Artist’s conception of a wave farm of 750-kW Pelamis wave converters.
Chemical and Engineering news has an excellent overview of the various technologies being developed to create electricity from moving water. The primary methods are wave and tidal.
Waves are powered by winds and uneven solar heating, he says, and wave energy works best in ocean depths of at least 50 meters, before waves lose energy to the friction of a shallow sea bottom.
There are many designs being tested now. Some will go mainstream.
Natural constrictions can also help funnel the tidal flow to turbines, he notes, pointing, for example, to the mile span under the Golden Gate Bridge, which results in powerful currents as the huge bay fills and drains twice a day.
Imagine how much power could reliably be generated every day with masses of underwater turbines under the bridge.
A distant possibility is ocean thermal
Thermal energy … uses differences in temperature between near-surface and deep-ocean waters to generate power [and requires] huge investments and a long payback.
This is the same principle as geothermal, but on a vastly larger scale.
In just a few years, we will hopefully see enormous amounts of new wave and wind energy power – and solar and wind power as well.