Transportation contractors, Mar Train, completed a trial lift of the Subhub recently to reduced the risks associated with the load out to the quayside at Harland & Wolffe, Belfast, Northern Ireland.
The weight of Subhub throughout the build has been controlled in order to achieve the load out requirements which were proven by the Mar Train test lift.
As a result QED have refreshed all their stability models to ensure compliance with each load condition i.e. load out, transit to site, installation and recovery, and in-service conditions. Damage conditions and reserve buoyancy have also be considered carefully.
Exit is planned early in the new year, shortly after, the Subhub will be launched for final ballast testing and then towed to site ready for installation.
This load out phase of the project demonstrate how a tidal power plant such as Subhub (210kW) can be fully integrated at the quayside and deployed, installed and recovered in a single, quick offshore operation. There are no other moorings to lay just a single dry mate connection to make to an export cable which is grid compatible.
QED Naval have completed the commissioning of all onboard ballast and instrumentation systems ready for testing and launch early in 2018. This community version is a big step to proving the claims about competing with offshore wind for CFDs at utility scale.
QED Naval is working with Schottel Hydro on this 190kW version which is competitive, in terms of LCOE, with diesel generation for island communities’ or offshore power generation for aquaculture offering excellent niche market opportunities recently forecast by Aquatera.
However, Subhub was always designed for utility scale projects, removing the requirement for large specialist vessels at expensive day rates and multiple marine operations offshore. Where Subhub requires only a single offshore operation using smaller vessels and/or barge at low day rates.
Fundamentally, the concept of Subhub using buoyancy and good submerged stability to install the turbines scales very well. Also, the ballast ratios, for the required on-bottom weight to secure the turbines on the seabed, scales in their favor. The utility version is more slender and uses simpler construction methods reducing fabrication costs still further enabling the acceleration effects of the semi-duct to be applied to every turbine. QED’s latest CFD models when combined with a tidal harmonic models for the site and power curve of the tidal turbine show increases in yield of up to 50% year on year when compared with typical monopile structures. Subhub effectively increases the capacity factors of the site.
An independent report by a Master Mariner has stated that installation and recovery costs of a utility scale Subhub can be reduced by 50 to 90% compared with current methods. The seaworthy design, stability when submerged and the control of the ballasting process make the Subhub less sensitive to wave loading during installation. This allows it to be installed and recovered over broad weather windows and hence the availability for maintenance is higher. This attributes a large reduction in maintenance costs.
QED Naval pride themselves on the understanding of the combined effects of wave and tidal loading learning huge amounts from their tank testing at Flowave, open water testing at The Underwater Centre in Loch Linnhe. Their collaborations with EMEC/FORESEA, and QUB as part of the Tidal Turbine Turbulence (TTT3) project have provided unrestricted access to real measured tidal data using ADCP systems for accurate tidal modelling and turbulence measurements. QED’s work on turbulence modelling in collaboration with the National Oceanographic Centre (NOC) is thought to be class leading and provides more assertive results for energy yield calculations.
All this learning has been combined into Monte Carlo simulations for various projects QED have assessed which provides a sound basis to presenting the LCOE figures and making project finance decisions.
All these claims will be assessed in the next stage of testing to be commenced early 2018.
QED Naval are pleased to annouce the acceptance of the Subhub – Kraken’s main hull fabrication including all outfit hotwork.
An important part of the acceptance was the main hull lift off the cradle and supporting structure onto the Subhub’s main leg structure to fully support her ample weight.
Factory Acceptance Tests (FATs) which pressurised each of the ballast tanks were completed successfully along with all the load testing of the lifting equipment including the main hull lifting lugs (68t load) and the modular solid ballast blocks (2 off) each weighing 20t.
All the welding plans and Non-Destructive Tests (NDTs) have been completed and approved.
QED Naval would like to take the opportunity to thank their prime contractors, Cimpina, in their support and commitment that they have provided to get the project to this point of completion.
QED Naval have now taken responsibility for all the outfitting of the Subhub and has completed all the internal outfit. Kraken is now awaiting painting which will be completed in early October.
