Tidal stream devices harness the energy available within tidal currents generated during ebbing and flooding tides. Tidal energy counteracts one of the significant barriers to most forms of renewable energy generation; unpredictability. By harnessing tidal energy, this enables for long term renewable energy generation to be predicted and using this, tidal generators could provide a source of renewable energy for baseload generation.
There are a number of ways to harness tidal stream energy, similarly to wind, the most common being Horizontal Axis Tidal Turbines (HATT), as well as Vertical Axis Tidal Turbines (VATT), Hydrofoils and Archimedes Screws [2]. With their successful application within the wind industry, the horizontal axis turbines have also begun to be the most applied tidal stream turbines. This has resulted in them being implemented by SeaGen in multiple projects and there are also plans to install 398MW of HATTs within the MeyGen project [3].
The tidal stream turbine that was chosen to base the calculations upon was the SeaGen-S 2MW system. This turbine was developed using data collected from the 1.2MW SeaGen model that was ran in Strangford Lough from 2008 to 2016 [4]. Use of this established turbine technology should provide a reliable source of information whilst having a comparable power capacity to other leading tidal stream technologies [3]. The technical data that was used can be found at [5].
To carry out the energy calculations for the turbine, first tidal stream data was extracted using QGIS. This provided the peak spring and neap current speeds as shown in the Table below. These values were then used to estimate the current speeds, at the chosen location Southwest of Islay, for an entire lunar cycle, which can be seen in Figure 1.
Peak Spring Speed | 3.05 m/s |
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Peak Neap Speed | 1.69 m/s |
These calculated current speeds can then be applied to power curve of the SeaGen-S 2MW system, shown in Figure 2, to estimate the power produced throughout the lunar cycle. This value could then be used to estimate the yearly energy generation of the system and calculate the systems’ capacity factor for the given location. These values are shown in Table 2, and the calculation spreadsheet can be found in the attached file “Tidal Current Calculations” below.
Lunar Cycle Energy Output | 508.9 MWh |
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Annual Energy Output | 6.29 GWh |
Mean Energy Output | 718.8 kW |
Capacity Factor | 0.36 |