Tidal stream technology works in a similar way to wind turbines. The water flows over the hydrofoil sections (the ‘blades’) and creates ‘lift’ like an aeroplane wing. The blades then rotate driving an electrical generator. We are working with a number of leading tidal technology developers but have elected not to specify a specific technology manufacturer at this phase, taking a “technology neutral” approach to consenting the site. The consent application describes a range of different designs and configurations.
Most devices comprise of the following main components:
The Fixings/Base holds the structure in the required location so that it can counteract the forces of the sea and TEC acting on it. The fixings for Fair Head are likely to be based on drilling into the seabed by multiple smaller holes for pin-piles. Alternatively, a gravity base with sufficient mass to counteract the overturning forces on the TEC may be considered.
The Tidal Energy Convertor (TEC) converts the kinetic energy in the flowing water to electricity. We expect the devices to be 3-bladed open rotors driving an electrical generator either directly or using a gearbox to increase the speed of generator rotation to make it more suitable for electricity generation. The rotor is expected to be around 18m to 24m diameter, rotating around once every six seconds.
The Structure supports one or more TECs. Depending on the site resource conditions and expected variability in tidal flow, this structure may allow the TEC to rotate and align with the tidal flow for efficient operation. Part of the structure may pierce the surface of the water to allow access to equipment or aid navigation.
Understanding the nature of the tidal energy on the site is very important when calculating the potential amount of electrical energy (MegaWatt-hours). This knowledge informs the design of the devices ensuring they are built to withstand the various loads during operation and including extreme events.
Step 1 - Measure
Tidal measurements on site: Acoustic Doppler Current Profilers (ADCPs) have been placed on the seabed at various locations across the Fair Head site. They measure current speed and direction throughout the water column at predefined intervals. They are typically deployed for a minimum period of 28 days in order to acquire data over a full tidal cycle. Some ADCPs have also measured wave heights.
Step 2 – Model
Preparing a computer model to predict ‘whole site’ tidal characteristics: the model has been used to build a 2-dimensional flow model across the whole site. The data from the ADCPs has been used to validate the flow model.
Step 3 – Energy Map
From the model, we create an “energy map” by estimating the amount of raw marine energy across the whole site. The raw kinetic energy in the water has been calculated across the whole site to identify the areas of greatest resource interest. This kinetic energy is directly proportional to the cube of the flow (velocity), which explains why high velocity sites have significantly more energy than low velocity sites.
Step 4 – Array Design
Preparing a layout of tidal energy devices across the site – an array design. The level of knowledge on designs of tidal arrays is still evolving, and the experience gained from initial demonstrator projects will provide important learning points, which will help inform the layout of Fair Head Tidal.
Step 5 – Site Yield
Calculating energy production by combining energy map, array design and technology data. Once an energy map has been produced and an initial array design selected, the information will be used with tidal device performance data to calculate the amount of electrical energy produced by each device on an annual basis. The energy output for each of the devices is then aggregated to arrive at a total annual energy production for the site.
Analysis of resource data is ongoing but work done to date confirms that the tidal resource over a large part of the Agreement for Lease area would support a viable tidal energy project, subject to other economic and wider development factors.