QED Naval are currently commissioning and testing all the ballast and instrumentation systems prior to a planned launch in early 2018.
QED Naval and their selected fabricators, Cimpina based in Northern Ireland, are soon to complete the Subhub community demonstrator ready for deployment to EMEC in the next couple of months. Once at EMEC it is intended to use the FORESEA funding to conduct a phased set of sea trials to demonstrate that a tidal array can be installed and recovered in a single offshore operation using small vessel with low date rates.
Phase 1a installation and recovery trials at the scale tidal test site using replica turbines and equipment allowing marine operators to gain valuable experience of installation method.
Phase 1b aims to integrate Schottel Hydro SIT-250 turbines providing Subhub with a capacity of 190kW, capable of powering 50 homes. This collaboration includes SME who will be providing their ‘Flipper’ support structure for bi-directional flow, Platform Operation Module (POM), for controlling the platform at EMEC and Subsea Transformer Module (STM) to transmit the grid friendly power ashore.
Phase 2a will then move operations over to the Falls of Warness site. The aim is to demonstrate the installation and recovery over a wide spectrum of tidal flow and wave heights since the deployment method uses Subhub’s unique submersible stability characteristics that are less sensitive to extreme conditions.
Phase 2b will demonstrate the long term deployment capabilities, operational stability of its gravity based anchoring system and increased performance characteristics of the turbines which have shown insensitivity to cross flows in tank testing at Flowave. An O&M strategy will be developed for its customers assessing fatigue loads, marine growth and corrosion factors.
Phase 3 will be used to assess the environmental impacts of a longer term deployment and demonstrate the ability of the Subhub to be quickly and easily decommissioned from the site.
Once this testing is complete it is intended to offer the Subhub for sale and re-use it at another site. All going well Subhub will be further developed utilising a test berth at EMEC with a larger capcity machine rated at 1.2MW. QED Naval is in early stage discussions with several collaborative partners who would like to be involved in this larger scale development due to be deployed in 2018.
Cimpina based in Northern Ireland in Belfast Docks have been awarded the build contract for the Subhub. They were among 6 different fabricators contending for the business.
Work commenced in November and the outer shell was taking shape before Christmas. Completion is expected in the first quarter of next year.
The Community Subhub with a capacity of 200kW using Schottel tidal turbines will be launched and transported up to EMEC where long term testing will be conducted, as part of the FORESEA project, to demonstrate the Subhub’s capabilities with installation and retrieval. The performance of the Subhub and turbines will be monitored. Long term operations and maintenance strategy will be developed to validate the OPEX cost model and hence the LCOE for a Subhub related project.
QED Naval are excited to announce that they have been awarded funding for the open sea testing at the EMEC tidal test sites. This provides access to both the scale tidal test site along with the grid connected Falls of Warness site.
QED Naval have engaged in pre-commercial discussions for a contract at EMEC to carry marine operations at their test site that aims to validate claims of the Subhub tidal platform. These include:
Reduction in the cost of deployment of tidal turbines using a single marine operation to install the turbines ready for operation on the seabed within a broad range and tidal states and wave conditions.
Enhanced power output and site capacity factors.
Retrieval of the system for maintenance in a single marine operation using a low cost multicat vessel over a broad range of conditions.
Significant site feasibility work has already been carried out by QED Naval as part of the FORESEA application which will ultimately see them connect tidal turbines to the grid for verification of the enhanced performance characteristics provided by the Subhub foundation solution.
GIS mapping tool containing all the flow data, berth positions and bathymetry of the Falls of Warness tidal test site.
QED Naval are pleased to welcome Thomas Nevalainen to the team. Thomas joins QED Naval from Strathclyde University where he is about to complete his Ph.D. His thesis entitled “The effect of unsteady sea conditions on tidal stream turbine loads and durability” allows QED Naval to extend its wave and tidal loading capabilities and add BEMT methods to calculating turbine loads as part of a more streamlined optimisation process for QED’s Subhub foundation structure. CFD methods can then be used to assess the finalised design.
