One of the key developments of the marine energy industry in the UK is the demonstration of near commercial scale devices in real sea conditions and the collection of performance and environmental data to inform permitting and licensing processes.The ETI’s ReDAPT (Reliable Data Acquisition Platform for Tidal) project saw an innovative 1MW buoyant tidal generator installed at the European Marine Energy Centre (EMEC) in Orkney in January 2013.The project demonstrated the performance of the tidal generator in different operational conditions, aiming to increase public and industry confidence in tidal turbine technologies by providing a wide range of environmental impact and performance information, as well as demonstrating a new, reliable turbine designThis report defines a methodology to calculate the CO2 payback interval for a tidal stream generator, in terms of the embodied life-cycle Greenhouse Gas (GHG) emissions arising and displaced by the full life cycle of the generator.The report considers the CO2 payback calculations at both the turbine and array levels. It coversRequirementsLife Cycle Assessment (LCA) System DefinitionsLife Cycle Impact (LCI) AssessmentLife Cycle ProcessesTechnology Level RationaleTidal Stream Array Siting ConsiderationsSpecific Modelling ConsiderationsCalculation of Carbon Payback IntervalEvaluation and Reviewing of ResultsReporting and Interpretation of ResultsAppendicesA: System Boundary DetailsB: Waste DisposalC: Transport DetailsD: Tidal Current Probability DataE: Data Collection ConsiderationsF: GLobal Warming Potential