OCEAN CURRENT ENERGY Ocean Currents, Available Technology, & Economic Feasibility
BY: MATTHEW SAVIN
[email protected]
Hydrokinetic vs. Hydropower To understand ocean current energy, the distinction between hydropower and hydrokinetic power must be understood
“Hydropower” Alters the environment to create useable energy from rivers and streams
“Hydrokinetic” Harnesses the existing flow, current or velocity of water without altering the environment
Two Examples of Hydrokinetic Power 1. Tidal Power: Technology that attempts to harness the energy that is created from waves
2. Ocean Current Power: Technology that attempts to harness energy from ocean currents and streams
Although both use similar technology, we will focus mainly on “Ocean Current Power”
What Are Ocean Currents? Surface Currents:
328 Ft. (100 meters) or above Coastal Currents Surface Ocean Currents Development of ocean current energy technology refers to the use of “surface currents”
Deep Ocean Currents (Global Conveyer Belt) For our purposes, we will focus solely on “surface currents”
What Drives Surface Ocean Currents? The Coriolis Force: Wind is the primary factor in forming Surface Ocean Currents The earth’s spin causes winds to curve right in the northern hemisphere, and left in the southern hemisphere (Coriolis Force) Thus, in the northern hemisphere, wind from the west pushes warm waters north, and wind from the east pushes cold water south Gyres: the circular pattern that develops from the combination of westerly and easterly wind
5 Major Gyres
Other Factors… In addition to wind & the Coriolis Force, several other factors contribute to surface ocean: currents Thermohaline Circulation: Temperature (Solar Heat) Water Salinity (Density) Tidal Currents: Earth’s gravitational pull
Ocean Current Energy Potential Ocean currents travel at speeds significantly slower than wind
However, water is 800 times as dense as air
Thus, a 12 mph ocean current would have an energy output equal or greater to a 112 mph wind
By some estimates, 1/1000 of the energy of the Gulf Stream could satisfy 35% of Florida’s energy needs
Characteristics of Ideal Ocean Current Candidates: 1.
Strong Current: Some claim that a mere 1 knot current could produce substantial
2.
energy However, most approximates say that only 4-5 knot current could produce enough energy to justify the expenditure
Shallow Water Depth
Available technologies (based on wind & tidal prototypes) have only proven effective at relatively shallow depths Other issues – such as access to equipment for maintenance – limit ocean current facilities to shallow depths
3.
Close Proximity to Shore:
Because transmission lines are needed to transport the energy generated to the onshore grid
Where Are Ocean Currents Located? In addition to the US, the UK, Ireland, Italy, Philippines, and Japan have access to potentially useable ocean currents
Three Major Currents in the United States: 1. The Gulf Stream 2. The Florida Straits Current 3. The California Current
The Gulf Stream & Florida Straits
The California Current
Advantages of Ocean Current Energy Energy Density One obvious benefit of ocean current energy is that its energy density is far superior to wind, using similar to identical technology.
Reliable/Constant Energy Output Unlike wind and solar, an effect ocean current would remain relatively constant Thus, unlike wind, utility companies could safely purchase its energy output at a level near the generating facility’s capacity
No GHG Emissions Minimal Environmental Alterations
How Would Ocean Current Technology Work? Three basic features: 1. Rotor Blades 2. A Generator 3. Transmission Lines (for bringing electricity to an onshore grid)
Two Potential Designs: 1. Submerged Water Turbines 2. Parachutes
Submerged Water Turbines The most common prototype would essentially operate in the same way as a wind turbine
The turbine would be fastened to the ocean floor, with water pushing the turbine instead of wind
Two Types of Submerged Water Turbines: 1. Vertical 2. Horizontal
Horizontal Submerged Turbines Most people are already familiar with the general design of a horizontal submerged water turbine
It would resemble & operate like a traditional windmill
The turbines would have an axis of rotation horizontal to the ground
Vertical Submerged Water Turbines Vertical turbines (the design on the right) operate similarly to horizontal turbines
However, the axis of rotation would be vertical to the ground
“Parachutes” Another prototype would fasten a cable to the ground, allowing the turbine to float above
This design would operate much like a person flying a kite
However, there would be a series of kites that would continuously rotate, opening to harness the current, and closing on the return trip
Parachute vs. Waterwheel
Parachutes Cont’d
Fastening to the Ocean Floor Exactly how the turbines would be fastened remains to be seen
However, most prototypes have borrowed ideas from either offshore windmills or offshore oil rigs
Given the similarities, the same technology should work with ocean current energy…
Fixed-Bottom Substructure Technology 1.
Monopile Foundation:
Minimal Footprint Depth Limit = 25 meters Low Stiffness
2.
Gravity Foundation:
Larger Footprint Depth Limit = Unknown Stiffer, but more stability
3.
