**5. Energy efficiency**

Energy efficiency refers to the use of less energy to achieve maximum output, thereby reducing costs, producing less waste, and mitigating environmental impacts. Technological advancements in energy-efficient appliances and industrial processes drive improvements in energy efficiency. For example, LED (light emitting diode) lighting consumes significantly less electricity compared to traditional incandescent lighting while providing the same illumination. Adding thermal insulation material in walls and roofs can minimize heat loss in buildings and then maintain the desired temperature more efficiently. Utilizing fuel-efficient vehicles, such as hybrid and electric vehicles, reduces fuel consumption and emissions. Combined heat and power systems generate both electricity and useful heat that may maximize energy efficiency compared to separate generation of heat and power.

The efficiency of electric generation systems is particularly interesting as electricity serves as the backbone of industries, infrastructure, transportation, and communication in the world. The second law of thermodynamics puts an upper limit on achievable efficiencies of heat engines and then heat engine-based electric generators such as steam turbine generators, gas turbine generators, and internal combustion engine generators [3]. The energy efficiency of electric generators depends on various factors including the type of generators, operating conditions, design, and technology. Continuous efforts to improve efficiency through advancements in technology and operational practices are crucial for reducing energy consumption and minimizing environmental impact.
