The definition of energy efficiency is simply to use less energy to perform the same task or produce the same result. The goal is to eliminate wasted energy. When a home or business is energy efficient, it uses less energy to heat, cool, and run appliances and electronics. An energy-efficient factory uses less energy to produce goods. When it comes to fighting climate change, energy efficiency is one of the easiest and most cost-effective ways to achieve Net Zero emissions of carbon dioxide through decarbonization. And since it aims to eliminate wasted energy, energy efficiency reduces costs.
The energy efficiency definition can involve calculating the ratio of output of performance (say, heating a building), a service (such as public transport), or goods (textiles, for example) in relation to the input of energy. For an economy-wide definition of energy efficiency, GDP is often compared to energy use, to measure what economists and governments call „energy intensity”.