What is Hydrokinetic Power
The power of moving water is obvious to anyone who has stood amidst breaking waves or struggled to swim against a river’s current. New technologies can enable us to harness the might of moving water to help light our homes and keep our ice cream cold in the freezer without building new dams that can have major impacts on wildlife and water quality.
The use of water power dates back thousands of years to the water wheels of Ancient Greece, which used the energy in falling water to generate power to grind wheat. We now are presented with an opportunity to develop a new generation of water power, one that will harness the abundant energy of our oceans and rivers.
Hydrokinetic technologies produce renewable electricity by harnessing the kinetic energy of a body of water, the energy that results from its motion. Since water is 832 times denser than air, our tides, waves, ocean currents, and free-flowing rivers represent an untapped, powerful, highly-concentrated and clean energy resource.
Estimates suggest that the amount of energy that could feasibly be captured from waves, tides, and river currents in the US alone is enough to power over 67 million homes. Based on current project proposals, experts predict that the country could be producing 13,000 MW of power from hydrokinetic energy by 2025. This level of development is equivalent to displacing 22 new dirty coal-fired power plants, avoiding the 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 in 2025 would be equivalent to taking 15.6 million cars off the road.
All energy technologies impact the environment, but all impacts are certainly not the same. As we choose which energy resources to develop, we must weigh their varied costs within the context of the existing hazard of global climate change. Studies are underway to investigate the potential impacts of harvesting wave and current energy on wildlife and the environment; however, it is clear that these technologies could help reduce the greenhouse gas emissions that are causing dangerous global warming. There is a need to weigh the environmental impacts of hydrokinetic technologies against the environmental and impacts of other available energy technologies, keeping in mind the costs of fossil fuels on air pollution and water pollution as well as global warming, and the need to have sufficient low-emission alternatives.
The hydrokinetic resource
There are a number of types of water resources from which it is possible to generate electricity from kinetic energy. Capturing the energy contained in near and off-shore waves is thought to have the greatest energy production potential amongst these hydrokinetic options. The rise and fall of ocean waves is driven by winds and influenced by oceanic geology. The promise of waves as a power source comes from both sheer resource availability and a relatively advanced technological development status. Extracting only 15% of the energy in coastal waves would generate as much electricity as we currently produce at conventional hydroelectric dams. Much of this wave potential is found along our Pacific Coast, near big cities and towns like LA, Seattle and Vancouver.
In addition to waves, researchers believe that ocean tides hold promise as an energy resource. Each change in the tide creates a current, called a tidal stream. These predictably regular tidal streams have the potential to provide us with a reliable source of clean electricity without building the dams, or barrages, that have been part of many existing tidal projects developed in some other countries.
Other stream resource prospects for hydrokinetic energy development include ocean currents, such as the Gulf Stream, which result from winds and equatorial solar heating; free-flowing rivers, from which energy capture is possible without any intrusive dams; and even constructed waterways, such as irrigation canals.
While stream-based hydrokinetic energy research is not as evolved as its wave energy counterpart, initial estimates expect these water resources could fulfill all of the electricity needs for an additional 23 million typical homes. Stream hydrokinetics could prove to be a particularly valuable resource for regions with lower wind energy potential, especially in the US Southeast; numerous permits have been granted by the Federal Energy Regulatory Commission (FERC) allowing pilot project development and technology impact research along the lower Mississippi river. Additionally, capturing just 0.1% of the available energy in the Gulf Stream could supply Florida with 35% of the state’s electricity needs.
Beyond the sheer size of the resource, hydrokinetic energy is attractive for its predictability; wave patterns can be predicted days in advance, and tides for centuries. Additionally, while waves and ocean currents are variable, they can provide continuous power, which is not possible from variable-output renewables like tidal streams, wind, or solar power. Since the kinetic energy held in a stream is related to its speed cubed, extracting the most electricity from each hydrokinetic project will depend heavily on site selection.
A water current with double the speed contains eight times as much energy as one moving just half as fast!
