A review of conventional and exergetic life cycle assessments of organic Rankine cycle plants exploiting various low-temperature energy resources

The importance of organic Rankine cycle (ORC) plants to the development of future energy infrastructure is widely acknowledged, due largely to their ability to exploit low-temperature thermal energy sources such as industrial waste heat and renewable energy resources. In this regard, different schemes are being proposed in the literature for the technical and economic developments of ORC plants. Also, the environmental feasibility assessments of ORC-based energy systems have been gaining gradual attention recently, but relative to the technical and economic aspects, the life cycle assessment (LCA) studies on ORC are at an infancy stage. It is therefore aimed in this study to systematically review and collate in a single document, the conventional and exergy-based life cycle assessment studies applied to ORC plants. Doing so, it was found that less than 3% of the over 7000 documents available on ORC in the SCOPUS database analyzed the environmental impact. Also, the ecoinvent was observed as the LCA inventory database most frequently in use, usually in the SimaPro software. Additionally, literature data revealed that the choice of the organic working fluid and the consideration of its leakage over the plant's lifetime have significant effects on the environmental impacts of ORC plants. Moreover, the common methods of conducting the exergy-based LCA (exergoenvironmental analysis) of ORC plants are succinctly reported in this manuscript, including the definitions of the most relevant exergoenvironmental performance metrics. It is hoped that this effort would spur the inclusion of LCA in future analyses of ORC plants, towards the achievement of a more sustainable energy conversion technology.