The relationship between reliability and environmental impact in tidal stream turbine deployments

Though tidal stream energy is a source of electricity with low environmental impact, the manufacture and operation of tidal energy devices has inbuilt environmental impact and cost. Maintenance costs can be significant and reliability challenges have limited the growth of the sector to date. This study considers two designs of tidal stream energy device (seabed-fixed and floating horizontal axis turbines) and estimates the environmental impact of maintenance in the context of sector reliability to date. Lifetime environmental impact of fixed and floating devices were quantified using Life Cycle Assessment methods, based on reliability data for 58 deployments. Maintenance has a significant impact on the total environmental impact of tidal stream energy devices, contributing between 4% and 25% of total embodied emissions. Floating devices offer maintenance advantages over seabed-fixed devices due to easier access and reduced downtime, but these devices are more likely to experience minor failures and curtailments. The results show that standard maintenance contributes more to the overall environmental impact than the mitigation of failure or curtailment, due to frequency and the need for replacement parts. Type and manufacture of parts were found to be a major contributor to environmental impact, making up 97% of the impact of standard maintenance for floating devices and 91% for seabed-fixed devices. Reducing the frequency of part replacement was found to be the best route to reducing the environmental impact of maintenance.