Ocean-Current Power Generation for Florida
A Position Paper by the Big Bend Climate Action Team
Tallahassee, Florida, September 2007
The Big Bend Climate Action Team recommends that Florida invest its available resources, time, human creativitiy and effort in the following areas to reduce the negative effects of climate change:
First, establish policies to implement conservation and energy-efficiency measures.
Second, take advantage of clean, non-fossil, renewable resources to meet increasing demand.
Ocean energy is one promising renewable resource that might be tapped to meet Florida’s needs for electric power. This paper discusses several renewable ocean-energy resources available to Florida and focuses in detail on the most likely one, ocean-current power generation. Much of the information presented here has been taken directly from a research paper published in May of 2006 by the Minerals Management Service, which provides a concise but thorough picture of ocean-current power generation potential.(1)
Background Information
Governor Charlie Crist is leading Florida into the forefront of the nation’s efforts to curb global warming. In March he announced his intention to make Florida a leader in energy efficiency and renewable technologies and in July he hosted an in-state Climate Change Summit. Under his leadership, Florida has signed climate-change initiatives with California and with the northeastern states and international partnership agreements with the United Kingdom and Germany. The governor has issued three executive orders directed at changes in policies and procedures to mitigate the negative impacts of global warming. He has called global climate change “one of the most important issues (that faces) the State of Florida this century.”
Florida is poised to proactively engage in measures to curtail energy needs and reduce reliance on fossil fuels. A 2007 study by the American Council for an Energy-Efficient Economy (ACEEE) shows that a combination of energy efficiency and renewable energy can reduce florida’s future electricity needs by almost half (45%) over the next 15 years.
Forms of Ocean Energy
The various forms of ocean energy are ocean thermal energy, wave energy, tidal energy, and ocean currents.(2) The three that involve hydraulic energy—waves, tides, and currents—are discussed in this paper. Maps below show where energy is most needed due to the world’s population distribution and where ocean energy resources are most readily available around the world.
Figure 1 shows the lights radiating at night from human population centers as seen from space. The lightest areas indicate which areas of the world are currently demanding the greatest amounts of energy. Clearly, Florida, being brightly lit up at night, is one of those areas.
Figure 1. Earth at night, 27 November 2000
Source: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive
Waves. Figure 2 shows average wave energy potential worldwide, expressed in kilowatts per meter of wave front. It is apparent that wave energy availability and energy need are not necessarily juxtaposed. Florida’s rank in standing for wave energy is in the low range of potential for this resource.
Figure 2. World-wide average ocean wave-power energy potential
Source: Wave Energy paper. IMechE, 1991 and European Directory of Renewable Energy (Suppliers and Services) 1991 © 2005, Trident Energy Limited
Tides. Figure 3 shows the areas around the world that have the best potential for energy from tides. Generally, on a large scale, areas with the greatest differences between high tide and low tide have the best potential. On a smaller scale, seabed contours play an important role in generating tidal currents and in their strength. As with wave energy, Florida fairs poorly when tidal energy is evaluated as a possible source of electrical power generation.
Figure 3. World-wide locations where ocean tidal currents are viable energy sources
Source: Statkraft Development AS, Olso, February 2006, Tidal power: Versatile, Reliable, Renewable
Currents. Figure 4 shows the world’s ocean currents (red arrows indicate warm currents, blue arrows indicate cold currents). Not all are well suited to provide energy where it is most needed. However, along Florida's east coast, energy needs and this renewable energy resource are in alignment.
Figure 4. The world’s ocean currents
Source: PhysicalGeography.net
Ocean-Current Resource Potential and Viability for Florida
Whereas Florida seems unsuited to make use of the ocean’s wave and tide energy, the state is strategically located to take advantage of two of the world’s most consistent ocean currents, the Florida Straits Current and its continuation, the Gulf Stream, shown in Figure 5. The Florida Straits Current starts only 8 km offshore in the southern part of Florida, close to Miami, and sustains relatively constant speeds over significant distances in relatively unchanging patterns. Ocean currents’ fastest velocities tend to be concentrated at the surface, although significant current continues at depths below ships’ drafts.
