A comparative life cycle assessment of marine power systems

Despite growing interest in advanced marine power systems, knowledge gaps existed as it was uncertain which configuration would be more environmentally friendly. Using a conventional system as a reference, the comparative life cycle assessment (LCA) study aimed to compare and verify the environmental benefits of advanced marine power systems i.e. retrofit and new-build systems which incorporated emerging technologies. To estimate the environmental impact attributable to each system, a bottom-up integrated system approach was applied, i.e. LCA models were developed for individual components using GaBi, optimised operational profiles and input data standardised from various sources. The LCA models were assessed using CML2001, ILCD and Eco-Indicator99 methodologies. The estimates for the advanced systems were compared to those of the reference system. The inventory analysis results showed that both retrofit and new-build systems consumed less fuels (8.28% and 29.7% respectively) and released less emissions (5.2-16.6% and 29.7-55.5% respectively) during operation whilst more resources were consumed during manufacture, dismantling and the end of life. For 14 impact categories relevant to global warming, acidification, eutrophication, photochemical ozone creation and PM/respiratory inorganic health issues, reduction in LCIA results was achieved by retrofit (2.7-6.6%) and new-build systems (35.7-50.7%). The LCIA results of the retrofit system increased in ecotoxicity (1-8%), resource depletion (1-2%) and fossil fuel depletion (17.7-161.9%). Larger magnitude of increase was shown by the new-build system in ecotoxicity (90-93.9%) and fossil fuel depletion (391.3%) as a result of handling additional scrap. Relative contribution of significant components towards environmental impact remained profound for the retrofit system (i.e. more than 84% for all impact categories) and became more prominent for the new-build system (approximately 99% for 18 impacts). For retrofit and new-build systems respectively, changes in fuel consumption quantity by ±10% and ±20% varied (i) ecotoxicity and land use by no means, (ii) fossil fuel depletion by 0.95-1.50 and 4.81-5.01 times assessed by CML2001 (or 0.95-1.50 and 5.12-5.32 times assessed by Eco-Indicator99); and (iii) the remaining impact categories by 0.65-1.37 and 0.34-0.92 times. The new-build system showed the greatest mitigation potential in 18 impact categories. The retrofit system was more environmentally friendly than the reference system. Appropriate life cycle management was warrant to avoid burden shifting whilst alleviating the environmental burdens at the same time.