Comparison of floating offshore wind turbines with floating solar PV in central Mediterranean waters

Abstract

Malta, being a very small and densely populated island in the central Mediterranean, has limited land space and the territorial waters are mostly too deep for conventional offshore wind farms to be constructed. This paper presents a preliminary engineering analysis to develop two cost-optimized structures to support (1) a multi-megawatt scale wind turbine and (2) a solar photovoltaic farm with the same energy production as that of the single wind turbine. The primary objective of this work is to determine the most economically feasible option for harvesting renewable energy at sea: offshore wind or offshore solar photovoltaic energy. Reviewing the available technologies enabled the selection of the most appropriate conceptual design for each of the energy generation platforms using basic engineering theory. Calculations were carried out on the general arrangement and overall hull design taking into consideration wind and wave loading, weight, buoyancy and stability, static analysis, mooring arrangement and cost. The support structure has been proposed according to the guidelines given by offshore wind turbine standards and reflects typical local climatic conditions in the centre of the Mediterranean Sea. Load calculation were undertaken at wind speeds of 25 ms-1 and at 42.5 ms-1, which imply operational and extreme wind conditions, respectively. Hydrodynamic loads under extreme wave conditions were also modelled. The calculations were carried out through a simple iterative model which was set up using the solver algorithms of Microsoft Excel. STAAD Pro ver8i software was used to undertake static analysis simulations and determine deflections, compressive, tensile and shearing forces and bending moments. The final part of the analysis consisted of formulating a cost model for each of the two platform types and estimating the levelised cost of energy (LCOE) for both floating wind and solar PV in the deep offshore environment.