Figure 5. The Florida Straits Current and the Start of the Gulf Stream
Source: Adapted from website of the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), http://oceancurrents.rsmas.miami.edu/atlantic/florida.html
An advantage of most ocean currents is that they are relatively constant and flow in one direction in contrast to tidal currents, which typically reverse direction diurnally. Moreover, in the case of the Florida Straits Current and the Gulf Stream, the rates of flow are favorable. For ocean currents, initial studies suggest that velocities of at least 2 meters per second (4 knots) are required for economic exploitation. It is possible, however, to generate energy from velocities as low as 1 meter per second. The currents by Florida usually move at a velocity of from 1 to 2 meters per second.
Ocean current velocities are considerably slower than wind velocities. This is significant in relation to their usefulness for electricity generation, because the kinetic energy contained in flowing bodies is proportional to the cube of their velocity. However, a more important factor determining the power available for extraction from a flowing body is the density of the material: water is about 835 times denser than wind. Thus, for example, a 5-knot current has the kinetic energy equivalent of wind at more than 100 miles per hour. Thus, ocean currents are potentially a very significant energy resource.
The amount of electrical energy that can be extracted from near the surface of the Florida Straits Current is estimated at about one kilowatt per square meter of flow area. It is further estimated that all of Florida’s energy needs could be met by capturing just three thousandths of the energy available from the Gulf Stream, which has 21,000 times more energy than Niagara Falls and a flow of water that is 50 times the total flow of all the world’s freshwater rivers.
Ocean Current Technologies
Technologies to capture ocean current energy, although developing fast, are at an early stage, and only a few prototypes and demonstration units have yet been tested. One promising approach involves submerged turbines. These are similar in function to wind turbines. They have rotor blades, generators for converting rotational energy into electricity, and transmission lines to carry the energy to the onshore grid. Posts, cables, anchors, or the like are required to keep the turbines stationary relative to the currents with which they interact. Prototype horizontal-axis turbines, similar to wind turbines, intersect the long-shore flow of current and several have been built and tested. One type of vertical-axis turbine has been tested in the Kurushima Straits off Japan.(3) Figure 6 shows examples of turbines used to generate electricity from tidal currents on the outer continental shelf which may be applicable to ocean currents as well; the one on the top right has a horizontal axis.
Figure 6. Examples of in-stream tidal technologies for use on the outer continental shelf
Sources: Hammerfest Strom AS 2006; Gulfstream Energy Incorporated 2006 (top two); National Renewable Energy Lab 6 June 2006 Michael C. Robinson, Ph.D. (bottom six).
Turbines may be anchored to the ocean floor in a variety of ways. One approach is to tether them with cables, using the relatively constant current to maintain location and stability. This is somewhat like flying a kite in the wind: the kite is the turbine, the wind stabilizes the kite, and the person is the anchor. In addition, concentrators (or shrouds) may be placed around the blades to increase the water flow through, and the power output from, the turbine.
In large areas with powerful currents, water turbines may be installed in groups or clusters to create a “marine current facility,” similar in design to wind turbine facilities. These clusters would resemble wind farms—but under water. Turbine spacing would be determined based on wake interactions and maintenance needs. A 30-megawatt demonstration array of vertical-axis turbines in a tidal fence is being investigated in the Philippines.(4)
Technical Challenges to Utilizing Ocean-Currents for Power Generation
Before marine current energy can be fully utilized, a number of technical challenges must be overcome. One is drag from cavitations—that is, air bubble formation that creates turbulence and substantially reduces the efficiency of current-energy harvest. Others are marine growth buildup, corrosion, and a lack of overall system reliability. Researchers are currently conducting studies to overcome these issues. The logistics of rotor and turbine maintenance have been shown to be more complex than with land-based wind rotors and turbines, resulting in higher operating costs. However, as experience is gained working in an aqueous environment, developers may be able to overcome these challenges and succeed in making this potential base-load source of electrical energy reliable.
