Following an extensive project selection exercise in the waters off Wales, Marine Current Turbines Limited (MCT) are seeking to install a marine current turbine generator array of up to 7 units known as the Skerries Tidal Stream Array off West Anglesey.
The total capacity of the proposed Skerries Tidal Stream Array project is 10MW.
The location for a pre-commercial demonstrator farm is proposed to be located in the Sound between the group of rocks and islands known as the Skerries and Carmel Head on mainland Anglesey, less than 1km from the Anglesey coast, in approximately 20 to 40m water depth. The project comprises up to seven twin rotor machines consisting of a central monopile with two 18-20m (approx) diameter rotors mounted on either side of an axial cross-arm, as illustrated in Figure 1, which indicates the proposed structure above and below the surface, and dimensions of the turbine.
In addition to the offshore device infrastructure including inter-array and export cables; ancillary onshore works and works in the inter-tidal zone, are required to connect the array to the electricity distribution network.
A new subsea cable will bring the generated electricity to shore. The landfall location has yet to be decided but is likely to be close to Wylfa, subject to feasibility work undertaken by SP Power Systems (Manweb).
This project forms a significant part of MCT Ltd's development programme intended to test the practical viability of deploying the Seagen turbine in a small array. It is proposed that the turbine array will be installed and operated for up to 25 years, where it will serve as a test case for the development of the technology as part of a programme of further multiple unit arrays.
The principle used by this technology is analogous to an 'underwater windmill', with the passing current turning large propeller-like rotors which drive generators from which electricity can be sent ashore through marine cables. As water is much denser than air, the currents needed to generate useful power are quite slow, around 2 to 3 m/s (4 to 6 knots). Consequently, the rotors of the tidal turbines are relatively slow turning compared with wind turbines, typically at speeds of around 10 RPM, with tip velocities of no more than about 12 m/s (10.4 m/s based on 20m blade diameter).
Advantages of tidal current turbine power generation are:
- it produces no pollution;
- energy is delivered predictably (the tides can be predicted many years in advance);
- the potential exists for this source to make a significant and cost-effective contribution to future energy needs
Support for the development of energy resources such as tidal power is a key part of the UK government's strategy to develop renewable energy as a means to combat atmospheric pollution and mitigate climate change as agreed under the Kyoto Protocol. The rationale for developing this technology stems from the need to address escalating global energy consumption combined with the need to develop clean renewable energy (in line with the Protocol). However, key considerations are the socio-economic and environmental constraints associated with the construction and operation of large renewable energy production schemes from marine resources, due to the increasing difficulties associated with implementing large-scale renewable projects on land.
Acknowledgement: This article was identified by the Crown Estate Wave and Tidal Knowledge Network.