2015
Tenth International Conference on Ecological Vehicles and Renewable Energies (EVER)
Design and Performance Validation of a Hybrid Offshore Renewable Energy Platform A path to cost-efficient development of deepwater marine energy resources Dr. Jan Erik Hanssen, Dr. Lucia Margheritini
Pedro Mayorga
Reza Hezari
I-Tech SPRL, Brussels, Belgium
EnerOcean SL, Malaga, Spain
Inrigo AS, Trondheim, Norway
[email protected]
[email protected]
[email protected]
Dr. Keith O'Sullivan,
Israel Martinez, Ander Arriaga, Ivan Agos
Dr. J0fgen Hals Todalshaug
University College Cork, Ireland
Acciona Energia SA, Madrid, Spain
NTNU, Trondheim, Norway
o'sullivank0lbv.com
israel.martinez.barrios0lgmail.com
[email protected]
Dr. Jeff Steynor, Prof. David Ingram The University of Edinburgh, UK
[email protected]
Abstract-The paper presents the state of development of the W2Power hybrid, combining offshore wind and wave energy in a large but lightweight semi-submersible floating platform. Results of design optimisation and proof-of-concept experiments by tank testing are reviewed. Modelled hydrodynamic performance of the floating structure at full scale are compared with results of scaled validation tests in further tank experiments. Business cases for the hybrid are analysed using a simplified cost/revenue model, taking into account both CAPEX, OPEX and lifetime revenues from both wind- and wave-generated electricity.
Keywords-floating wind, hybrid, design, validation, CoE
I.
INTRODUCTION
Hybrid marine energy technologies combine the extraction of more than one form of energy in the ocean environment on a single installation [1]. Combining floating wind technology and wave energy may allow higher production of electric power for longer periods of time including at times when wind energy is unavailable. In many deep-water areas around the world, wind and wave resources are decoupled, so that the time window for producing electricity can be significantly extended by including also the wave energy [2].
offshore petroleum experience with semisubmersibles. In order to reach commercial viability, a wind & wave platform can and must be built much lighter than for oil & gas, which is feasible since no hydrocarbons will leak out in the event of accidents, and there are much less restrictive demands on the deck load: W2Power doesn't even have a deck. The W2Power hybrid incorporates numerous technological innovations and is patented. The platform is moored on partial sway, facing into the prevailing wind, preventing wind wake or shading between the twin turbines, allowing the pair to operate in tandem without a conventional yaw mechanism. The linear arrays of WEC's are attached to each side of the platform in a nearly symmetric fashion, allowing electricity production from incoming waves in a wide range of angles. The third buoyancy column houses the wave power take-off (PTO) subsystem, in essence a conventional hydro-power turbogenerator set driven by pressurised fluid from the WEC arrays. The geometry and construction of the wave absorbers have been through several deep design changes for increased efficiency and reliability. The W2Power platform is designed to take wind turbines of several OEM's and models in the power segment 3.0 - 4. 1 MW rated power. Depending on the wave energy resource, one unit (platform) can reach a rated power of 10 MW, or even higher.
However, it is challenging to design hybrids: Wave energy machines must be large to reach MW-scale power, while nearly all floating wind systems so far are designed to carry one wind turbine and thus do not offer much space. Furthermore, in order to make the system cost-efficient the wind turbine must be very large (>6 MW), heavy and (at least until recently) unproven.
Since its inception, the W2Power hybrid has completed a series of investigations for design optimization, performance improvement and validation. This paper describes, compares and summarizes some of the more significant results that have brought the technology to its current state of development.
W2Power was introduced as a concept by Pelagic Power in 2009 [3], at which time the company already had patented and sea-tested a free-floating (i.e., pelagic) wave energy converter (WEC) array. The basic idea of the hybrid was to combine this with using two commercially available offshore wind turbines, already proven at the time, supporting all the sub-systems on a triangular column-stabilised platform, which would draw upon
The first part will summarize the numerical investigations on the structure and present the current design of the platform. The second part reviews the laboratory setups and some results from tank testing of the platform in scale 1: 100 and the WECs in scale 1:30. The third section reports the results of the early business case analysis. Conclusions and further development steps will close the paper.
