The world's first commercial-scale grid-connected tidal current energy installation will feature the Seagen marine current turbine developed by Marine Current Turbines Ltd. With potential for the manufacture of significant numbers of such devices there is a need to assess their environmental impact and, in particular, their life cycle energy and carbon dioxide (CO 2 ) performance. This paper presents an analysis of the life cycle energy use and CO 2 emissions associated with the first generation of Seagen turbines. The detailed assessment covers the embodied energy and CO 2 in the materials and manufacturing of components, device installation, and operation along with those for decommissioning. With relatively conservative assumptions, and despite the early stage of development, the study shows that at 214 kJ/kWh and 15 g CO 2 /kWh, the respective energy and carbon intensities are comparable with large wind turbines and very low relative to the 400 to 1000 g CO 2 /kWh typical of fossil-fuelled generation. The energy payback period is approximately 14 months and the CO 2 payback is around 8 months. The embodied energy and carbon show limited sensitivity to assumptions with environmental performance remains excellent even under the most adverse scenarios considered. Materials use is identified as the primary contributors to embodied energy and carbon with shipping also significant. Improvements in the environmental impact of the Seagen can be achieved primarily by increased structural efficiency and the use of alternative installation methods to increase recovery of steel at decommissioning.

The world's first commercial wave farm will feature the 'Pelamis' wave energy converter developed by Ocean Power Delivery. With potential for the manufacture of significant numbers of such devices there is a need to assess their environmental impact and, in particular, their life cycle energy and carbon dioxide (CO 2) performance. This paper presents an analysis of the life cycle energy use and CO 2 emissions associated with the first generation of Pelamis converters. With relatively conservative assumptions, the study shows that at 293 kJ/kWh and 22.8 gCO 2 /kWh the respective energy and carbon intensities are comparable with large wind turbines and very low relative to fossil-fuelled generation. The energy payback period is approximately 20 months and the CO 2 payback is around 13 months. Material use is identified as the primary contributor to the embodied energy and carbon with shipping (including maintenance) accounting for 42%. Improving the Pelamis' environmental performance could be achieved by increasing structural efficiency, partial replacement of the steel structure with alternative materials, particularly concrete, and the use of fuel-efficient shipping.

7This article explores an automated approach for the efficient placement of substations and 8 the design of an inter-array electrical collection network for an offshore wind farm through 9 the minimization of the cost. To accomplish this, the problem is represented as a number 10 of sub-problems that are solved in series using a combination of heuristic algorithms. The 11 overall problem is first solved by clustering the turbines to generate valid substation positions. 12From this, a navigational mesh pathifinding algorithm based on Delaunay triangulation is 13 applied to identify valid cable paths, which are then used in a mixed-inter linear programming 14 problem to solve for a constrained capacitated minimum spanning tree considering all realistic 15 constraints. The final tree that is produced represents the solution to the inter-array cable 16 results. This method is applied to a planned wind farm to illustrate the suitability of the 17 approach and the resulting layout that is generated.

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Purpose To date, very few studies have attempted to quantify the environmental impacts of a wave energy converter, and almost all of these focus solely on the potential climate change impacts and embodied energy. This paper presents a full life cycle assessment (LCA) of the first-generation Pelamis wave energy converter, aiming to contribute to the body of published studies and examine any potential trade-offs or co-benefits across a broad range of environmental impacts. Methods The process-based attributional LCA was carried out on the full cradle-to-grave life cycle of the Pelamis P1 wave energy converter, including the device, its moorings and sub-sea connecting cable up to the point of connection with the grid. The case study was for a typical wave farm located off the north-west coast of Scotland. Foreground data was mostly sourced from the manufacturer. Background inventory data was mostly sourced from the ecoinvent database (v3.3), and the ReCiPe and CED impact assessment methods were applied. Results and discussion The Pelamis was found to have significantly lower environmental impacts than conventional fossil generation in 6 impact categories, but performed worse than most other types of generation in 8 of the remaining 13 categories studied. The greatest impacts were from steel manufacture and sea vessel operations. The device performs quite well in the two most frequently assessed impacts for renewable energy converters: climate change and cumulative energy demand. The carbon payback period is estimated to be around 24 months (depending on the emissions intensity of the displaced generation mix), and the energy return on investment is 7.5. The contrast between this and the poor performance in other impact categories demonstrates the limitations of focussing only on carbon and energy. Conclusions The Pelamis was found to generally have relatively high environmental impacts across many impact categories when compared to other types of power generation; however, these are mostly attributable to the current reliance on fossil fuels in the global economy and the early development stage of the technology. Opportunities to reduce this also lie in reducing requirements for steel in the device structure, and decreasing the requirements for sea vessel operations during installation, maintenance and decommissioning. Electronic supplementary material The online version of this article (10.1007/s11367-018-1504-2) contains supplementary material, which is available to authorized users.