In-stream tidal units convert the energy of tides and currents into power – a
type of hydropower which has operated successfully for decades. No matter what you call it -- wave, in-stream tidal, river current, or hydro turbines; or where it sits -- sitting on the river bottom or suspended from a barge -- the technology has proven itself. What has remained more elusive is the much-needed transition from
Subsidies to commercial financing. At the 5th Annual Small Hydro Conference in April 2013 in Vancouver, British Columba Chris Campbell of Marine Renewable, Canada, explained the two principal
Advantages of in-stream/tidal units: 1. Water has a high energy density -- the energy density from water is up to 50 times that of wind, and 100 times that of solar PV. For example, in a 2 knot current, each square meter of flow yields up to 500 watts of electricity. This means a wind turbine would require a 400 km per hour breeze to generate the same amount of power as the 1.5 MW Siemens generators in Strangford Laugh
(Described below) does in in a 5 knot current; and Predictability and reliability – the flow and timing ofTidal streams are much more predictable and reliable than either wind or solar.
The original approach to using energy in the tides was to use tidal barrages (height difference = power), but now the emphasis is on tidal stream, where the energy is captured in ebb and flood currents as the tide changes. As shown in Figure 1, this means the most favorable sites are passes and headlands where tidal channels are created. This technology has proven itself. The River Rance scheme in France, inaugurated by President Charles de Gaulle, was connected to the grid in 1967.
A Nova Scotia plant, on the Annapolis River, has recently been rehabilitated and updated after two decades of operation. The Siegen plant, located in a narrow passage on the Stanford Lough in Northern Ireland (see Figure 2), hasBeen in operation since July 2008: with very few problems it has pioneered the use of tidal currents. Recently many new Canadian sites were identified, including:
- Nova Scotia (Bay of Fundy, anywhere from 300 to 2,500 MW potential);
- British Columbia (Vancouver Island – 62 sites, average 58MW potential; North Coast—18 sites, average 20 MW potential; or Haida Gwaii—9 sites average 9 MW potential), and
- The arctic has even more! The recent trend is to find new sites where the first real power plants can be demonstrated (5- 100 MW). Locations under examination include: Scotland (especially Pentland Firth), France (principally northern Brittany) and Maine (Half Moon Cove and other areas close to the Bay of Fundy).