Cost modelling of Offshore Wind Energy in Northern Europe

Abstract of Phd Thesis

Tim Cockerill

Locating large wind farms offshore avoids many of the social and environmental conflicts that limit development on land. The major disadvantage is that the costs associated with offshore construction tend to make any energy produced more expensive than that from comparably sized onshore farms. In view of the marginal economics of even the most competitive wind farms, there is a need to identify economically efficient configurations for offshore farms. This requires an understanding of the parameters that drive both the cost and the design of offshore farms, together with knowledge of the relationships between them.

This thesis develops a cost modelling methodology for the analysis of bottom mounted offshore wind farms located in northern European waters. The

approach attempts to replicate in simplified form elements of the design process for an offshore farm. Starting with environmental and overall engineering parameters, the methodology `sizes' the components required for a farm, estimates their cost and energy production performance, and hence predicts the cost of energy.

While all major farm components are considered, the focus of the work described here is on structural aspects. This is because the support structure is directly influenced by local environmental conditions and must be custom designed for each location. Only bottom-mounted structures are examined in this thesis, and analysis is further constrained to mono-tower designs with piled or gravity-type foundations.

The cost modelling methodology is implemented as a computer code and used for a series of parameter studies. The sensitivity of the cost of energy from offshore farms to changes in environmental and overall engineering parameters is investigated. The studies suggested that the wind resource should be the main driver in site selection for good economics.

During the design of an offshore wind farm, the various overall engineering parameters can in principle be chosen independently. In contrast, environmental parameters are linked through geography. While locations can be chosen arbitrarily, environmental parameters do not vary independently in practice. Good wind conditions for example, may be found far offshore.To allow a realistic investigation of the impact of location and combinations of environmental parameters on farm economics, a Geographic Information System (GIS) of offshore conditions has been coupled with the model. Further parameter studies using the GIS demonstrated that environmental parameters other than the wind resource must be accounted for in the process of selecting a site with good economics.