Policymakers across the globe have taken notice of the potential of hydrokinetic energy, and have begun to support its development through legislative and monetary means; ocean energy is an eligible resource for credit under renewable electricity standards in many countries
The technologies developed to generate energy from waves and currents, called hydrokinetic energy conversion devices, are generally categorized as either wave energy converters or rotating devices. Today, many of these devices remain in development, though some fully permitted pilot devices are already deployed on-site.
The industry is rapidly progressing through development of “wave parks” and turbine arrays capable of delivering clean, renewable electricity to the grid on a commercial scale. There are numerous promising configurations within each of these technology categories, and the lack of a clear leader today emphasizes the need to support further engineering studies and pilot deployments to establish the most cost-effective and environmentally sound options.
Rotating Energy Devices
Rotating devices capture the kinetic energy of a flow of water, such as a tidal stream, ocean current or river, as it passes across a rotor. The rotor turns with the current, creating rotational energy that is converted into electricity by a generator. Rotational devices used in water currents are conceptually akin to, and some designs look very similar to, the wind turbines already in widespread use today—a similarity that has helped to speed up the technological development of the water-based turbines. Some rotational device designs, like most wind turbines, rotate around a horizontal axis, while other, more theoretical concepts are oriented around a vertical axis, with some designs resembling egg beaters.
Union of Concerned Scientists - July 14, 2007
The Swordfish Design
The Swordfish 'Patent Pending' design is unique within all other rotating device designs. It is indeed a horizontal axis design however; unlike other designs in this genre where the rotor spins within the stator requiring a geared mechanical transmission apparatus, Swordfish power is achieved through the rotation of the rotor around the stator delivering a greater power-to-weight ratio through direct drive.
Swordfish is a far more efficient system!
Environmental impacts and facility siting
While the generation of electricity by hydrokinetic devices does not produce harmful air emissions, like the greenhouse gases linked to global warming, further research is necessary to determine what other types of environmental impacts may result from tapping the energy in waves and currents. The extent of these local impacts is important to evaluate, and appropriate caution should be taken in the development of regulations surrounding hydrokinetic energy development.
Scrutiny of hydrokinetic energy projects must be placed in the context of our wider energy and electricity generation mix. Specifically: governments must shift its energy resources away from the fossil fuels that are contributing to global warming, price volatility, and energy insecurity, and towards a clean, renewable, stable, homegrown energy supply that will create domestic jobs and save consumers money.
As we continue to monitor the environmental and competing-use impacts of the hydrokinetic technologies producing electricity in our waters, we must also give proper recognition to the current and ongoing problem we face of climate change.
Choosing the most suitable locations for wave parks and turbine arrays depends on a number of impact considerations and site characteristics, including:
Environmental – the effects of bottom-moored devices on the habitats of benthic animals and plants, like oysters, clams and sea grass; the potential for fish strike or impingement on a device; and whether a full-scale array of devices could create significant noise, hinder the movement or migration of aquatic animals, or even alter hydrologic and sediment regimes.  However, some studies indicate that these impacts are likely to be minimal where appropriate care has been taken in site selection and project design. Further, any adverse impacts can be minimized through study of past pilot projects, and by drawing upon research of other marine fixtures, such as oil platforms.
Economics – the cost of electricity generated will be a function of the power density of the stream (kW/m²), the distance the electricity must be transmitted to reach consumers, the ease of access to a site for ongoing maintenance and monitoring, and the availability of tax incentives for project financing and electricity production. Fundamentally, sites with manageably stronger currents, will provide the lowest cost hydrokinetic electricity.
Competing uses – Fishermen, shipping vessel operators, recreational boaters, and coastal community groups have expressed concerns about the effects of hydrokinetic energy developments on their own usage and enjoyment of our waters. Their representatives have taken part in the negotiation process as potential development sites are explored, and will continue to play an important role in project placement and design. Our water resources already accommodate a wide range of uses. Subsequent to proper environmental and siting review, hydrokinetic energy is poised to be safely added to this mix, generating much-needed clean electricity without hindrance to other usages.
Hydrokinetic energy development is rapidly progressing, both technologically and with the help of supportive policies that recognize the critical role this renewable energy resource can play in a warming world. Harvesting the motion of our tides, rivers and oceans can be a part of an affordable and sustainable solution to reducing our dependence on fossil fuels, and the impact they have on environmental and public health.