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Renewable Energy from the Ocean
North Carolina’s Coastal Conference
Billy L. Edge
North Carolina State University – CCEE
UNC-Coastal Studies Institute
14 April 2015
Why pursue renewable ocean energy?
There are substantial global resources available
Energy (TWh)
Source
20,205
U.S. Energy Information Administration (2010) International Energy Statistics.
http://www.eia.gov
32,000
Mørk, G, Barstow, S., Pontes, M. T, Kabuth, A., (2010). Assessing the Global
Wave Energy Potential, submitted to OMAE 2010, Shanghai, China, 2-6 June
2010.
Theoretical global tidal
range resources
7,800
Estefen, S. (2012). Ocean Energy in View of the IPCC Report with an Emphasis
on Brazilian Activities. Thirteenth Meeting of the United Nations Open-Ended
Informal Consultative Process on Ocean and the Lawn of the Sea.
Theoretical global ocean
current resources
5,000
Global electricity
demand (2011)
Theoretical global wave
resources
Outline
1. Legislative Mission
2. MHK
3. Strategic Research Directions
4. 30-Year Wave Hindcast
5. Summary
Legislation
Mission
Use renewable ocean energy wisely to effectively and
economically fulfill part of the energy needs of North
Carolina and in the process create jobs and economic
opportunities.
UNC Coastal Studies Institute
North Carolina State University
UNC Charlotte
NC A&T
UNC – IMS
UNC – Chapel Hill
Renaissance Computing Institute
RME, SEMREC, Verdant, TAMU, Johns Hopkins
Renewable ocean energy?
Renewable energy available in the waters
of Earth’s oceans:
• Ocean Thermal Energy Conversion (OTEC) temperature differences between warm surface waters
and cold deep waters
• Salinity Gradient - differences in salinity
concentrations between fresh waters and the saline
water that they run in to
• Marine Hydrokinetic Energy (MHK) movement of water in waves, tidal currents, and ocean
currents
Wave energy device technologies
Attenuator
Surge converter
Point absorber
Oscillating water column
Bulge
Overtopping terminator
Submerged pressure
differential
Rotating mass
Animation source: http://www.emec.org.uk/marine-energy/
Ocean Power Technologies - PowerBuoy
Source: http://www.oceanpowertechnologies.com/tech.htm
PowerBuoy® 40 kilowatt
Utility scale, Grid Compatible
Wave Energy Resource
 Objective
 Develop high resolution 30 year hindcast
 Estimate extreme wave conditions
 Provide results in GIS and HTML framework
 Rationale
 Information to attract developers
 Requires high resolution NC data
 ADCIRC-UnSwan
Courtesy: CORPS, NCSU, CSI & RENCI
Wave Energy (1999 Floyd)
ADCIRC+SWAN
Current energy device technologies
Oscillating hydrofoil
Horizontal axis turbine
Archimedes screw
Enclosed Venturi tips
Vertical axis turbine
Tidal kite
Animation source: http://www.emec.org.uk/marine-energy/
Tidal Energy
Strategic Directions
1. Magnetic Gears for PTO
2. Ocean Compressed Air Energy Storage
3. Environmental, Regulatory and Environmental
Assessment
4. Gulf Stream Power
 Support for Jennette’s Pier Research
 Special Projects
Drawbacks of Mechanical Gears for Marine
Hydrokinetic Power Generation
• Reliability (physical contact between gears)
• Requires lubrication and maintenance
• Vibration and acoustic noise
• No overload protection
• Failures are often catastrophic
• Short operating life time
13
A Flux Focusing Magnetic Gearbox
• Magnet’s field directed along angular direction
• Approach increases the field within the air-gap
2-D model of a flux focusing magnetic gear with p1=4 pole-pairs, n2=17 steel
poles and p3=13 pole-pairs on outer cylinder. 1:4.25 gear ratio.
Experimental
Testing
Stationary outer rotor
Inner rotor
Cage rotor
Torque transducer
on high speed end
3-phase generator
on high speed end
Magnetic gear
box
Torque
transducer on low 3-phase motor on
low speed end
speed end
15
Intermittent power to meet baseload
using storage
Daily wave power
generated
Excess To
storage
From storage
Daily electricity
demand
Storage: Compressed Air Energy Storage (CAES)
Ocean Compressed Air Energy Storage
Courtesy: Dr. Mohammad Gabr, NCSU
OCAES SYSTEM – OIL/GAS SUBSEA
Subsea Reservoir
Air Lines and
Subsea Valves
Power Island
Proprietary and Subject to the Terms of the Nondisclosure Agreement
Capacity Building: Environmental and
Stakeholder Assessment
Challenge:
 Many users of the coastal ocean, by
humans and other organisms
 Protected species, habitats, and
cultural resources in the coastal ocean
Solution:
 Examine the spatial extent of
potential conflicts
 Identify potential conflicts and
synergies in the coastal ocean
Outcomes
 Conflicts were mapped for future
siting purposes
 Potential conflicts and synergies were
identified for future study
Research team: Lindsay Dubbs, UNC-Chapel Hill and UNC
CSI; Michael Piehler,
Assessing the effects of Gulf
Stream turbines on Sargassum
communities
Lindsay Dubbs and Michael Piehler

