Tidal energy converters: modelling and techno-economic assessment

The disjunction created by the limited and high cost of available land for onshore renewable energy project development and the increasing efficiency and competitiveness of marine renewable energies (MRE) has generated an accelerated shift in the energy transition to increase the installed capacity in the offshore marine zone. Techno-economic analysis plays a crucial role in supporting the competitiveness of the emerging marine energy sector against the traditional electricity pool. However, the limited experience of commercial MRE deployments and the scarcity of detailed cost data availability often lead to unrepresentative economic models. This paper aims to provide a cost model for different tidal energy converters (TEC) based on the bottom-up approach, and a power assessment based on the available tidal current models. Based on technical and economic data available in the literature, existing and new cost functions are proposed that consider a large number of components in the TEC field. Costs, performance, and competitiveness of three well-known TEC systems were estimated: monopile, floating, and gravity-based structures (GBS) in four European case studies: Fall of Warness (Scotland), Punta Pezzo (Italy), Fromveur and Raz Blanchard (France). Where available, tidal current data of accurate resource model is used, like DTOceanPlus dataset for France sites, otherwise the Operational Mercator forecast system is used and validated with measured data points. The bottom-up approach allowed observing that the nacelle and foundation are the elements generating the highest weight in the CapEx, and the predominant one varies depending on the location, while in the OpEx it is the spare part. In all sites, the highest values of average annual power and capacity factors were reached by the floating and monopile turbine, with maximum values in Fromveur equal to 395 kW and 39.47%, respectively, since they’re positioned closer to the sea level compared to GBS. The lowest CapEx and OpEx values were observed in Fall of Warness, followed by Fromveur, Razblanchard, and Punta Pezzo. At the first three sites, the monopile turbine generated lower costs than the floating and gravity-based structure associated with a lower need for materials given the shallow depths (50 m). However, at Punta Pezzo, floating has become the best technology with lower costs associated with a greater depth (100m). In all cases, an asymptotic decreasing trend in LCoE is observed as the installed capacity of the sites increases, with LCoE ranging between 230 and 50 €/MWh at 16 MW of installed power. Among all the sites analyzed, Fall of Warness and Punta Pezzo generated the lowest and highest LCoE values, respectively. The gravity-based structure turbine generated the highest LCoE associated with Punta Pezzo. Except of Punta Pezzo, in the rest of the sites, the monopile turbine generated the lowest LCoE values, followed by the floating type, with lowest LCOE in Fromveur. At Punta Pezzo, the floating TEC resulted in lower LCoE than the monopile due to water depth. This explains how water depth strongly affects the selection among the technologies, with best choice of monopile in shallow depths (<50 m) and floating at high depths.