978-1-4673-6785-1115/$31.00 ©2015 IEEE
METHODOLOGY
II.
The methodology used for the design optimisation of the W2Power system is an iterative procedure that combines lab oratory tests and numerical simulations. Several rounds of tank testing have been completed and results compared with design and numerical modelling, to arrive at a workable design that is compatible with the needs of the hybrid technology, safety and ease of installation, and capable of being fabricated in series at yards I sites that can handle structures of up to 80 m beam. The purpose of the work summarised here was to assess the feasibility and economic application potential of the W2Power system, especially with regard to hydrodynamic performance, energy production and cost-efficiency. Optimizing the platform design in terms of costs is in this case directly proportional to reducing the weight of construction steel needed. III. A.
B.
Survivability analysis
Survivability analysis consisting in 1 hour simulations with all the loads aligned in the same direction has been performed numerically for three real sea locations of possible interest. The characteristics of these locations are summarized in Table 1 of the contour condition, and for 1 mls of current speed. Results are presented in Table 2. 1:
TABLE
CHARACTERISTICS OF THE THREE LOCAnONS
FOR THE SURVIVABILITY ANALYSIS. Location 3, 200m
Location 14, 100m
Location 14, 200m
Hs(m)
Tp(s)
V wind 10m
Hs(m)
Tp(s)
V wind 10m
Hs(m)
Tp(s)
V wind 10m
8.797
14.839
27 .9 48
13.508
15 . Q2 5
33.307
13.508
15.025
33.307
11. 23
15.871
26
15.234
15.565
32
15.234
15.565
32
11.408
15.333
24.S
15.09
15.735
30
15.09
15.735
30
11.5
15 . 7
24.3
14.572
15.59
28
14.572
15.59
28
11.222
15.619
21.5
15.3
15.5
31.4
15.3
15.5
31.4
- mls
- mis
- mls
NUMERICAL DESIGN
Design improvements
The W2Power platform has been the object of numerical investigations using Genie and HydroD (from DnV's SESAM package) for structural and preliminary hydrodynamic analysis and SIMO for detailed hydrodynamic TD simulations. The originally sketched platform had natural frequencies of heave and pitch that would need heavy, costly constructions for safety at sea. Hence, a 4-stage design revision programme was undertaken to optimise the hydrodynamics for ocean areas of possible application, limiting fatigue loads, and reduce the steel mass required. Space here allows only a summary of the work. Design cases were screened by spreadsheet-based tools and promising ones analysed in the frequency domain by WADAM - calculating the Response Amplitude Operators (RAO's) of motion and forces. This was followed by analysis in the time domain by SIMO, and fatigue analysis by SIMO-R1FLEX. The result was a platform showing natural heave periods of more than 20 sec. and pitch periods over 30 sec. An optimised mooring system allows adequate station-keeping for the wind vaning platform and modified braces allow greater stiffness of the structure and reducing the steel weight by >25%.
Figure l. Summary of the evolution of the platform design: version 1 in black, version 2 in yellow and version 3 in red.
TABLE
2: RESULTS OF NUMERICAL SIMULAnON TABLE3.
OF THE THREE DIFFERENT LOCAnONS IN Site condition Platform motions
Max. pitch motion (deg) Max. nacelle acceleration 1m/52) Tension in the mostly-loaded
Max. tension at the fairlead (kN) Safety factor mooring lines WT tower response
Max. bending moment at the tower
I I 1 1 I �
I
Site No.3, 200m
I
Site No. 14, 100m
1 1
Site No. 14, 200m
1 1
8.6
13.91
14.0
2. 39
3.30
3.30
1 1
1 1
2941
9731
4680
2.2
2.1
1.9
359839
1
494123
1
482491
loads in the connection between the platform and the WECs (for this concept, loads in operation in th PTO)
Max. contact force {kNm}
C
I
12116
1
119
