Sustainable Generator Design for Offshore Wave Energy Converters: A Case Study

Offshore wave energy offers significant potential for low-carbon electricity generation, but the sustainability and economic viability of wave energy converters (WECs) depend strongly on the design of their power-take-off systems. This paper investigates sustainable direct-drive generator solutions for the Mocean Energy Blue-X offshore hinged-attenuator WEC. Several low-speed, high-torque permanent-magnet generator topologies were evaluated, including surface-mounted permanent-magnet synchronous machines (SPMSMs) and modular spoke-PMSMs employing different combinations of neodymium-iron-boron (NdFeB) or ferrite magnets with copper or aluminum conductors. A multi-objective optimization framework was developed to minimize the generator-related cost and cogging torque, subject to electromagnetic, thermal, mechanical, and efficiency constraints. System-level cost of energy (CoE) is evaluated through sensitivity analysis of the generator-related share of total WEC capital cost. Cradle-to-gate embodied carbon associated primarily with material production is also evaluated. Results show that copper-wound designs generally provide more favorable CoE. Among these, the spoke-PMSM employing ferrite magnets shows the strongest tendency towards the lowest CoE, whereas the NdFeB spoke-PMSM achieves the lowest embodied carbon. Within the adopted cradle-to-gate boundary, structural components dominate embodied emissions, contributing approximately 60–70% of the total. The results highlight that material-level advantages do not necessarily translate into machine-level benefits because of their effects on efficiency, machine size, and structural requirements.