B. S. E. E., M. S. Space Technology 15.0 Ocean Energy “It is pleasant, when the sea is high and the winds are dashing the waves about, to watch from shore the struggles of another.” Lucretius, 99-55 B.C. Frank R. Leslie, B. S. E. E., M. S. Space Technology 3/25/2004, Rev. 1.4 fleslie @fit.edu; (321) 674-7377 www.fit.edu/~fleslie

15.O Overview of Ocean Energy Ocean energy is replenished by the sun and through tidal influences of the moon and sun gravitational forces Near-surface winds induce wave action and cause wind-blown currents at about 3% of the wind speed Tides cause strong currents into and out of coastal basins and rivers Ocean surface heating by some 70% of the incoming sunlight adds to the surface water thermal energy, causing expansion and flow Wind energy is stronger over the ocean due to less drag, although technically, only seabreezes are from ocean energy 040323

15.1 Ocean Energy Sustainable energy comes from the sun or from tidal forces of the moon and sun; usually implies not using it faster than can be replenished The tidal gravitational forces and thermal storage of the ocean provide a major energy source Wave action adds to the extractable surface energy, but is less than tidal energy Major ocean currents (like the Gulf Stream) may be exploited to extract energy with underwater rotors similar to wind turbines 040324

15.1 History Some first uses of ocean energy: Tidal grain mills developed Currents used to cross the Atlantic and return Ocean winds blow boats (sometimes where desired) 040324

15.2 Sources of Energy Tidal motion of water up and down changes potential energy Changes of pressure beneath the tide height Tidal horizontal flow into basins and rivers results Wind-driven motion of water horizontally increases kinetic energy Changes in flow rate that produces strong currents Solar heating of surface waters warms the ocean by conduction Upwelling and overturning mixes and heats lower layers 040325

15.2.1 Available Energy Potential Energy: PE = mh Kinetic Energy: KE = ½ mv2 or ½ mu2 Wave energy is proportional to wave length times wave height squared (LH2)per wave length per unit of crest length A four-foot (1.2 m), ten-second wave striking a coast expends more than 35, 000 HP per mile of coast [Kotch, p. 247] Maximum Tidal Energy, E = 2HQ x 353/(778 x 3413) = 266 x 10-6 HQ kWh/yr, where H is the tidal range (ft) and Q is the tidal flow (lbs of seawater) E = 2 HQ ft-lb/lunar day (2 tides) or E = 416 x 10-4 HV kWh, where V is cubic feet of flow 040323

15.3 Ocean Energy: Tidal Energy Tides are produced by gravitational forces of the moon and sun and the Earth’s rotation Existing and possible sites: France: 1966 La Rance river estuary 240 MW station Tidal ranges of 8.5 m to 13.5 m; 10 reversible turbines England: Severn River Canada: Passamaquoddy in the Bay of Fundy (1935 attempt failed) California: high potential along the northern coast Environmental, economic, and esthetic aspects have delayed implementation Lunar/solar power is asynchronous with daily load cycle 040325

15.3 Tidal Energy Tidal mills were used in the Tenth and Eleventh Centuries in England, France, and elsewhere Millpond water was trapped at high tide by a gate (Difficult working hours for the miller; Why?) Rhode Island, USA, 18th Century, 20-ton wheel 11 ft in diameter and 26 ft wide Hamburg, Germany, 1880 “mill” pumped sewage Slade’s Mill in Chelsea, MA founded 1734, 100HP, operated until ~1980 Deben estuary, Woodbridge, Suffolk, England has been operating since 1170 (reminiscent of “the old family axe”; only had three new handles and two new heads!) Tidal mills were common in USA north of Cape Cod, where a 3 m range exists [Redfield, 1980] Brooklyn NY had tidal mill in 1636 [?] 040323

15.3 Tidal Energy (continued) Potential energy = S integral from 0 to 2H (ρgz dz), where S is basin area, H is tidal amplitude, ρ is water density, and g is gravitational constant yielding 2 S ρ gH2 Mean power is 2 S ρ gH2/tidal period; semidiurnal better Tidal Pool Arrangements Single-pool empties on ebb tide Single-pool fills on flood tide Single-pool fills and empties through turbine Two-pool ebb- and flood-tide system; two ebbs per day; alternating pool use Two-pool one-way system (high and low pools) (turbine located between pools) 040323

15.3.1 Tidal Water Turbines Current flow converted to rotary motion by tidal current Turbines placed across Rance River, France Large Savonius rotors (J. S. Savonius, 1932?) placed across channel to rotate at slow speed but creating high torque (large current meter) Horizontal rotors proposed for Gulf Stream placement off Miami, Florida 040323

