Bibliometric Systematic literature review 2 Bibliometrics 1 COVID-19 1 Conflict 1 Conflict management 1 Economics 1 Energy efficiency 1 Energy research 1 Environmental management 1 Epidemiology 1 Family business 1 Hotspots 1 Investments 1 Machine learning 1 Machine learning–based analyse (principle component analyse) 1 Machine learning–based analysis (principle component analysis) 1 Planning 1 Principal component analysis 1 Principle components analysis 1 Renewable energies 1 Renewable energy 1 Semantics 1 Smart energy systems 1 Solar power generation 1 Sustainable development 1 Visual analysis 1 Wind power 1