Sargassum fluitans and natens comprise an important
floating pelagic ecosystem entrained in the Gulf
Stream. Sargassum is important to the ecology of the
Atlantic Ocean because:

Many organisms live on or within clumps and mats

Shelter is provided below the macroalgae and food is
provided from above and below Sargassum and its epibionts

cycle nutrients – carbon uptake and nitrogen fixation
30 50 m
How is Sargassum related to Gulf Stream energy?
Sargassum floats at the water’s surface and Gulf Stream turbines will likely be located at depths of 30-50 m below
the water’s surface. Nonetheless, wakes generated by turbines may effect Sargassum communities.
Research questions:
1.
What is the spatial and temporal distribution and general structure of Sargassum communities along the
western wall of the Gulf Stream off the coast of Cape Hatteras, North Carolina?
2.
How do changes in hydrodynamic forces affect productivity, nitrogen fixation, and respiration of Sargassum
and its epibionts?
The Gulf Stream
• Average Gulf Stream shown in
white dashed lines
• COLDER blue water, WARMER
red & orange water
• Gulf Stream red & orange
slide courtesy of Caroline Lowcher
“Movie” of The
Gulf Stream
Gulf Stream
off NC
• 15 – 20 Nautical
Miles
NC
15-20NM
• Current speeds
in excess of 2m/s
• 90 Sv (106 m3/s)
volume
transport
• Steep shelf slope
Use Radar Surface Currents to locate the
Gulf Stream Edge
Before Core Radar
After Core Radar
Vel cm/s
100
NC
NC
50
Core Radar
ADCP Measurements
ADCP Measurements
0
Observations
1. 150 kHz ADCP Mooring
• Long term
• Entire water column
• One location
• 8/01/2013 - now
DUCK
radar
NC
HATY
radar
CORE
radar
*
150 kHz ADCP mooring
Moored ADCP Along Stream Currents
at water depth 228m
Height Above Bottom
200 m
3 m/s
0 m/s
20 m
-3 m/s
Aug. 2013
9 Months
May 2014
MAB-SAB Model Configuration
Ocean Depth
Based on the Regional Ocean
Model System (ROMS)
2 km spatial resolution, 36 terrain
following vertical layers
study focus region
Boundary conditions are from
global data assimilative HYCOM
model
35 km spatial and 3 hourly
temporal resolution NCEP North
America Regional Reanalysis
(NARR) atmospheric forcing
15 major rivers and M2 tide
Hindcast periods: 2004-2005;
2009-2014
(Gong, He, Gawarkiewicz and Savidge, 2014)
Potential Turbine Site
75m over 225m isobath
Conclusions
 Significant Amounts of Renewable Energy in the Ocean
 Cost of devices and operation must be reduced to be
competitive
 Ocean environment is a highly dynamic place to model and to
operate
 GPUSPH with embedded Open Dynamics Engine allows for
modeling of wave energy devices.
ATHOS Consortium