Introduction to Hydrokinetic Energy
Hydrokinetic devices are powered by moving water and are different from traditional hydropower turbines in that they are placed directly in a river, ocean or tidal current. They generate power only from the kinetic energy of moving water (current). This power is a function of the density of the water and the speed of the current cubed. The available hydrokinetic power depends on the speed of the river, ocean, or tidal current. In contrast, traditional hydropower uses a dam or diversion structure to supply a combination of hydraulic head and water volume to a turbine to generate power. In order to operate, hydrokinetic devices require a minimum current and water depth.
How Does Hydrokinetic Energy Work?
As water flows through a turbine or other device, the kinetic energy of the flowing river, tidal fluctuations, or waves is converted into electricity by the device.
As mentioned in the above introduction, hydrokinetic devices require a minimum current and water depth. The minimum current required to operate a hydrokinetic device is typically 2-4 knots. Optimum currents are in the 5-7 knot range. Water depth is an important factor in the total energy that can be extracted from a site, since rotor diameter is dependent on adequate water level above the installed device. Hydrokinetic devices are ideally installed in locations with relatively steady flow throughout the year, locations not prone to serious flood events, turbulence, or extended periods of low water level.
Challenges in Hydrokinetic Energy
Among the challenges in hydrokinetic energy is the presence of glacial silt in Alaska waters, especially Cook Inlet. Over time, silt and other sediments in the water flowing through hydrokinetic turbines can erode the machinery. In addition to this, the migration of fish and marine mammals, ice and other debris, as well as river and ocean bed stability, must be taken into careful consideration
Hydrokinetic Energy in Alaska
Alaska has significant potential for hydrokinetic development in both rivers and tidal basins. Most inland communities in Alaska are situated along navigable waterways that could host hydrokinetic installations, and Alaska, with 90% of the total U.S. tidal energy resource, is home to some of the best tidal energy resources in the world. While there are obvious opportunities, there are also significant environmental and technical challenges (see below) related to the deployment of hydrokinetic devices in Alaska’s rivers and tidal passages. Some of these are common to installations in any location. Other concerns are more specific to Alaskan waters. As of 2008, hydrokinetic devices are considered pre-commercial. The Yukon River Inter-Tribal Watershed Council installed a 5 kW New Energy Encurrent turbine in the Yukon River at the community of Ruby for one month in 2008. A 100 kW UEK turbine is planned for installation in the Yukon River at Eagle in 2009. The New Energy EnCurrent machine, in 5 and 10 kW size, is available for purchase from ABS Alaska in Fairbanks, and New Energy Corporation is developing 25kW, 125kW, and 250kW devices as well. This technology is still being refined for Alaskan applications. Its performance is unproven.
Hydrokinetic devices typically use vertical or horizontal axis turbines similar to those developed for wind generation; however, because water is approximately 850 times denser than air, the amount of energy generated by a hydrokinetic device is much greater than that produced by a wind turbine of equal diameter. In addition, river and tidal flow do not fluctuate as dramatically from moment to moment as wind does. This predictability benefit is particularly true for tidal energy. It can be predicted years in advance and is not affected by precipitation or evapo-transpiration.
Hydrokinetic Technology in Alaska
In Alaska’s riverine environments, water flow fluctuates, often dramatically, on a seasonal basis. Snowmelt from glaciers and seasonal snow accumulation contributes significantly to the total water volume in Alaska’s waterways. Generally, flow rates are the highest during spring snowmelt, but this higher flow is associated with significant debris flowing within the water channel. Debris is often directed to the fastest area of flow (the thalwag) and is not necessarily confined to the surface. In the winter, river flow often drops off dramatically and is largely supplied by local groundwater. This fact coupled with challenges associated with ice/turbine interactions leaves open to question whether hydrokinetic devices would be cost effective during winter months in most Alaskan rivers. If hydrokinetic devices are only deployed seasonally in riverine environments, an imbalance between resource availability and electricity demand (which is often highest in the winter months) will result.
It is possible that in dealing with resource and load fluctuations on short time periods, energy storage could be utilized or excess energy could be dissipated for heating purposes (see the Energy Storage section for more information).
The hydrokinetic working group agreed that commercial projects will likely be operating in the state in the next three to five years. The group was not ready to make specific recommendations (see below) for hydrokinetic projects for specific villages in Alaska. Recommendations from the working group are less project specific. They are tipped toward finding appropriate ways to move forward with this technology. The members of the working group stressed that its success is tied to not overestimating the maturity level of the technology by skipping over beta testing and demonstration phases.
Hydrokinetic energy represents a real opportunity for power generation using local resources at select locations in Alaska; however, there are still numerous environmental and technical challenges associated with this technology. For example, there are concerns related to interactions between turbines and both adult and juvenile fish, since most communities with hydrokinetic resources are heavily dependent on local subsistence and commercial fisheries. Additional concerns include ice interaction with infrastructure, silt abrasion, submerged debris which could damage turbines, navigation hazards, and impacts on marine life.
