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DEMOnstration for Tidal Industry DErisking

Periodic Reporting for period 3 - DEMOTIDE (DEMOnstration for Tidal Industry DErisking)

Reporting period: 2019-07-01 to 2020-12-31

Despite the success and growing scale of offshore wind, to ensure energy security and the carbon neutrality target by 2050 of the EC, it is vital for the energy mix to include several complementary renewable energy sources.
Tidal stream turbines harness the lateral flow of currents to produce clean, predictable renewable energy. Tidal stream projects can produce energy more consistently and predictably than alternative renewable energy sources, such as wind and solar, playing a key role in ensuring overall stability of Europe’s energy networks. Tidal stream offers an attractive alternative in areas where the visual impact of electricity generation sources is a concern. The ocean energy industry sees 100 GW of tidal and wave capacity being built in Europe by 2050, providing 400,000 jobs and supplying 10% of the EU’s current electricity needs.

The key barrier to the development of a tidal industry is tidal energy convertors are still an emerging technology and require significant government support for smaller, demonstration arrays to be built. Only through larger scale projects (>100 MW) can volume cost reductions be made for tidal stream to be competitive with offshore wind. To enable such scale-up, smaller <10 MW arrays need to be successfully demonstrated first to ensure investor and government confidence.

The DEMOTIDE project aimed to design, build and operate a 4 x 1.5 MW (6 MW) SeaGen U turbine array at the MeyGen 1B site in the Pentland Firth, Scotland, building upon the lessons learned from the successful installation and operation of the MeyGen 1A 6MW project (which has generated over 21 GWh to-date since its energisation in January 2017).
The DEMOTIDE Consortium united strong players: DEME Blue Energy, Atlantis Resources Scotland, Marine Current Turbines, GeoSea, Queen’s University Belfast and Innosea.
To de-risk the tidal industry, the DEMOTIDE project aimed to systematically focus on the key aspects of concern: technology, installation, operation and investors’ confidence, working towards standardisation and commercialisation.

The DEMOTIDE project concluded monopiles facilitate the use of a larger rotor diameter for a given hub height, as there is no gravity ballast around the base of the turbine creating flow interference. It has been indicated the rotor diameter can be increased to 20m, giving an increase in the energy capture area of almost 25% in comparison to the MeyGen 1A 18m rotor turbines.
For the outlined potential turbine improvements, the estimated the increase in generation is in the order of 100% with individual turbine generation increasing from the foreseen AEP of 3,000 MWh for the 1.5 MW device to potentially 7,000 MWh for the 2 MW device.

The optimum power marshalling concept for the tidal array was identified as a subsea marshalling hub to which the turbines would be connected via inter-array cables with a single export cable to shore. This designed concept is estimated to reduce CAPEX cost for a medium-sized array by 25%, and LCoE by 18%. It would minimise environmental impact due to the reduction of several export cables to one cable.
The DEMOTIDE project was active from 01/01/17 to 07/11/17 when it was suspended on the request of the Consortium due to the lack of vital UK government revenue support. The Consortium allocated considerable resources outside of the DEMOTIDE project to explore all alternatives to the anticipated revenue support to ensure the project could proceed. Ultimately, the DEMOTIDE project could not proceed and the Consortium decided to initiate the termination process.
The DEMOTIDE project produced four deliverables: Provision of site information report of the MeyGen site; Health, Safety and Environment Road Map; Report on foundation design and; Environmental Impact Assessment.
The DEMOTIDE project identified target areas to reduce the CAPEX (e.g. turbine, foundation, cable infrastructure P&M, installation), OPEX (i.e. designing the array with optimised O&M in mind) and maximise the vital revenues through generation optimisation. Comprehensive optioneering exercises were undertaken to shortlist concepts to take forward to the detailed engineering phase.
As part of the design and engineering activities, extensive efforts were made to characterise the MeyGen 1B site to provide the key parameters and requirements to design and build the optimum tidal array, including micro-siting of turbines for optimal resource capture and ensuring minimal environment impact and safe operations.

To optimise O&M, by reducing necessary operation times and costs, the monopile-turbine interface was envisaged to be a standardised wet-mate transition piece connection enabling quick-release and redeployment underwater for a range of OEMs to connect their tidal device. The cable management system would be integrated in the foundation.

As part of the foundation review and concept design, the optimum installation methodology was investigated considering all best available technologies and site characterisation, concluding the monopile foundations would be installed using topside drilling from a jack-up platform (JUP) with a preliminary micro-siting and positioning study undertaken. JUP or DP vessel were identified as the optimum methods for installing turbines. DP vessel are optimal for installation of offshore electrical infrastructure (marshalling hub, intra-array cables and main export cable to shore) and for O&M operations.

The integrated wet-mate connection cable management system concept designed by the DEMOTIDE project aimed to enable efficient O&M operations, potentially significantly reducing the O&M cost during the lifetime of the project by >50%.
Commonly deployed foundations for tidal device demonstration are gravity-based foundations (GBFs) as the technology is proven and relatively quick to deploy. Following the detailed optioneering and engineering exercises, considering a broad range of possible foundation technologies, installation vessels and methodologies, monopile foundations were considered the preferred solution for commercialisation. GBFs have proven their suitability for tidal stream device demonstrations, however, it is believed in the tidal industry, monopiles will be deployed for project optimisation for commercial and cost competitive tidal projects.
The monopile design produced by the DEMOTIDE project is a clear move beyond the state of the art with the integration of the cable management system, universal wet-mate transition piece and overall a key step towards standardisation in of the industry and commercialisation. Atlantis Resources estimate their subsea marshalling hub concept could reduce project CAPEX by ~20%.