Session: 09-03-01 Current and Tidal Energy - 1

Paper Number: 78417

78417 - The Relationship Between Reliability and Environmental Impact in Tidal Stream Turbine Deployments 

With greenhouse gas emissions of the order of 30gCO2e/kWh, tidal stream energy has the potential to provide electricity supply with vastly lower environmental impact than fossil-fuel generation, while simultaneously avoiding the intermittency problem common in other types of renewable energy generation. However, cost of tidal stream energy is currently high and the sector has suffered from investor reluctance. O&M costs can be significant and perceived reliability challenges have limited the growth of the sector to date. Questions around the overall environmental impact of tidal stream energy are also to be addressed, including (in common with the wind energy sector) around the disposal of turbine blades.

Though a plethora of designs exist for the capture of tidal stream energy, horizontal-axis devices on either fixed or floating moored platforms are arguably the only types to have been deployed to a quasi-commercial level. In this work we study the reliability, operation and maintenance characteristics, and total environmental impact of these two forms of tidal stream energy turbine.

Reliability was studied through a comprehensive assessment of all global tidal stream energy deployments to date. All deployments were classified by device type, size, number of turbines, and a series of site characteristics such as mean and peak flow rate. The resulting database is now maintained as a resource for the sector.

Full lifetime environmental impact of fixed and floating deployments were quantified using Life Cycle Assessment (LCA), based on data provided by leading device developers. Sensitivity assessment was used to quantify uncertainty in some areas and ensure fair comparison between cases.

The surface-piercing nature of floating devices offers maintenance advantages over submerged seabed devices due to easier access and reduced downtime, but these devices are statistically more likely to experience minor failures and curtailments. The two device types yield similar environmental impacts in many aspects, but in others there is significant variation, particularly related to material use and maintenance requirements. Reliability is found to be a key factor in further reducing the environmental impact of the sector, and in the reduction of the cost of energy.

This work summarises the current position of the sector in terms of reliability and learning rate, and the relationship between this and environmental impact. Historical and recent data is used and projections of future trends are presented.

Presenting Author: Stuart Walker University of Exeter

Authors:

Stuart Walker University of Exeter
Philipp Thies University of Exeter
Lars Johanning University of Exeter