Introduction
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.
Alaska’s first in-stream hydrokinetic turbine, located in Ruby
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.
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.
EETG: Yukon Hydrokinetic Project
EETG: Nenana Hydrokinetic Turbine
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 Technology
| 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 |
For more information on hydrokinetic technology, click on the link below:
HYDROKINETIC TECHNOLOGY
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Links and Resources
- 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.
