Review of Life Cycle Assessments of Geothermal Heating Systems

The State of Geneva in Switzerland is determined to increase the share of renewable energy in its heating and cooling mix. Geothermal energy from shallow and medium depths (up to 3000 m) is identified as one of the key renewable sources. As compared to other renewable energy sources, there are relatively few studies on the environmental impacts of geothermal energy. This paper provides a systematic review of 28 geothermal heating and cooling system designs from 25 Life Cycle Analysis (LCA) publications. This review discusses (1) the scope of the existing LCA studies; (2) technologies assessed; (3) methodologies and reported environmental impacts; (4) different factors that give rise to the uncertainty and variability of the result; (5) limitations and challenges faced during the studies; and (6) gaps in the literature and future research needs. The findings show that the systems with borehole heat exchangers and heat pumps were analyzed the most. These geothermal systems did not necessarily perform better environmentally than oil boilers. Sensitivity analyses showed that electricity mix and coefficient of performance of the heat pumps were the key influencing factors. Studies on geothermal systems involving groundwater extraction at shallow and medium depths were rarely carried out despite their wide deployment in Europe. In the few existing studies, such systems had better environmental performance than smallscale oil boilers. Additionally, in general, uncertainty and variability were not analyzed.