CC BY 4.0Jochem, EberhardEberhardJochemBradke, HaraldHaraldBradkeDütschke, ElisabethElisabethDütschkeKlobasa, MarianMarianKlobasaWietschel, MartinMartinWietschelPlötz, PatrickPatrickPlötzFleiter, TobiasTobiasFleiter2024-10-222024-10-222024https://publica.fraunhofer.de/handle/publica/477858https://doi.org/10.24406/h-47785810.1007/978-3-031-66100-6_910.24406/h-477858Policy-oriented research of efficient energy use and energy demand during the last five decades developed from the scratch to a quite complex research field with many perspectives: new and improved energy-efficient buildings, vehicles, and production processes, structural changes in industry, income, rebound, and saturation effects. Although energy-efficient solutions were (and are) highly profitable, several obstacles prevent their full realisation. Energy policy "discovered" energy efficiency as the "fifth energy source" in the 1980s and labelled its policy priority after the increase of oil prices in the early 2010s by "efficiency first", although policy analysts may have doubts regarding the real energy policy and allocation of resources. The liberalisation of grid-based energy supply triggered a strong push for demand-side measures (flexible demand; energy services). Electricity demand models became much more dynamic in terms of time to match the increasingly fluctuating electricity supply and load shifting options. Climate policy since the 2010s induced a new wave of energy-efficient applications such as electric vehicles or heat pumps. Regarding the tough climate protection goals of a maximum temperature increase below 2.0 °C, more efficient energy use, conversion, and storage are likely to play a major role, particularly in using the large waste heat from useful energy applications.enEnergy demandEnergy efficiencyEnergy policyEnergy supplyEnergy systems modellingbook article