Energy can be harnessed from the tides in two ways: using the change in height of the tides (potential); and using the flow of the water (kinetic).
Tidal power is very sensitive to speed. The power output varies as the cube of the speed. In other words, if the water flows twice as fast, it makes eight times the power.
Also, tidal turbines do not have to spin as fast as windmills to generate power, because water is roughly 800 times more dense than air.
Tidal power technology is constantly evolving. However, the most common technology today can be classified into three main categories:
The in-stream tidal turbines tested at FORCE use the flow of the water as the source of power. Each of the turbines is designed to use the flow of the passing water to turn an impellor, just like a windmill. Each turbine is different in how it manages this but, in the end, each uses the rotation of its turbine to turn an electrical generator.
Designed to operate in the open flow of water in the Minas Passage, the turbines have to operate in a range of water speeds, from zero to a maximum of 10 knots. As water speeds can vary from the surface to the sea floor, test conditions for each turbine will differ slightly and depend on both the site location and the depth at which they are positioned.