While hydropower deals with energy produced from falling water, hydrokinetics is the study and development of energy harnessed from the natural power of water movement: waves, tidal streams, natural flow of rivers and ocean currents. New technologies can enable us to harness the kinetic energy that results from its motion. Based on current project proposals, experts predict that the country could be producing 13,000 MW of power from hydrokinetic energy by 2025. These projects could reduce carbon emissions by avoiding 86 million metric tons of carbon dioxide. Congress’ passing of an energy appropriations bill for 2013, which allocates $44 million for marine and hydrokinetic research, demonstrates that this source may prove a powerful option amongst the alternative energy options.
Of all the hydrokinetic options, waves are thought to have the greatest energy production potential. The powers of waves are harnessed through energy conversion devices such as wave energy converters. One common example of a wave energy converter is the oscillating water column. Waves enter and exit a partially submerged collector from below, causing the water column inside the collector to rise and fall, which creates a piston that drives air above water into a turbine.
In addition to waves, ocean tides may also be a useful energy resource. Each change in the tide creates a current, called a tidal stream. Given the predictability of tidal streams, they are also likely to provide a reliable new source of clean electricity. Other stream resources include ocean currents, such as the Gulf Stream, and free-flowing rivers. These stream-based hydrokinetic resources will likely be more prevalent in regions with lower wind energy potential, such as in the Southeast. As of March 2008, 36 preliminary permits have been granted by FERC for projects along the lower Mississippi river. The energy conversion devices used for the flow of water are rotating devices, which capture the kinetic energy of a flow of water as it passes across a rotor. The rotor turns with the current, creating a rotational energy that is converted into electricity by a generator. The devices are similar to wind mills used to harness wind energy.
One major advantages of hydrokinetic technology as compared to traditional hydropower is that is does not require the building of a dam and therefore, there is minimal impact to surrounding areas. Dam construction may cause the depletion of river flow, the displacement of local communities, and can often damage entire ecosystems. In addition, unlike other forms of renewable energy sources such as wind and solar, areas where energy can be harnessed from hydrokinetic energy are easy to predict. Tidal and current forces, as well as the strength of river flows, stay relatively constant in a given area so developers can focus on these regions for installing hydrokinetic technology. Wind patterns are harder to predict and wind mills may be constructed in areas with relatively low wind forces.
To date, there have been few studies on the environmental effects of hydrokinetic technologies. Most considerations of the environmental effects have been in the form of predictive studies and assessments that have not been verified. Some of the possible anticipated environmental effects include alteration of current and wave strengths, alteration of sediment transport and deposition, generation of electromagnetic fields, and interference with animal movements and migrations, including entanglement.
Despite these environmental unknowns, investing in hydrokinetic technologies will certainly reduce the emissions of harmful greenhouse gases and in the near future, may prove to be a major player among the clean energy sources.