Hydrokinetic Power

What is it?

The current energy crisis is one of the most widely discussed issues in the news today. While gas prices most obviously illustrate growing trends towards higher energy costs, the effects can be seen in every energy sector. Because of this, numerous pursuits are being made towards alternative sources of power. These sources may be nonrenewable, such as nuclear energy, or renewable, such as solar, wind, and water power. Traditional dam turbine hydro power is one area of renewable energy that has been very effectively implemented around the world. A second type of hydro power, termed hydrokinetic power, has proven potential to make a significant and lasting impact.

Forms of hydrokinetic energy can be divided into three forms: tidal, wave and stream/river. Extensive research is being completed in all areas, and the technology has developed to the point where it is being implemented on small scales by both public and private companies in areas all over the world. The applications of systems vary in terms of their configurations, which are as diverse as the locations where they are implemented.

Hydrokinetic power differs most notably from the traditional hydropower systems by harnessing the kinetic energy possessed in velocity of water, instead of harnessing the potential energy arising from pressure differential developed in dam. This creates the ability to harness energy without structures that are expensive, time consuming and labor intensive to build, and very intrusive to the surrounding area. In this paper, various forms of current and future hydrokinetic systems will be summarized, along with the associated benefits and drawback of each, and of the technology as a whole.

How does it work?

Hydrokinetic power in river applications is extremely analogous to wind power. Simply, a turbine of some form is placed directly in the flow path of the fluid which causes rotational motion and electrical power. This form requires no impoundment of water [1].

While a simple concept, the implementation has taken on a variety of forms which all seek to increase the output wattage output and efficiency in various types of flow. Factors affecting these parameters include the kinetic pressure head and the turbulence. Also, slow, deeper flows up to 100 feet must be handled differently than fast shallow flows of less than 10 feet. The array of physical implementations has created an equally large variety of solutions. Sizes of power harnessing units for example, range from several meters to 30 meters or more in diameter. Accordingly, the weight of the units can range from a few hundred pounds to many tons. While different systems and applications are being investigated, a common denominator is the fact that the power output is directly related to the velocity of the flow [2].

One area that has undergone particularly intense growth in interest is wave energy. There are several methods for harnessing the kinetic energy of waves. One design, the Pelamis, consists of a caterpillar-like series of tanks that produce energy based on their relative vertical displacement relationship to each other. The waves cause fluctuations in these displacements which move pistons that pump oil through tubes that move power generating turbines.

Another system, the Aquabouy, focuses on the pressure drops produced when a buoyant object pulls away from a fixed unit because of the force of the harmonic pull rom the waves. This pressure drop sucks water into the system which turns a power generating turbine. Aquabouy systems generally consist of dozens of units that work in a type of unified web of power generation. Other buoy systems that are being researched use the magnet-coil form of energy production where the coil system is buoyant enough to move up and down relative to the magnetic coils to generate small amounts of electricity.

Many new systems are being created as a way to harness ocean tidal currents in a way other than from current tidal power energy plants that are essentially just dams that use common hydro-electric generating methods for tidal flows. Tidal energy is primarily the harnessing of the kinetic flows of the tides coming in and receding. The new system designs usually use stand alone fans that spin turbines to generate power. Another method of tidal power generation is simply a harnessing of the simple harmonic motion of the overhead waves caused from tidal currents[4]. They are completely dependent on the moon’s gravitational pull of the water inland. The systems are generally only applicable in areas of intense tidal influence, in narrow waterways and bay entrances. They can range from only a couple meters tall to systems that reach heights of 50 meters[4].

Why is it being investigated?

Clearly, hydrokinetic power is a carbon free, low impact and domestic source of renewable energy. Moreover, a recent study by the Electric Power Research Institute (EPRI) found that by 2025, the U.S. could develop a minimum of 13,000 megawatts of river and ocean based hydrokinetic power. Earlier estimates suggested the U.S. could potentially double its hydropower output with newly developed technology. This is enough energy to power roughly 12 million homes [3].
Another assessment, done by the Idaho National Laboratory stated that nearly 30,000 MW of hydropower exist within the United States, and that over 60% of this energy is available in western states, and could be harnessed without any additional dams [2].

Wave energy follows the similar principals of other hydro kinetic power designs. It is completely renewable, and because of the density of water compared to the density of air, it is expected to be able to harness considerably more energy over smaller areas. These systems are also desirable because of their ability to be unseen. The systems are generally stationed miles offshore and away from public interest, unlike the wind turbines that can be seen for miles in any direction.

When considering tidal energy research, some coastal areas have such intense tidal pulls that it would seem wasteful to ignore the potential energy that could be harnessed. The Alaskan coast alone has two tidal areas that alone could produce as much as 10,000 MW of electricity an hour. These new tidal units would be similar to the wave power generation systems in that they can be completely out of public sight[4]. The tidal systems can be completely submerged many meters below the water and can pose little to no danger to area wildlife.

