CC BY 4.0Hirzel, SimonSimonHirzelRohde, ClemensClemensRohdeBarkhausen, RobinRobinBarkhausenDurand, AntoineAntoineDurand2023-03-282023-03-282023https://publica.fraunhofer.de/handle/publica/437311https://doi.org/10.24406/publica-99910.24406/publica-999Given the limited availability of fossil resources, primary energy has been and remains an important indicator for assessing the efficiency of an energy system. As long as the energy supply was mainly based on energy carriers where the energy was stored by chemical bonds, this consideration was mostly straightforward. However, with the growing importance and diversity of renewable energies, the concept of primary energy is increasingly reaching its methodological limits. Only when you are aware of this, you can properly perceive the different uses of primary energy as an indicator. In the series ENERGY EXPLAINED by the Fraunhofer Institute for Systems and Innovation Research ISI, scientists investigate complex issues from the field of energy research and offer a clear and concise introduction to the respective topics.enPrimary energy factorPrimary energyFinal energyEnergy carrierFossil fuelsRrenewable energiesEnergy conversion efficiencyother