15.3.1.1 Tidal Flow: Rance River, France 240 MW plant with 24, 10 MW turbines operated since 1966 Average head is 28 ft Area is approximately 8.5 square miles Flow approx, 6.64 billion cubic feet Maximum theoretical energy is 7734 million kWh/year; 6% extracted Storage pumping contributes 1.7% to energy level At neap tides, generates 80,000 kWh/day; at equinoctial spring tide, 1,450,000 kWh/day (18:1 ratio!); average ~500 million kWh/year Produces electricity cheaper than oil, coal, or nuclear plants in France 040323

15.3.1.2 Tidal Flow: Passamaquoddy, Lower Bay of Fundy, New Brunswick, Canada Proposed to be located between Maine (USA) and New Brunswick Average head is 18.1 ft Flow is approximately 70 billion cubic feet per tidal cycle Area is approximately 142 square miles About 3.5 % of theoretical maximum would be extracted Two-pool approach greatly lower maximum theoretical energy International Commission studied it 1956 through 1961 and found project uneconomic then Deferred until economic conditions change [Ref.: Harder] 040323

15.3.1.3 Other Tidal Flow Plants under Study Annapolis River, Nova Scotia: straight-flow turbines; demonstration plant was to be completed in 1983; 20 MW; tides 29 to 15 feet; Tidal Power Corp.; ~$74M Experimental site at Kislaya Guba on Barents Sea French 400 kW unit operated since 1968 Plant floated into place and sunk: dikes added to close gaps Sea of Okhotsk (former Sov. Union) under study in 1980 White Sea, Russia: 1 MW, 1969 Murmansk, Russia: 0.4 MW Kiansghsia in China 040324

15.3.1.3 Other Tidal Flow Plants under Study (continued) Severn River, Great Britain: range of 47 feet (14.5 m) calculated output of 2.4 MWh annually. Proposed at $15B, but not economic. Chansey Islands:20 miles off Saint Malo, France; 34 billion kWh per year; not economic; environmental problems; project shelved in 1980 San Jose, Argentina: potential of 75 billion kWh/year; tidal range of 20 feet (6m) China built several plants in the 1950s Korean potential sites (Garolim Bay) 040323

15.4 Wave Energy Energy of interchanging potential and kinetic energy in the wave Cycloidal motion of wave particles carries energy forward without much current Typical periodicities are one to thirty seconds, thus there are low-energy periods between high-energy points In 1799, Girard & Son of Paris proposed using wave power for powering pumps and saws California coast could generate 7 to 17 MW per mile [Smith, p. 91] 040324

15.4 Ocean Energy: Wave Energy Wave energy potential varies greatly worldwide Figures in kW/m Source: Wave Energy paper. IMechE, 1991 and European Directory of Renewable Energy (Suppliers and Services) 1991 040323

15.4.1 Concepts of Wave Energy Conversion Change of water level by tide or wave can move or raise a float, producing linear motion from sinusoidal motion Water current can turn a turbine to yield rotational mechanical energy to drive a pump or generator Slow rotation speed of approximately one revolution per second to one revolution per minute less likely to harm marine life Turbine reduces energy downstream and could protect shoreline Archimedes Wave Swing is a Dutch device [Smith, p. 91] 040323

15.4.2 Water Current Equations (also applies to wind turbines) Assume a “tube” of water the diameter, D, of the rotor A = π D2/4 A length, L, of water moves through the turbine in t seconds L = u·t, where u is the water speed The tube volume is V = A·L = A·u·t Water density, ρ, is 1000 kg/m3 Mass, m = ρ·V = ρ·A·u·t, where V is volume Kinetic energy = KE = ½ mu2 040323

15.4.2 Water Current Equations (continued) Substituting ρ·A·u·t for mass, and A = π D2/4 , KE = ½·π/4·ρ·D2·u3·t Theoretical power, Pt = ½·π/4·ρ·D2·u3·t/t = 0.3927·ρW·D2·u3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axis Betz Law shows 59.3% of power can be extracted Pe = Pt·59.3%·r·t·g, where Pe is the extracted power, r is rotor efficiency, t is transmission efficiency, and g is generator efficiency For example, 59.3%·90%·98%·80% = 42% extraction of theoretical power 040324

15.4.3 Salter “Ducks” Scottish physicist Prof. Stephen Salter invented “Nodding Duck” energy converter in 1970 Salter “ducks” rock up and down as the wave passes beneath it. This oscillating mechanical energy is converted to electrical energy Destroyed by storm A floating two-tank version drives hydraulic rams that send pressurized oil to a hydraulic motor that drives a generator, and a cable conducts electricity to shore Ref.: www.fujita.com/archive-frr/ TidalPower.html ©1996 Ramage http://acre.murdoch.edu.au/ago/ocean/wave.html 040323