Transmission of electricity from energy sources on the outer continental shelf to an onshore location will require submarine cables. No currently operating commercial ocean-current turbines are connected via cable to electric-power transmission lines or distribution grids. However, submarine cable technology is presently being used to transmit electricity from offshore wind facilities to onshore electric power substations in Europe; while in the United States, a number of ocean-current turbine configurations are being tested on a small scale. For example, in the year 2000, three companies received small business innovation research (SBIR) awards from the U.S. Department of Energy to explore ocean-current power generators. An earlier study of ocean-current energy extraction from the Florida Straits Current, performed in the 1980s, used modeling to explore possible configurations and environmental effects.(5) At present, eight ocean current projects are underway off Florida’s east coast in the Florida Straits Current and the Gulf Stream (see later section on Florida projects). High-voltage alternating-current (HVAC) electric transmission lines are typically used where economically justified by distances of 30 to 250 kilometers. The proximity of suitable ocean current velocities located between 3 and 15 miles of Florida’s east coast would pose few if any unusual obstacles to setting up HVAC transmission lines.
Environmental Considerations Relating to Ocean-Current Power Generation
Potential environmental impacts from the development and utilization of ocean current energy on the outer continental shelf include impacts on marine ecology and conflicts with other potential uses of the same ocean areas. Resource requirements associated with the construction and operation of ocean-current technologies also need to be addressed. Regardless of the magnitude and nature of anticipated environmental impacts, project planning must consider the protection of species, particularly fish and marine mammals.
Ocean turbines have slow blade velocities, which should allow water and fish to flow freely and safely through them. Protective fences and sonar-activated brakes could prevent larger marine mammals from being harmed. Assurance that current-power modules won’t endanger marine life needs to be established; no empirical information is yet available on this point because the modules presently being tested are the first of their kind, but the Ocean Renewable Power Company-Maine (ORPC) claims that the slow revolution speed of the blades will not endanger marine life and that sonar-detection systems can detect and regulate rotor speed to protect any large marine life that might be threatened.
Other considerations important in the siting of the turbines are impacts on shipping routes, and present as well as anticipated uses such as commercial and recreational fishing and recreational diving. There may also be a need to introduce possible mitigating factors, such as the establishment of fishery exclusion zones.
Concerns have been raised about the slowing of current flows by extracting energy from them. Changes might be caused in the temperature and salinity of nearby estuaries. These potential impacts need to be further studied.(6)
Current and Proposed Florida Hydropower Facilities
Ocean current power facilities are a subset of hydropower facilities, which are receiving a generous share of today’s increased interest in renewable energy. In the three years between 2004 and 2007, U.S. energy regulators received nearly five dozen applications for water-related energy projects from South Florida to the State of Washington.(7) Currently, there is only one licensed and operating hydroelectric power plant in Florida; its energy is derived from a dam on the Ochlockonee River located west of Tallahassee. A permit has been issued for another conventional hydroelectric power facility on the Withlacoochee River that is projected to generate an annual average of 12.3 gigawatt hours.
Eight hydroelectric power project permits have been issued to applicants exploring the future possibility of licensing ocean-current power facilities using the Florida Straits Currents and the Gulf Stream. Facilities are to be installed offshore near the following locations: Palm Beach County, Fort Lauderdale, Key Largo, Miami, Sebastian, St. Lucie, Tavernier, and West Palm Beach. These exploratory projects seek to generate between 2 and 20 megawatts of electrical energy from their prototype demonstrations of the technology.(8)
The Palm Beach project is to consist of: (1) a generation farm containing 8 submerged two-counter rotating fiberglass blades and integrated turbine generating units having a total installed capacity of 2 to 3 megawatts; (2) a proposed 3-mile-long, sub-marine transmission line; and (3) appurtenant facilities. The project is to generate 17.52 gigawatt hours annually, and this energy is to be sold to a local utility.
