production from offshore wind power (HPFW), hydrogen production from onshore wind power (HPNW), and underground pumped hydro energy storage from wind power (UPHESW) are considered in this paper. This paper employs a life cycle cost analysis to calculate and compare the levelized costs of hydrogen production and energy storage in China. A sensitivity analysis is conducted to evaluate the influences of different factors on levelized costs. The results show that the levelized cost of HPFW is 1.44 times that of HPNW. The levelized cost of UPHESW is lower than that of traditional pumped hydro energy storage with the same installed capacity and also lower than that of UPHESW with the smaller installed capacity. The economic competitiveness between UPHESW and HPNW depends on the installed capacity of UPHESW. If it exceeds 453 MW, UPHESW is more economical. If it remains below 453 MW, HPNW is more economical.