The actual construction and operation of a pilot device or devices will result in a more complete understanding of technical, environmental, and cost factors associated with hydrokinetic energy. This would provide a solid starting point for additional cost and economic analysis for specific sites around the state.
|TECHNOLOGY SNAPSHOT: HYDROKINETIC|
|Installed Capacity (Worldwide)||1500 kW worldwide, all demonstration projects|
|Installed Capacity (Alaska)||0 kW installed|
|Number of communities impacted||Potentially available to communities in all regions of Alaska located near a major waterway or tidal basin, excluding the North Slope|
|Technology Readiness||Pre-commercial to early commercial|
|Environmental Impact||Impacts on local hydrology and aquatic species must be assessed on a case by case basis. AEA anticipates that these impacts can be minimized by appropriate siting, design and operation.|
|Economic Status||A 2008 EPRI study calculates paybacks in the 3-9 year range for three proposed hydrokinetic sites in Alaska, however this has not been verified by a commercial installation.|
|Case Studies||Igiugig In-River Hydrokinetic Site, Cairn Point at Knik Arm Tidal Energy Site, Nenana, Eagle|
Alaska Specific Technology Challenges
|• Environmental concerns, especially with regard to impacts on fish must be addressed. Fishery resources in Alaska have unparalleled value for subsistence, sport, and commercial use. It is critical that hydrokinetic energy development be fully evaluated for impacts on these resources.||• Survivability and performance issues must be examined. Alaskan waters have many hazards for hydrokinetic devices, including high rates of sediment transfer in river beds, debris, and ice. These issues also complicate the design of anchoring and cabling systems.|
|• Resource assessment is necessary. There is a shortage of river velocity and depth data, particularly for winter months.||• Effects on navigation are important. Many of the fast flowing rivers in Alaska with potential for hydrokinetic development are also major waterways for barge delivery of bulk materials to isolated communities. A major consideration is that these devices not impede river traffic.|
Cook Inlet – In 2008, Ocean Renewable Power Company, LLC obtained a FERC initial permit and the company is in the process of applying for a pilot project license to begin development of a demonstration tidal project near Fire Island that will connect to the Fire Island intertie. The site could ultimately yield an estimated 17 MW of power, enough to power 17,000 homes. ORPC intends to install the project in a phased approach with the first devices being deployed in Cook Inlet in 2012.
Gastineau Channel – The FERC permitting process has begun for a demonstration project in Gastineau Channel, which could ultimately provide up to 24 MW of electricity generation to supplement Juneau’s already existing hydropower sources.
Nenana – Ocean Renewable Power Company and Alaska Center for Energy and Power have preliminary permits to establish a hydrokinetic testing site in the Tanana River near Nenana. The site will provide testing grounds for a variety of hydrokinetic devices, with the first scheduled to be in the water by summer 2010. The pilot project license application was submitted in Fall 2009.
Links and Resources
Below are the specific recommendations that came out of the hydrokinetic technology working group include:
- Develop guidelines and protocols on how to initiate projects.
- Develop methods to prioritize potential projects.
- Conduct additional site-specific resource assessment in Alaska, including screening of locations with a list of compatibility factors, to determine optimal sites. This is necessary for project development and does not commit the state to failure by deploying technology too soon.
- Quantify and streamline permitting requirements, and draft a recommendation to have the state review FERC licenses. Encourage communities to protect their own interests by applying for site permits near their locations.
- Conduct more research as needed in terms of impacts on fish populations.
- Involve the University of Alaska as an independent source for device testing.
- Support demonstration and pilot scale projects to come up with defensible numbers (projections) for future project costs. Get data on how devices are working and how manufacturers can improve and modify devices. Optimize technology for Alaskan environments.
- Support development of a coordinated national research program to avoid multiple small failures in disparate locations. Position Alaska (possibly through the University) to take a leading role. Such a test center could also serve to promote cross-fertilization and standardization of ancillary equipment, such as development of a universal platform for installation of turbines, including a deployment strategy.
Alan Fetters, Bob Grimm, Brian Hirsch, Dale Smith, David Lockard, David Oliver, Dennis Witmer, Doug Johnson, Eric Munday, Gwen Holdmann, James Lima, Jan Konigsberg, JC Barger, Jim Ferguson, Jim Norman, Lena Perkins, Lenny Landis, Monty Worthington, Phil Brna- FWS, Rebekah Luhrs, Robert Thomas, Scott Newlun, Stan Lefton, Steve Gilbert, Steve Selvaggio, Tiel Smith, and Walter R. Dinkins
- Alaska Hydrokinetic Energy Research Center (AHERC). From the website: "[AHERC] focuses on applied research and engineering specifically related to extracting power from the kinetic energy of moving water in rivers and tidal basins. AHERC conducts environmental and technical studies that benefit a broad cross-section of developers. Such topics include fish and marine mammal baseline studies of interest to permitting agencies, approaches to anchoring and debris mitigation, the prevalence of turbulence and its effects, and other problems common to the Alaskan hydrokinetic power generation efforts."
- Alaska Hydrokinetic Working Group. From the website: "Goals: 1) Promote collaboration between industry, university researchers, and state and federal agencies. 2) Provide forum to discuss and evaluate needed environmental studies and research methods. 3) Define clear objectives for technical and engineering studies."
- Ocean Renewable Power Company, LLC., Alaska Projects. Information on ORPC's hydrokinetic projects in Alaska.
- DOE EERE's Marine and Hydrokinetic Technology Database. Contains information on marine and hydrokinetic renewable energy in the U.S. and around the world.
- **In-River Systems: A link to the Alaska Renewable Energy website. A great source to learn about upcoming renewable energy projects in Alaska.
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