The Fort Lauderdale, Key Largo, Miami, Sebastian, St. Lucie, Tavernier, and West Palm Beach projects are each to consist of: (1) a generation farm containing 20 to 40 submerged SeaGen twin rotor machine generating units having a total installed capacity of 20 to 40 megawatts; (2) a proposed 25 to 30-mile-long, 33 kilovolt transmission line; and (3) appurtenant facilities. Each of these facilities is projected to generate 168 to 336 gigawatt hours annually, and this energy is to be sold to a local utility.(9)
Several Florida entities are joining forces to promote ocean-current power generation, led by Florida Atlantic University (FAU). Fredric Driscoll, Director of FAU’s Center of Excellence in Ocean Energy Technology, says that Florida is ideally situated to tap into both major sources of ocean power: mechanical and thermal. Partners in this enterprise are associates from the Florida Solar Energy Center at the University of Central Florida and associates from the Center for Advanced Power Systems at Florida State University. This task force intends to work to educate Congress and compete for a pot of $50 million being set aside in legislation to support ocean energy research projects over the next 10 years. In addition, the universities are seeking about $12 million in federal grants over the next three years from the Department of Energy, the Department of Defense and the National Oceanic and Atmospheric Administration
For the near future a well-suited candidate for an “ocean park” for the generation of power is the Miami coast. The region has a steep continental shelf with strong currents not very far from the coast (the 500-meter depth contour line is less than 30 kilometers from the coast). This short distance would help to lower the cost of maintenance and power transmission losses. For this area, the combination of wind and ocean currents would provide sustainable and clean resources for present and future generations, perhaps using shared underwater transmission lines.
Summary and Conclusion
The Big Bend Climate Action Team strongly endorses the use of renewable energy resources to the greatest extent possible for meeting Florida’s future energy needs. A study conducted by the Florida PIRG Education Fund in 2005 demonstrated that many economic and public benefits can accrue from the use of renewable sources of energy for the state in regard to jobs, gross product value, reduced electricity bills, and reduced global-warming carbon-dioxide emissions from power plants.
Moreover, the Big Bend Climate Action Team considers ocean-current power to be a promising renewable energy technology for our State, given our natural ocean current resource. The high current velocities which occur within parts of the Gulf Stream off the east coast of Florida provide easy access to an abundance of energy derived from consistent ocean currents. Further, it seems probable that ocean-current technologies can become more suitable for Florida than wind power. Ocean currents are steadier and more reliable than wind and can provide constant base-load energy. Given all of its other advantages, ocean-current power generation appears to be a promising, viable, clean alternative energy source. Big Bend Climate Action Team hopes that the financial investment projections will encourage further development of this technology.
Ocean-current power technologies have many favorable characteristics, including the following:
• Water currents have high energy densities.
• Ocean currents are relatively constant in location and velocity, producing a large capacity factor (fraction of time actively generating energy) for the turbines.
• Because they are installed beneath the water’s surface, water turbines have minimal visual impact and no impact on maritime vessels.
These technologies seem especially suitable for Florida in particular, because the largest ocean current energy resources on the U.S. offshore continental shelf are the Florida Straits Current and the Gulf Stream, and both flow close to Florida’s east coast from Miami to Jacksonville, coastal population centers with high power demands.
We encourage state, county, and municipal leaders to maximize conservation and energy efficiency measures, including distributed generation, cogeneration, load control, load shifting, tiered rates, and other such measures to reduce demand, and to take advantage of solar power, geothermal energy, and biomass as well as to increase ocean energy research and full-scale implementation of technologies to fully realize the benefits of this valuable resource for our State.
Specific References:
- Minerals Management Service, Renewable Energy and Alternate Use Program, Technology White Paper on Ocean Current Energy Potential on the U.S. Outer Continental Shelf, May 2007.