15.4.4.1 Water-Driven Wave Turbines Davis Hydraulic Turbines since 1981 Most tests done in Canada 4 kW turbine tested in Gulf Stream Blue Energy of Canada developing two 250 kW turbines for British Columbia Also proposed Brothers Island tidal fence in San Francisco Bay, California 1000 ft long by 80 ft deep to produce 15 – 25 MW Australian Port Kembla (south of Sydney) to produce 500 kW 040323

15.4.4.1 Water-Driven Wave Turbines Waves can be funneled and channeled into a rising chute to charge a reservoir over a weir or through a swing-gate Water passes through waterwheel or turbine back to the ocean Algerian V-channel [Kotch, p.228] Wave forces require an extremely strong structure and mechanism to preclude damage The Ocean Power Delivery wave energy converter Pelamis has articulated sections that stream from an anchor towards the shore Waves passing overhead produce hydraulic pressure in rams between sections This pressure drives hydraulic motors that spin generators, and power is conducted to shore by cable 750 kW produced by a group 150m long and 3.5m diameter 040323

15.4.4.2 Air-Driven Wave Turbines A Wavegen™, wave-driven, air compressor or oscillating water column (OWC) spins a two-way Wells turbine to produce electricity This British invention uses an air-driven Wells turbine with symmetrical blades Incoming waves pressurize air within a heavy concrete box, and trapped air rushes upward through pipe connecting the turbine Wells turbine is spun to starting speed by external electrical power and spins the same rotation regardless of air flow direction Energy is estimated at 65 megawatts per mile Photo by Wavegen http://www.bfi.org/Trimtab/summer01/oceanWave.htm 040324

15.4.4.2 Air-Driven Wave Turbines (Con’t) A floating buoy can compress trapped air similar to a whistle buoy The oscillating water column (OWC) in a long pipe under the buoy will lag behind the buoy motion due to inertia of the water column The compressed air spins a turbine/alternator to generate electricity at $0.09/kWh The Japanese “Mighty Whale” has an air channel to capture wave energy. Width is 30m and length is 50 m. There are two 30 kW and one 50 kW turbine/generators http://www.earthsci.org/esa/energy/wavpwr/wavepwr.html 040324

15.5 Ocean Energy: OTEC (Ocean Thermal Electric Conversion) Hawaii has the research OTEC system [shut down in 1985?] OTEC requires some 40°F temperature difference between the surface and deep waters to extract energy Open-cycle plants vaporize warm water and condense it using the cold sea water, yielding potable water and electricity from turbine-driven alternators Closed-cycle units evaporate ammonia at 78°F to drive a turbine and an alternator Ref.: www.nrel.gov/otec/achievements.html 040324

15.6 Current Flow Turbines Current flow turbines are essentially waterproof underwater wind turbines The forces are much greater since water has 832 times the density of air Turbines can turn slowly and are less likely to damage marine animals This version is raised above the water surface for maintenance 040324

15.7 Hydraulic Pressure Absorbers for Wave and Tide Large synthetic rubber bags filled with water could be placed offshore where large waves pass overhead Also respond to tides A connecting pipe conducts hydraulic pressure to a positive displacement motor that spins a generator The motor can turn a generator to make electricity that varies sinusoidally with the pressure http://www.bfi.org/Trimtab/summer01/oceanWave.htm 040323

15.8 Other Issues Biofouling can clog intake pipes or other parts of submerged equipment Storms can tear loose moorings, leading to loss of equipment Offshore units may pose a navigation hazard Simple obstruction Adrift from a storm NIMBYs may not want to see them and loudly protest 040324

15.C Conclusion Renewable energy offers a long-term approach to the World’s energy needs Economics drives the energy selection process and short-term (first cost) thinking leads to disregard of long-term, overall cost Wave and tidal energy are more expensive than wind and solar energy, the present leaders Increasing oil, gas, and coal prices will ensure that the transition to renewable energy occurs Offshore and shoreline wind energy plants offer a logical approach to part of future energy supplies 040324

References: Books, etc. General: Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0-12-656152-4. Henry, J. Glenn and Gary W. Heinke. Environmental Science and Engineering. Englewood Cliffs: Prentice-Hall, 728pp., 1989. 0-13-283177-5, TD146.H45, 620.8-dc19 Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0-262-02349-0, TJ807.9.U6B76, 333.79’4’0973. Di Lavore, Philip. Energy: Insights from Physics. NY: John Wiley & Sons, 414pp., 1984. 0-471-89683-7l, TJ163.2.D54, 621.042. Bowditch, Nathaniel. American Practical Navigator. Washington:USGPO, H.O. Pub. No. 9. Harder, Edwin L. Fundamentals of Energy Production. NY: John Wiley & Sons, 368pp., 1982. 0-471-08356-9, TJ163.9.H37, 333.79. Tidal Energy, pp. 111-129. Wind: Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136 Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5 Johnson, Gary L, Wind Energy Systems. Englewood Cliffs NJ: Prentice-Hall, Inc. TK 1541.J64 1985. 621.4’5; 0-13-957754-8. Waves: Smith, Douglas J. “Big Plans for Ocean Power Hinges on Funding and Additional R&D”. Power Engineering, Nov. 2001, p. 91. Kotch, William J., Rear Admiral, USN, Retired. Weather for the Mariner. Annapolis: Naval Institute Press, 1983. 551.5, QC994.K64, Chap. 11, Wind, Waves, and Swell. Solar: Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991. 040323

