Ecohydrology Students’ Scientific Association of University of Tehran Water,Soil and Air Protection 2 1 2021 04 21 A Review on Hybrid Renewable Energy Systems (Hydro, Wind and Solar) and Related Novel Studies, Focusing on Power Generation Worldwide A Review on Hybrid Renewable Energy Systems (Hydro, Wind and Solar) and Related Novel Studies, Focusing on Power Generation Worldwide 57 69 80934 FA Shaghayegh Danehkar M.S. in Ecohydrology, Department of Renewable Energies and Environment, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran Hossein Yousefi Associate Professor, Department of Renewable Energies and Environment, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran Journal Article 2021 04 09 Considering the fast growing demand for electricity, increasing costs of power generation by fossil fuels and simultaneously cost-effectiveness of hydropower, solar and wind sources in electricity production, the importance of replacing conventional and high carbon sources with clean energies is increasing by day. Nevertheless, the development of renewable energy systems has its own challenges; the intermittent and unpredictable nature of wind and solar sources made it impossible to fully relay on single source renewable energy systems for power generation in many parts of the world. Thus, in the last two decades hybrid systems consisting of two or more renewable sources are drawing attention from experts and researchers as a suitable solution, due to their role in increasing production stability of the system and decreasing related costs. In the present study first, the situation of electricity production around the world based on source and country, and current costs of power generation from fossil fuels in comparison to renewable sources are briefly evaluated. Then hybrid energy systems consisting of the three main renewable sources (hydro, solar and wind) with the goal of supplying electricity worldwide are reviewed and novel finding and designs of related studies in regard of optimization and feasibility of such systems are mentioned. Considering the fast growing demand for electricity, increasing costs of power generation by fossil fuels and simultaneously cost-effectiveness of hydropower, solar and wind sources in electricity production, the importance of replacing conventional and high carbon sources with clean energies is increasing by day. Nevertheless, the development of renewable energy systems has its own challenges; the intermittent and unpredictable nature of wind and solar sources made it impossible to fully relay on single source renewable energy systems for power generation in many parts of the world. Thus, in the last two decades hybrid systems consisting of two or more renewable sources are drawing attention from experts and researchers as a suitable solution, due to their role in increasing production stability of the system and decreasing related costs. In the present study first, the situation of electricity production around the world based on source and country, and current costs of power generation from fossil fuels in comparison to renewable sources are briefly evaluated. Then hybrid energy systems consisting of the three main renewable sources (hydro, solar and wind) with the goal of supplying electricity worldwide are reviewed and novel finding and designs of related studies in regard of optimization and feasibility of such systems are mentioned. https://wsapsj.ut.ac.ir/article_80934_281c0bc1569bdd89f62d94952d24a3fd.pdf