Tripod/Truss Foundation:
No Testing for Turbines (Wind or Submerged) Yet… Oil/Gas Depth of about 450 meters Larger footprint
3 Basic Design…
Technical Challenges Avoiding Cavitations: Bubbles on the rotator blades may create resistance that can reduce efficiency
Marine Growth Buildup: Will need to be managed to ensure that interference with the equipment is minimal
Reliability: Maintenance costs are typically high, which means the equipment must be relatively reliable to avoid constant replacements and diving expeditions
Corrosion: Given the expense of equipment & maintenance, measures need to be taken to ensure that the equipment doesn’t corrode from underwater elements
Can We Overcome Technical Challenges? While the technical and environmental concerns are daunting, there is hope…
Innovations from the private sector have offered promising designs
The federal government has also shown a renewed interest in both hydropower & hydrokinetic projects…
Alternative Designs Given the technical difficulties resulting from of underwater corrosion, maintenance difficulties, and stability concerns, the private sector has developed some innovative alternative designs...
But the practicability and expense of these designs remains relatively unknown, as most are in the preliminary stages…
EXAMPLE 1: Hydro Green Energy Instead of fastening the turbines to the ocean floor, one such design relies upon a floating base
The turbines are connected to the flotation device on the water surface, essentially operating as an upside down horizontal turbine
There are numerous advantages to this design, including: No alteration of the ocean floor Easy maintenance, as the turbines can be replaced by simply removing/replacing them above water Presumably, lower infrastructure costs
Hydro Green Prototype… Hydrogreen’s Prototype places the turbines just below the surface, attaching them to a floating foundation
This could alleviate some of the maintenance and foundation problems…
Hydro Green Cont’d Could replace each turbine without entering the water
No need to fasten the turbines to the ocean floor, which eliminates foundation expenses and design uncertainty
What About Environmental Concerns? Species Protection: Shipping Route Interference Recreational Uses
Slowing the Current Flow Changes in Estuary Mixing
Potential Environmental Solutions… Species Protection? Slow Blade Velocity Protective Fences Sonar Brakes Shipping/Fishing? Fishery Exclusion Zones Slowing Current? Unknown Estuary Mixing? Unknown Conclusion: Large-Scale Testing Necessary
Economic Considerations Infrastructure: Unfortunately, the initial cost of ocean current technology would be expensive Transmission Lines
Government Funding: Infrastructure Subsidies
Energy Output & Consumer Pricing Energy Output Maintenance Costs
Open Market or Monopoly?
Transmission Lines The single largest expenditure will relate to construction of the initial infrastructure
Setting up transmission lines will be the most expensive and challenging, as underwater lines will be necessary
While the initial expenditure would be great, its effect on the consumer would be marginal in the long-term, as the only costs would relate to maintenance
Google Wind Farm However, if projects such as Google’s wind farm materialize, then transmission lines might be available for hydrokinetic power as well
Government Funding & Department of Energy… In September of 2010, the DOE provided $37 million towards harnessing energy from US waterways, the largest such grant yet…
While estimates for the initial infrastructure costs are in the billions, there appears to be growing interest in ocean current and tidal energy
Federal or State Funding? How much of the financial burden should States assume?
Regional Partnerships?
Is this a project that only the federal government can implement?
Should taxpayers in the Midwest have to pay for energy being developed on the coast?
Government Regulation: Open Market or Monopoly? Another variable is to what extent economic factors would be left to market forces
This would depend in large part upon whether the infrastructure would allow competition among electricity distributors for the generated energy
Increased competition among distributors could lower the cost to the consumer, although federal regulation would probably be necessary to avoid “gaming the system”
Who Will Regulate? Which Agency? DOE? FERC?
Federal vs. State? How much state control? Regional Development?
Cost to the Consumer? Two variables will influence the eventual cost to the consumer: energy output & maintenance costs
ENERGY OUTPUT: because large-scale testing and development have yet to materialize, the actual energy output that could be utilized remains unknown
MAINTENANCE: in addition, until large-scale testing and development is implemented, the cost of maintaining the facility remains unknown, which would be passed on to the consumer
Consumer Cost Cont’d… The ultimate cost to the consumer will depend upon the supply of energy that each generator is able produce
Greater Energy Output = Greater Supply = Lower Consumer Cost
SUMMARY Technical Challenges
Large-scale testing is necessary to determine how much maintenance will be involved with each prototype
Environmental Concerns
The most significant concern is the slowing of the ocean current itself, which requires large-scale testing as well
Economic Feasibility?
Will depend upon both the maintenance costs and the energy output Government funding will also be necessary
Government Regulation:
It remains unknown which agency, and to what extent, the government will regulate the offshore facilities
CONCLUSION: WE NEED LARGE-SCALE TESTING, BUT THERE IS HOPE FOR OCEAN CURRENT ENERGY!!
