Recent global events emphasize the importance of a reliable energy supply. One way to increase energy supply security is through decentralized off-grid renewable energy systems, for which a growing number of case studies are researched. This review gives a global overview of the levelized cost of electricity (LCOE) for these autonomous energy systems, which range from 0.03 $₂₀₂₁/kWh to over 1.00 $₂₀₂₁/kWh worldwide. The average LCOEs for 100% renewable energy systems have decreased by 9% annually between 2016 and 2021 from 0.54 $₂₀₂₁/kWh to 0.29 $₂₀₂₁/kWh, most likely due to cost reductions in renewable energy and storage technologies. This review identifies and discusses seven key reasons why LCOEs are frequently overestimated or underestimated in research, and how this can be prevented in the future. This overview can be employed to verify findings on off-grid systems, to assess where these systems might be deployed and how costs evolve.