What are the drawbacks and challenges?

Though there are discrepancies between studies, it remains clear that abundant potential exists. One may ask then, why the technology has not passed its current level. Most importantly, the technology is being stymied by the initial startup costs. These costs are associated with research and development and initial investment costs. This is a common factor to all emerging energy technologies, and one that is significantly affected by a fluctuating economy.

Furthermore, traditional private financing models require payback periods of 5-7 years, while in most cases it can take up to 3 years for a project to receive licensing after a working prototype demonstration has proven successful. Instead, “aggressive front-end project financing and project buy-downs are needed to get the early-stage commercial projects in place and on the way to improving a technology to a cost-competitive, commercial scale [3].”

Various existing companies have performed economic feasibility studies, but have chosen to keep their findings proprietary. Public findings include The Commercial Prospects for Tidal Stream Power, (2) prepared in 2001 by Binnie Black & Veatch for the UK Department of Trade and Industry, and the March 2004 work, The Costs of Generating Electricity, by The (UK) Royal Academy of Engineering. These studies have both produced projected initial costs, which include manufacturing investments, to be between 8 and 10 cents per kWh. Since current wind technology has produced electricity as low as 4 cents per kWh, it is not unreasonable to expect similar results from well placed hydro generators [3].

Additionally, the “best” method for harnessing the energy has not been determined. This is again reflected by the diversity seen in prototype designs. Only time and continued research will lead to increased understanding of the factors involved with this new form of power generation, and the factors involved with creating efficient harnessing techniques. This new technology also faces complications when attempting to integrate itself with the existing power grid. With power generation mainly occurring underwater, in remote areas, or possible miles off shore, there becomes an additional technological and financial hurdle to be overcome. Solving this issue will require the integrated teamwork of traditional utilities with hydropower developers.

Finally, the utilities are a highly regulated industry. When a site is being investigated for a potential application, up to 19 attributes are considered, including fishery, geologic, historic, recreational and scenic factors. With no precedence other than wind energy to guide future developments, projects that have reached the point of implementation are stymied by bureaucratic obstacles. Organizations in power must first realize the inherent benefits of the technology before real progress can be made [3].

With regards to wave power drawbacks, the primary research being done is not commercial; it is primarily being worked on by universities.[4] Most areas with the ability to produce a constant source of kinetic wave energy are several miles off shore and would require expensive copper cable of ridiculous lengths. More domestically, the United States government funds all types of renewable energy production with the exception of wave energy; it is a particularly underfunded field of research considering the apparent need for renewable energy. Tidal energy drawbacks are similar, but they have even greater problems with achieving desired funds or interest.

Where is it currently being used?

Even with the discussed challenges, there has been unhindered growth and excitement surrounding this topic. Currently, there are no cases of projects that are successfully providing power to an electrical grid. Research has shown though, that serious interest exists, and that prototype development is rapidly occurring.

To name some examples, Free Flow Power is proposing to install (for a cost of $3 billion dollars) hundreds or possibly thousands of turbines between St. Louis and New Orleans in the Mississippi River. This would equate to a power output of 1,600 MW. The company has successfully acquired preliminary permits to test units in 59 different locations in the river. Verdant Power has proven to be the most successful in the States, as they have completed turbine power generation testing the New York’s East River. While all of the prototypes have failed and funding is running low, the company has made strides toward future successes. Two New Hampshire companies, Oceana Energy and Underwater Electric Kite Company have both acquired permits to run tests in the Piscataqua River, but no activity has been reported to date.

Wave energy is primarily being used in the UK. Great Britain has an incredible amount of potential "wave farms" and has a significant amount of projects underway. In Norway, several programs have begun construction of wave energy harnessing devices. The 500 KM Norwegian coast specifically allows for consistent large wave occurrence and is ideal for more wave farms.

The Strangford Laugh channel in the UK has a fully operational 1.3 MW generating tide turbine. New Zealand is currently putting in an incredible 200 MW tidal energy production system that should be fully operational by 2012. This will consist of 200 1 MW underwater fan turbine generators in an underwater tidal “farm.” It is the largest tidal generating project being undergone in the world.

What is the Future Outlook?

Despite the apparent need for these energy resources, the outlook does not appear to be stellar. Some analysts put wave power around 20 years behind wind power. Others say it is barely 5 years behind. Wave power is half as efficient as wind power, but it is only because of its early stage of development. When compared to wind energy when it was as primal, wave energy is considerably more efficient. It is assumed that the cost of wave energy will significantly decline as the systems develop. There is an incredible about of potential in hydrokinetics.[4] Around 60% of the world’s population’s lives within 50 miles of an ocean, allowing for the potential for wave power to be a perfect candidate for renewable power focus.