Elsevier

Renewable Energy

Volume 34, Issue 3, March 2009, Pages 742-747
Renewable Energy

Life cycle assessment of a floating offshore wind turbine

https://doi.org/10.1016/j.renene.2008.04.004Get rights and content

Abstract

A development in wind energy technology towards higher nominal power of the wind turbines is related to the shift of the turbines to better wind conditions. After the shift from onshore to offshore areas, there has been an effort to move further from the sea coast to the deep water areas, which requires floating windmills. Such a concept brings additional environmental impact through higher material demand. To evaluate additional environmental burdens and to find out whether they can be rebalanced or even offset by better wind conditions, a prospective life cycle assessment (LCA) study of one floating concept has been performed and the results are presented in this paper. A comparison with existing LCA studies of conventional offshore wind power and electricity from a natural gas combined cycle is presented. The results indicate similar environmental impacts of electricity production using floating wind power plants as using non-floating offshore wind power plants. The most important stage in the life cycle of the wind power plants is the production of materials. Credits that are connected to recycling these materials at the end-of-life of the power plant are substantial.

Introduction

In this paper, we present a life cycle assessment (LCA) of electricity generation by an offshore floating wind power plant designed according to a concept of the Norwegian Sway Company. The floating wind power plant is not working yet, but Sway Company is in a final development of their concept. The results are compared with Ecoinvent database processes for electricity production in conventional offshore non-floating wind power plants and natural gas combined cycle power plants [1], [2].

There has been rapid growth in the use of wind power in recent years, in part because of its perceived importance for sustainable development. Wind power is a renewable energy source [3]. In contrast to gas and coal power plants, wind power plants convert wind energy into electricity without significant emissions or resource consumption during operation. Wind power technology has improved steadily and costs have declined [4]. The technological progress is apparent in the shift to higher nominal power of the wind turbines and in the movement to better wind conditions. Among the developments are larger turbines, higher towers, and the creation of offshore wind turbines. Some argue that the next step in wind power development is to shift into even deeper water offshore areas. This requires floating windmills. The advantages of floating windmills are improved wind conditions, reduced land disturbance, and access to a large resource. To float the windmill and make it withstand in rough offshore conditions, however, the design of the windmills must change and more materials are required for construction. Material production and the construction of the windmill are already the most emissions intensive steps in conventional windmills. It is, therefore, necessary to evaluate the environmental implications of the shift to deeper water.

In order to avoid shifting the environmental impact among different product life stages and to consider the trade-offs among different impacts, it is necessary to consider the whole life cycle of the product within its product system. LCA was developed to evaluate the environmental impact related to a product from material extraction and refining, manufacturing, transport and use phase to the disposal. It is a complex evaluation method, defined in Refs. [5], [6]. It facilitates the collection of data about inputs and outputs to and from the product system (inventory analysis) and the environmental performance of these inputs and outputs (impact assessment).

For an evaluation of any renewable energy system it is necessary to use a life cycle based approach because the operating costs and environmental impacts are nearly zero, but the required investments are substantial [7]. Several LCAs have been conducted for onshore and non-floating offshore wind power plants and other wind energy systems [8], [9], [10], [11], [12], [13]. These studies have documented that the life cycle impacts of wind power are substantially lower than the impacts of any fossil power plant, and that the energy input required to build a wind power plant is earned back in a few months. One would expect that these general conclusions also hold for a floating plant. There are, however, substantial differences between floating wind power plants and those mounted on the ground. Namely, more steel, and potentially concrete, are required for the construction of the floating structure, and installation and maintenance require the use of both ships, or rigs, and helicopters. This raises the question of how important the additional material requirements and the changed operating regime are in the overall life cycle. Will the increased power production due to stronger winds be able to offset these environmental disadvantages?

Section snippets

Life cycle assessment of a floating wind power plant

We present a process-based LCA of an offshore floating wind power plant according to the concept developed by Sway Company [14]. The product system is modeled using SimaPro [15], a software tool for LCA. Wherever possible we use relevant data based on information directly from producers. For generic inputs we use the Ecoinvent database [1].

CML 2 baseline 2000 V2.03 method was chosen for impact assessment [16]. Marine ecotoxicity impact category was excluded because it was found to give

Results – evaluation of the Sway concept floating power plant

The life cycle inventory of the aggregated unit process “Sway 5 MW floating wind power plant” is provided in Table 3 in Appendix I. This inventory is an intermediate step in the calculation of the LCI, as the input of Ecoinvent processes is required.

The impact assessment results are presented in Table 2.

We also present an analysis of the contribution of different processes to global warming, abiotic resource depletion and human toxicity. The largest contribution to global warming comes from the

Conclusion

Our preliminary life cycle assessment shows that the environmental impact of electricity production from a floating wind power plant does not significantly differ from electricity production in conventional offshore wind power plants if we assume a better capacity factor for the floating power plant. The only exception is the toxic emissions from material production. Marine ecotoxicity has not been investigated due to a lack of appropriate methods, and we have not collected data on direct

Acknowledgements

This work was partly financed by the EU project number CZ.04.3.07/4.2.01.1/0027 and Marie Curie Fellowship for the Life Cycle Assessment course within the Postgraduate School of Industrial Ecology (EU contract 029529). The most important data were provided by the Sway Company.

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