Thomas will take over the management of access to the Hartree supercomputer which is used to improve turnaround times on large models and increase the speed of learning from weeks to days. QED Naval have access to ANSYS Fluent and X-Flow on the Hartree supercomputer. Fluent is a sophisticated CFD package that provides access to a large number of turbulence models and mesh developments such as polyhedral meshes that streamline the size of the model and improve accuracy. However, despite its sophistication it tends to be sensitive cell quality so a great deal of time is spent generating good conformant meshes both in pre and post processing results.
Thomas also takes over responsibilities for utilising the other enhanced capability using X-Flow provided by FlowHD. It allows QED Naval to reduce the pre/post processing time using Lattice Boltzman cells domain that is self-adaptive and easily controlled by the user in terms of vorticity in the model in the areas of interest. It combines this with fully transient, LES turbulent model which resolves the largest turbulence fluctuations in the flow while the smallest eddies are approximated for increased efficiency. The self-adaptive cell capability makes it much easier to conduct rigid body motions such as assessing tidal turbine performance characteristics. From the work conducted to date the tools were well validated using the Subhub performance model tank testing results and assessment of Tocardo’s T1 tidal turbine against their specified performance data.
QED Naval offer these capabilities to other marine renewable companies at competitive rates. The main advantage of this work is it can be used to determine what the design loads are on full scale structures without having to go to the expense of building a prototype. Hence, these assessments can minimise the technical and commercial risks of developing marine renewable structures and turbines.
QED Naval commissioned renewable energy consultancy, SgurrEnergy, to undertake an independent technical and commercial due diligence design review of the Subhub tidal turbine transport, installation and foundation system. It encompassed a review of analysis reports that had been produced as part of the feasibility and R&D studies supported by Scottish Enterprise. These include an analysis of all the tank testing results and the calculations of extreme loads, together with an assessment of the assumptions that have been used in scaling up to anticipated loads in larger device iterations. SgurrEnergy has also reviewed the tidal and wave loading numerical modelling reports that were based upon the tank testing campaign. This forms part of QED Naval’s detailed design process of the 1:4 scale technology demonstrator to be tested at Strangford Lough”.
The report also reviews the status of the tidal market and makes recommendations for QED Naval’s testing programme to validate the suggested performance and operation of the Subhub. These include a requirement to provide clear evidence to support the claimed reduction in CAPEX and OPEX costs compared to other transport and installation solutions, to demonstrate the potential increase in power density by accelerating the flow into the turbines, and to consider means of reducing the effects of tidal shear, veer and turbulence on the turbines installed on the Subhub.
The latest community scale version of the Subhub has now been frozen ready for build. Manufacturing outputs have been completed for the new modularised version of the Subhub. This allows the bare hull to be fabricated on the quayside and lifted into the water by a smaller, more available and lower cost crane.
After launch the newly designed modular solid ballast blocks can be easily lifted slotted into the bottom of the hull to provide the impressive stability characteristics of the Subhub during transit and installation.
The pressure cabinets to support the 3 x Tocardo T1 turbines have also been modularised to allow them to be slotted into the top of the hull once the main hull has been launched. This allows the cabinets to be quickly connected up to the generators whilst afloat. Access panels allow simple maintenance operations to be completed at sea.
Successful Installation & Retrieval Trials in Real Tidal Conditions
Recent testing of the Subhub operations model in high tidal flow conditions proved its ballast system capabilities and installation and retrieval methodology with great success. QED Naval were able to install the model on the seabed safely and in a controlled manner within minutes. The model was then secured on the seabed overnight before being recovered to the surface gracefully within an equally short time period and control.
Despite onerous wind, wave and current conditions experienced during testing, the Subhub coped admirably during the installation and retrieval trials. Scaling these extreme conditions to the prototype size, based on a 4.0m diameter turbine, would be equivalent to over 2m/s or 4 knots with a significant wave heights over 1.0m
Frontal profiles of turbine blades were added to the cross beam to simulate three turbines being installed on the Subhub; the blades acting against the current presented no issues.
Marine renewable engineering and design consultants