Windcrete concept scalability: from 2MW to commercial stage
Pau Trubat, Alexis Campos, Daniel Alarcón, Climent Molins
Universitat Politècnica de Catalunya - BarcelonaTech, Catalunya, Spain
The design of a new solution from the early stages to the fully commercial units needs to achieve and overtake the different technology readiness levels (TRL). The floating platforms for offshore wind turbines (FOWTS) are not an exception. Moreover, there are some handicaps for these technology solutions like the high initial investment costs, the low number of available offshore wind turbines for full scale prototypes, or the big differences of the construction and installation between the initial smaller prototypes and the final designs in a commercial stage.
Windcete is a monolithic concrete spar platform, including both the tower and the floater in a unique concrete member of which a proof of concept was developed in the KIC Innoenergy AFOSP project. The monolithic characteristic means that joints are avoided, thus the fatigue resistance is increased since weak points are driven out. The whole structure is in compression state by the use of active reinforcement, and it is designed to avoid traction at any point during the span life of the platform. Furthermore, the use of concrete allows to reduce the Capital Expenditure (CAPEX) because its low cost, and also reduces the Operational Expenditure (OPEX) due to the its high resistance against the marine environment.
This article highlights the scalability of the concept through the main dimensions, construction and installation processes for three different Windcrete units. These units are predesigned for different TRL to compare the evolution from an initial prototype to commercial units for a wind farm.
Three different stages of the progress towards the commercialization, corresponding to increasing TRLs, are chosen to represent the evolution of the final designs of a FOWT. First, a prototype for a 2MW FOWT in a relevant marine environment as TRL6. Second, five units of 6 MW FOWT in a relevant marine environment as a pre-commercial stage for a TRL 7-8. Finally, thirty units of 8 MW and fifty units of 10 MW FOWT in first and mature commercial offshore wind farm stage respectively. For every stage, the main dimensions and costs of each platform are assessed. Also the proposed construction and installation methods for each stage are described, including the estimated construction types, the required infrastructure and the equipment and the vessels.
For all the stages, the dimensions, materials and construction costs, and the installation of each platform costs will be assessed.
The construction costs are evaluated taking account the number of devices that are considered in each stage. The main factors considered are the cost of the materials (concrete, and steel), the frameworks, the workers and the time. The construction can be done in existing dry docks or in a harbour with the heavy lifting operations.
The installation process is defined for each stage taking account the size and number of units. The time needed for each marine operation is estimated, and the vessels used, common and specific purpose ones, are described. Also some estimates of the LCOE achievable will be included in the paper.
The paper clearly demonstrates the very good scalability of floating offshore wind turbines in the particular case of Windcrete concept. As it is well known, the pace of the increment of the mass (and costs) of the floating units is less than linear with the power of the turbine, even that for a unique prototype the costs can be higher. This favours the use of the most powerful existing turbines.
The paper shows the main properties of Windcrete concept, from prototype to the commercial units. These properties such as the main sizes and the amount of material needed, can be an indicator of how new infrastructures should be designed, and new construction and installation solutions can be created. The advantages of scalability for the Implementation of floating wind technology worldwide is a key factor, and this paper gives details how can be applied in FOWT's in particular in Windcrete concept.
Also main drivers of LCOE for Windcrete are presented that can be used in other studies for comparing several FOWT solutions.