- The section on Ocean Energy is based largely on information on the Ocean Energy Council website: http://www.oceanenergycouncil.com/whatis.html
- World Energy Council (WEC), 2001, “2001 Survey of World Energy Resources,” http://www.worldenergy.org/wec-geis/publications/reports/ser/overview.asp
- WEC, 2001.
- National Technology Transfer Center, 2000, Phase I Awards by Topic, July 13, 2000, http://www.nttc.edu/resources/funding/awards/doe/2000/p1sbir.asp
- Charlier, R. H., and J. R. Justus, 1993, Ocean Energies: Environmental, Economic and Technological Aspects of Alternative Power Sources, Elsevier Science Publishers, Amsterdam, Netherlands.
- Adrian G. Uribarri (Los Angeles Times staff writer), Dreams of converting ocean energy into electricity move closer to commercial reality, 7:42 PM PST, 10 March 2007.
- Preliminary permits issued on 5 September 2007 are listed on the Federal Energy Regulatory Commission website, http://www.ferc.gov/industries/hydropower/gen-info/licensing/pre-permits.xls
General References:
Charlier, R. H., and J. R. Justus, 1993, Ocean Energies: Environmental, Economic and Technological Aspects of Alternative Power Sources, Elsevier Science Publishers, Amsterdam, Netherlands.
Gulfstream Energy Incorporated, 2006, “Gulf Stream Energy Project,” www.energy.gatech.edu/presentations/mhoover.pdf.
Hammerfest Strøm AS, 2006, “Proven Tech, The Blue Concept,” http://www.e-tidevannsenergi.com/.
National Technology Transfer Center, 2000, Phase I Awards by Topic, July 13, 2000, http://www.nttc.edu/resources/funding/awards/doe/2000/p1sbir.asp
University of Texas Libraries, 2006, “Perry Casteñada Library Collection,” http://www.lib.utexas.edu/maps/
World Energy Council, 2001, “2001 Survey of World Energy Resources,” http://www.worldenergy.org/wec-geis/publications/reports/ser/overview.asp
National Renewable Energy Lab, 6 June 2006, Renewable Energy Technologies for Use on the Outer Continental Shelf; Michael C. Robinson, Ph.D.
Minerals Management Service, Renewable Energy and Alternate Use Program, U.S. Department of the Interior, May 2006, Technology White Paper on Ocean Current Energy Potential on the U.S. Outer Continental Shelf, http://ocsenergy.anl.gov
Kempton, W., R. Garvine, and J. Firestone, University of Delaware, Spring 2005, MAST-667- Wind and ocean power resources off the Florida coast, USA, http://www.ocean.udel.edu/windpower/docs/PimentaRabeEtAl2005-MAST667-FINAL-V12.pdf
Lipman, Larry, 7 May 2007; Cox News Service, “Ocean Energy Moving Toward Reality, Congress Told.”
U.S. Department of Interior, Minerals Management Service, Programmatic Environmental Impact Statement for Alternative Energy Development and Production and Alternate Use of Facilities on the Outer Continental Shelf, Executive Summary and Chapter 3, Overview of Potential Alternative Energy Technologies on the Outer Continental Shelf, March, 2007 http://ocsenergy.anl.gov/documents/dpeis/index.cfm
R. N. Elliott, M. Eldridge, A. Shipley, J. Laitner, and S. Nadel, ACEEE; P. Fairey, R. Vieira, and J. Sonne; Florida Solar Energy Center; A. Silverstein, B. Hedman and K. Darrow; Energy and Environmental Analysis, Inc., “Potential for Energy Efficiency and Renewable Energy to Meet Florida's Growing Energy Demand,” June 2007, Executive Summary, http://www.aceee.org/pubs/e072.htm
The mission of the Big Bend Climate Action Team (BBCAT) is to help local governments, businesses, and citizens to do their share to abate climate change by reducing fossil fuel use and promoting energy efficiency, conservation, and renewable fuels in power plants, buildings, and vehicles
