Flowing water: A clean, reliable and renewable source of energy
Industry experts believe that hydrokinetic power plants would be capable of producing electricity on a commercial scale within the coming decade
Quamrul Haider
Solar and wind are currently the dominant sources of renewable energy. However, one of the common issues around these sources is that they are periodic and unpredictable. This makes it very difficult to compensate for those times when energy from the sun and wind is not available. Moreover, they have not been fully exploited partly because of incompletely developed technology and partly because transition away from dependence on fossil or nuclear fuel involves massive restructuring of the energy sector and huge new investment.
A source of renewable energy that has not been fully exploited is flowing water. The use of energy associated with water dates back thousands of years to the waterwheel mechanisms that were used to operate hammers in the ironworks, grind grain and saw wood. After the industrial revolution, the available potential energy of water stored at a height above a generator led to the development of hydroelectric power plants.
Hydropower creates no thermal pollution and does not produce greenhouse gases that have adversely affected the global climate. But it is not without its problems. One of them is that reservoirs behind dams fill up with sediment, giving a hydropower facility a short life span. Once a good site is destroyed by sediment, it is gone forever.
Theres another kind of hydropower known as hydrokinetic energy. As the name suggests, hydrokinetic power plants produce electricity by harnessing billions of kilowatt-hour of reliable, renewable, clean and sustainable energy of moving water continuously flowing down rivers and streams, or washing up on shores, that would otherwise just dissipate. In order to appreciate the power of moving water, just stand amidst breaking waves or try to swim against a rivers current!
There are primarily three types of water resources from which hydrokinetic energy could be used to generate electricity. They are wave, tidal and stream/river. Capturing the energy contained in the rise and fall of ocean waves is thought to have the greatest energy production potential. In addition to waves, researchers believe that the predictably regular ocean tides have the potential to provide us with a reliable source of clean electricity. And energy from free-flowing rivers can be captured without building any intrusive dams.
The power train of plants using hydrokinetic energy is similar to that of existing power plants. Only the source of energy is different. Conventional power plants use fossil or nuclear fuel to convert water into steam that turns the turbine blades which generate mechanical energy to run the generator that produces electricity. Hydrokinetic power plants use the energy of moving water to turn turbine blades.
The technology to tap hydrokinetic energy has developed to the point where it is being implemented on small scales by both public and private companies all over the world. The US Federal Energy Regulatory Commission has issued over 50 permits for tidal, wave and inland hydrokinetic projects with roughly 9,000 MW generation capacity. Three such projects are: a barge-mounted hydrokinetic power station on the Mississippi River in Minnesota, a power plant on Roosevelt Island in New York that will capture energy from both ebb and flood directions by yawing with the changing tide of the East River and a plant off the coast of Oregon that will harness energy of waves as they pass by.
On a global scale, at least 25 countries have initiated hydrokinetic RD activities. Some of these countries have successfully tapped hydrokinetic energy. Examples are the La Rance barrage dam, located on the estuary of the Rance River in Brittany, France, the Sihwa Lake Power Station in the west coast of South Korea, the MeyGen Tidal Energy Project located in the Inner Sound of the Pentland Firth off the north coast of Caithness, Scotland and the Annapolis power plant at the Bay of Fundy in Canada that generates electricity from the Bays record 43-foot tides.
Based on current project proposals, experts predict that United States could be producing 13,000 MW of power from hydrokinetic energy by 2025. This level of development is equivalent to displacing about two dozen dirty coal-fired power plants ‒ avoiding annual emission of nearly 86 million metric tons of carbon dioxide, as well as other harmful pollutants like mercury and particulate matter. The avoided carbon emissions would be equivalent to taking approximately 15 million cars off the road.
All energy technologies impact the environment, but all impacts are certainly not the same. In the case of hydrokinetic energy, the advantages far outweigh the negative impacts it would have on the marine environment.
Other than being clean, reliable and renewable source of energy with zero greenhouse gas emissions, hydrokinetic installations would have less visual aesthetic impact on the surrounding environment than wind turbines as most of the mechanical components of the various hydrokinetic devices will be located underwater. Besides, unlike traditional hydroelectric power plants, they do not require large dams and reservoirs.
Compared to the intermittent nature of other types of renewable energy sources, the natural sources of hydrokinetic energy are generally predictable and unaffected by changes in weather. The wave patterns for ocean based hydrokinetic systems can be accurately forecasted several days if not weeks in advance and the oceans tides will always reoccur every twelve hours or so because they are connected to the moons gravitational pull.
They would also provide benefits to the marine environment through the mitigation of carbon dioxide production which can lead to ocean acidification and a reduction in the risk of catastrophic spills associated with fossil fuel extraction and transportation.
Since the technology is in an early stage of development, and there are few devices in operation under the water, negative impacts on the environment are not well known and remain mostly speculative. Scientists at various government and non-government labs in the USA and elsewhere are studying the cumulative effects of hydrokinetic devices when added to other, existing stresses on aquatic systems.
Nevertheless, because hydrokinetic power generation relies simply on the extraction of energy from the natural velocity of water, these power systems could have some infrastructure and environmental impacts. The presence of underwater devices and their support structures could act as artificial reefs, thereby harming marine life and damaging their habitats. They may cause changes in hydrology, such as salinity, sedimentation pattern, water level and ocean/river currents, and thus navigability. Industry experts believe that hydrokinetic power plants would be capable of producing electricity on a commercial scale within the coming decade. They can serve as the base load power source, having profound effect on remote communities where traditional renewable sources may not be available, or if available, they wont be able to offer the same level of reliability.
Finally, even if we stopped burning fossil fuels right now, it would probably take the better part of a millennium before the Earths climate could return to normal. We can, however, limit the magnitude of climate change that is threatening our existence on this fragile planet by tapping into a variety of renewable resources. To that end, many countries have recognised flowing water as a potential contributor to their renewable energy portfolio.
The writer is a Professor of Physics at Fordham University, New York
