efficiency Technology: general issues 18 History of engineering & technology 14 renewable energy 13 sustainability 12 energy efficiency 10 Research & information: general 9 electric vehicle 7 sustainable development 7 optimization 6 energy 5 genetic algorithm 5 COVID-19 4 biomass 4 data envelopment analysis 4 electric vehicles 4 energy consumption 4 energy saving 4 finite element method 4 hybrid electric vehicle 4 machine learning 4 mathematical model 4 microgrid 4 modeling 4 particle swarm optimization 4 social media 4 solar energy 4 torque ripple 4 CFD 3 Environmental science, engineering & technology 3