Tidal Power is the extraction of energy from tidal currents, flows and streams to produce electricity. These flows primarily result from the gravitational effects of the sun and the moon on the Earth’s oceans. These effects cause the rise and the fall of the ocean which then cause currents by interacting with a variety shoreline shapes and sea floor contours. While the oceans present challenging environments in which to work, tidal power meets these challenges to achieve some important advantages over other renewable sources of energy.
Tidal power is very variable over a short time frame, typically peaking once or twice per day, but is extremely predictable over many years. The tidal cycles usually include the following phenomenon:
The sea level rises over several hours, covering the intertidal zone. The water rises to its highest level, reaching high tide. The sea level falls over several hours, revealing the intertidal zone. The water stops falling, reaching low tide.
The typical patterns in the tides are a twice daily variation (semidiurnal). There is also a difference between the first and second tide of a day. There is also a spring-neap cycle that repeats every 7.5 lunar months. These cycles vary annually, repeat themselves over a period of several years, and are as predictable as the orbits of the earth, sun, and moon.
Tidal power is a denser form of energy than either wind or solar power. Seawater is 832 times as dense as air and is not compressible. This means that more power is available per square meter in tidal than for wind or solar. Like wind, tidal power is a function of the velocity of the current flow cubed. As tidal flows peak, the power extracted increases geometrically. This energy density is further leveraged by the massive size of the ocean and the scale of the currents produced with the change of the tides.
Tidal installations will achieve a larger scale than most river sources because of greater working depths and the size of productive sites. While there will be many river projects that utilize BEC’s technology, none of them will achieve the same scale as the largest tidal power installations. And given the greater energy densities, this will make tidal power competitive with current electricity prices for a clean and predictable source of energy.