There are two types of tidal energy extraction methods, one using the flow of tidal currents and one using a head of water formed by the rise and fall of the tides. one Either way, it is in effect lunar power. The worldwide potential for tidal power is estimated at 800 TWh a year, equivalent to 3-4% of global power consumption.
Tidal current, or in-stream tidal technology captures the energy in fast-flowing tidal currents, using submerged turbines at locations where the current is constricted, and hence more powerful. Tidal power generation varies significantly during each day, but it does so in a predictable manner, so it can be easily integrated into the grid.
Another approach to extract energy from tides focuses on the actual rise and fall of the tide. Tidal range technologies use some type of holding basin such as a dam, barrage, or lagoon structure. Water flowing from the high side to the low side of the structure energizes a turbine, much like a hydro dam in a river. Barrages are essentially dams across the full width of a tidal estuary. When the tide goes in and out, the water flows through tunnels in the barrage and generates electricity. Nova Scotia Power has been operating the Annapolis Tidal Station in Annapolis, Nova Scotia since 1984—a facility which uses tidal range. It has a capacity of 20 megawatts (MW) and a daily output of roughly 80- 100 megawatt hours (MWh), depending on the tides.
Extensive resource assessments have been completed in BC and across Canada looking at the tidal energy and in-stream river energy potential of the oceans and rivers.
In September of 2006, Clean Current Power Systems installed a tidal turbine at the Race Rocks ecological station. The turbine, in combination with a solar and battery system, became the first complete ocean energy power system displacing diesel on the island. The Race Rocks turbine was removed in 2011, however a number of other potential tidal energy sites are currently under investigation in BC.
The government of Nova Scotia is actively pursuing the development of tidal energy, primarily due to the enormous resource potential of the Bay of Fundy. The Fundy Ocean Research Centre for Energy (FORCE) was created as a world-class test centre for in-stream tidal technologies, with permitted common infrastructure, collaborative environment management, and four cabled “berths” for technology interconnections.