The document discusses energy use in buildings and electricity consumption. It begins by defining energy and power. It then discusses understanding energy use through examples of average kWh per day per person in different countries. It also discusses measuring ecological footprint. The document then focuses on understanding electricity consumption in buildings through energy modeling and case studies. It provides examples of electricity consumption data from Hong Kong for residential, office, all buildings, and renewable energy. Finally, it discusses different types of renewable energy sources like solar, wind, hydropower, and biomass that can be used in buildings.