References: Books Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0-262-02349-0, TJ807.9.U6B76, 333.79’4’0973. Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991 Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5 Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136 Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0-12-656152-4. 040323

References: Internet General: Tidal: Waves: http://www.google.com/search?q=%22renewable+energy+course%22 http://www.ferc.gov/ Federal Energy Regulatory Commission http://solstice.crest.org/ http://dataweb.usbr.gov/html/powerplant_selection.html http://mailto:energyresources@egroups.com http://www.dieoff.org. Site devoted to the decline of energy and effects upon population Tidal: http://www.unep.or.kr/energy/ocean/oc_intro.htm http://www.bluenergy.com/technology/prototypes.html http://www.iclei.org/efacts/tidal.htm http://zebu.uoregon.edu/1996/ph162/l17b.html http://www.bluenergy.com/public/index_2.html Waves: http://www.env.qld.gov.au/sustainable_energy/publicat/ocean.htm http://www.bfi.org/Trimtab/summer01/oceanWave.htm http://www.oceanpd.com/ http://www.newenergy.org.cn/english/ocean/overview/status.htm http://www.energy.org.uk/EFWave.htm http://www.earthsci.org/esa/energy/wavpwr/wavepwr.html 040324

References: Internet Thermal: Wind: http://www.nrel.gov/otec/what.html http://www.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systems Wind: http://awea-windnet@yahoogroups.com. Wind Energy elist http://awea-wind-home@yahoogroups.com. Wind energy home powersite elist http://telosnet.com/wind/20th.html 040323

References: Websites, etc. awea-windnet@yahoogroups.com. Wind Energy elist awea-wind-home@yahoogroups.com. Wind energy home powersite elist geothermal.marin.org/ on geothermal energy mailto:energyresources@egroups.com rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy map of CONUS windenergyexperimenter@yahoogroups.com. Elist for wind energy experimenters www.dieoff.org. Site devoted to the decline of energy and effects upon population www.ferc.gov/ Federal Energy Regulatory Commission www.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systems telosnet.com/wind/20th.html www.google.com/search?q=%22renewable+energy+course%22 solstice.crest.org/ dataweb.usbr.gov/html/powerplant_selection.html 040325

Units and Constants Units: Power in watts (joules/second) Energy (power x time) in watt-hours Constants: 1 m = 0.3048 ft exactly by definition 1 mile = 1.609 km; 1m/s = 2.204 mi/h (mph) 1 mile2 = 27878400 ft2 = 2589988.11 m2 1 ft2 = 0.09290304 m2; 1 m2 = 10.76391042 ft2 1 ft3 = 28.32 L = 7.34 gallon = 0.02832 m3; 1 m3 = 264.17 US gallons 1 m3/s = 15850.32 US gallons/minute g = 32.2 ft/s2 = 9.81 m/s2; 1 kg = 2.2 pounds Air density, ρ (rho), is 1.225 kg/m3 or 0.0158 pounds/ft3 at 20ºC at sea level Solar Constant: 1368 W/m2 exoatmospheric or 342 W/m2 surface (80 to 240 W/m2) 1 HP = 550 ft-lbs/s = 42.42 BTU/min = = 746 W (J/s) 1 BTU = 252 cal = 0.293 Wh = 1.055 kJ 1 atmosphere = 14.696 psi = 33.9 ft water = 101.325 kPa = 76 cm Hg =1013.25 mbar 1 boe (42- gallon barrel of oil equivalent) = 1700 kWh 040323

Energy Equations Electricity: Turbines: E=IR; P=I2 R; P=E2/R, where R is resistance in ohms, E is volts, I is current in amperes, and P is power in watts Energy = P t, where t is time in hours Turbines: Pa = ½ ρ A2 u3, where ρ (rho) is the fluid density, A = rotor area in m2, and u is wind speed in m/s P = R ρ T, where P = pressure (Nm-2 = Pascal) Torque, T = P/ω, in Nm/rad, where P = mechanical power in watts, ω is angular velocity in rad/sec Pumps: Pm = gQmh/ήp W, where g=9.81 N/kg, Qm is mass capacity in kg/s, h is head in m, and ήp is pump mechanical efficiency 040323