15 0 Ocean Energy It is pleasant when

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

15. 1 Ocean Energy l 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 l The tidal gravitational forces and thermal storage of the ocean provide a major energy source l Wave action adds to the extractable surface energy, but is less than tidal energy l Major ocean currents (like the Gulf Stream) may be exploited to extract energy with underwater rotors similar to wind turbines 040324

15. 1 History l Some first uses of ocean energy: u. Tidal grain mills developed u. Currents used to cross the Atlantic and return u. Ocean winds blow boats (sometimes where desired) 040324

15. 2 Sources of Energy l Tidal motion of water up and down changes potential energy u. Changes of pressure beneath the tide height u. Tidal horizontal flow into basins and rivers results l Wind-driven motion of water horizontally increases kinetic energy u. Changes in flow rate that produces strong currents l Solar heating of surface waters warms the ocean by conduction u. Upwelling and overturning mixes and heats lower layers 040325

15. 2. 1 Available Energy l Potential Energy: PE = mh l Kinetic Energy: KE = ½ mv 2 or ½ mu 2 l Wave energy is proportional to wave length times wave height squared (LH 2)per wave length per unit of crest length u 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] l Maximum Tidal Energy, E = 2 HQ x 353/(778 x 3413) = 266 x 10 -6 HQ k. Wh/yr, where H is the tidal range (ft) and Q is the tidal flow (lbs of seawater) l E = 2 HQ ft-lb/lunar day (2 tides) or E = 416 x 10 -4 HV k. Wh, where V is cubic feet of flow 040323

15. 3 Ocean Energy: Tidal Energy l Tides are produced by gravitational forces of the moon and sun and the Earth’s rotation l Existing and possible sites: u. France: 1966 La Rance river estuary 240 MW station n Tidal ranges of 8. 5 m to 13. 5 m; 10 reversible turbines u. England: Severn River u. Canada: Passamaquoddy in the Bay of Fundy (1935 attempt failed) u. California: high potential along the northern coast l Environmental, economic, and esthetic aspects have delayed implementation l Lunar/solar power is asynchronous with daily load cycle 040325

15. 3 Tidal Energy l Tidal mills were used in the Tenth and Eleventh Centuries in England, France, and elsewhere l Millpond water was trapped at high tide by a gate (Difficult working hours for the miller; Why? ) u Rhode Island, USA, 18 th Century, 20 -ton wheel 11 ft in diameter and 26 ft wide u Hamburg, Germany, 1880 “mill” pumped sewage u Slade’s Mill in Chelsea, MA founded 1734, 100 HP, operated until ~1980 u 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!) u Tidal mills were common in USA north of Cape Cod, where a 3 m range exists [Redfield, 1980] u Brooklyn NY had tidal mill in 1636 [? ] 040323

15. 3 Tidal Energy (continued) l Potential energy = S integral from 0 to 2 H (ρgz dz), where S is basin area, H is tidal amplitude, ρ is water density, and g is gravitational constant yielding 2 S ρ g. H 2 l Mean power is 2 S ρ g. H 2/tidal period; semidiurnal better l Tidal Pool Arrangements u Single-pool empties on ebb tide u Single-pool fills on flood tide u Single-pool fills and empties through turbine u Two-pool ebb- and flood-tide system; two ebbs per day; alternating pool use u Two-pool one-way system (high and low pools) (turbine located between pools) 040323

15. 3. 1 Tidal Water Turbines l Current flow converted to rotary motion by tidal current l Turbines placed across Rance River, France l Large Savonius rotors (J. S. Savonius, 1932? ) placed across channel to rotate at slow speed but creating high torque (large current meter) l Horizontal rotors proposed for Gulf Stream placement off Miami, Florida 040323

15. 3. 1. 1 Tidal Flow: Rance River, France l l l 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 k. Wh/year; 6% extracted l Storage pumping contributes 1. 7% to energy level l At neap tides, generates 80, 000 k. Wh/day; at equinoctial spring tide, 1, 450, 000 k. Wh/day (18: 1 ratio!); average ~500 million k. Wh/year l 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 l l l l 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 l Deferred until economic conditions change [Ref. : Harder] 040323

15. 3. 1. 3 Other Tidal Flow Plants under Study l 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. ; ~$74 M l Experimental site at Kislaya Guba on Barents Sea u French 400 k. W unit operated since 1968 u Plant floated into place and sunk: dikes added to close gaps l Sea of Okhotsk (former Sov. Union) under study in 1980 l White Sea, Russia: 1 MW, 1969 l Murmansk, Russia: 0. 4 MW l Kiansghsia in China 040324

15. 3. 1. 3 Other Tidal Flow Plants under Study (continued) l Severn River, Great Britain: range of 47 feet (14. 5 m) calculated output of 2. 4 MWh annually. Proposed at $15 B, but not economic. l Chansey Islands: 20 miles off Saint Malo, France; 34 billion k. Wh per year; not economic; environmental problems; project shelved in 1980 l San Jose, Argentina: potential of 75 billion k. Wh/year; tidal range of 20 feet (6 m) l China built several plants in the 1950 s l Korean potential sites (Garolim Bay) 040323

15. 4 Wave Energy l Energy of interchanging potential and kinetic energy in the wave l Cycloidal motion of wave particles carries energy forward without much current l Typical periodicities are one to thirty seconds, thus there are low-energy periods between high-energy points l In 1799, Girard & Son of Paris proposed using wave power for powering pumps and saws l California coast could generate 7 to 17 MW per mile [Smith, p. 91] 040324

15. 4 Ocean Energy: Wave Energy l Wave energy potential varies greatly worldwide Figures in k. W/m Source: Wave Energy paper. IMech. E, 1991 and European Directory of Renewable Energy (Suppliers and Services) 1991 040323

15. 4. 1 Concepts of Wave Energy Conversion l Change of water level by tide or wave can move or raise a float, producing linear motion from sinusoidal motion l Water current can turn a turbine to yield rotational mechanical energy to drive a pump or generator u Slow rotation speed of approximately one revolution per second to one revolution per minute less likely to harm marine life u Turbine reduces energy downstream and could protect shoreline l Archimedes Wave Swing is a Dutch device [Smith, p. 91] 040323

15. 4. 2 Water Current Equations (also applies to wind turbines) l Assume a “tube” of water the diameter, D, of the rotor u. A = π D 2/4 l A length, L, of water moves through the turbine in t seconds u. L = u·t, where u is the water speed l The tube volume is V = A·L = A·u·t l Water density, ρ, is 1000 kg/m 3 l Mass, m = ρ·V = ρ·A·u·t, where V is volume l Kinetic energy = KE = ½ mu 2 040323

15. 4. 2 Water Current Equations (continued) l Substituting ρ·A·u·t for mass, and A = π D 2/4 , KE = ½·π/4·ρ·D 2·u 3·t l Theoretical power, Pt = ½·π/4·ρ·D 2·u 3·t/t = 0. 3927·ρW·D 2·u 3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axis l Betz Law shows 59. 3% of power can be extracted l 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 l For example, 59. 3%· 90%· 98%· 80% = 42% extraction of theoretical power 040324

15. 4. 3 Salter “Ducks” l Scottish physicist Prof. Stephen Salter invented “Nodding Duck” energy converter in 1970 l Salter “ducks” rock up and down as the wave passes beneath it. This oscillating mechanical energy is converted to electrical energy l Destroyed by storm l 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 http: //acre. murdoch. edu. au/ago/ocean/wave. html 040323 Ref. : www. fujita. com/archive-frr/ Tidal. Power. html © 1996 Ramage

15. 4. 4. 1 Water-Driven Wave Turbines l Davis Hydraulic Turbines since 1981 u. Most tests done in Canada u 4 k. W turbine tested in Gulf Stream l Blue Energy of Canada developing two 250 k. W turbines for British Columbia l Also proposed Brothers Island tidal fence in San Francisco Bay, California 1000 ft long by 80 ft deep to produce 15 – 25 MW l Australian Port Kembla (south of Sydney) to produce 500 k. W 040323

15. 4. 4. 1 Water-Driven Wave Turbines l Waves can be funneled and channeled into a rising chute to charge a reservoir over a weir or through a swing-gate u Water passes through waterwheel or turbine back to the ocean u Algerian V-channel [Kotch, p. 228] l Wave forces require an extremely strong structure and mechanism to preclude damage l The Ocean Power Delivery wave energy converter Pelamis has articulated sections that stream from an anchor towards the shore u Waves passing overhead produce hydraulic pressure in rams between sections u This pressure drives hydraulic motors that spin generators, and power is conducted to shore by cable u 750 k. W produced by a group 150 m long and 3. 5 m diameter 040323

15. 4. 4. 2 Air-Driven Wave Turbines l A Wavegen™, wave-driven, air compressor or oscillating water column (OWC) spins a two-way Wells turbine to produce electricity l This British invention uses an air-driven Wells turbine with symmetrical blades l Incoming waves pressurize air within a heavy concrete box, and trapped air rushes upward through pipe connecting the turbine l Wells turbine is spun to starting speed by external electrical power and spins the same rotation regardless of air flow direction l Energy is estimated at 65 megawatts per mile Photo by Wavegen http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm 040324

15. 4. 4. 2 Air-Driven Wave Turbines (Con’t) l A floating buoy can compress trapped air similar to a whistle buoy l 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 l The compressed air spins a turbine/alternator to generate electricity at $0. 09/k. Wh The Japanese “Mighty Whale” has an air channel to capture wave energy. Width is 30 m and length is 50 m. There are two 30 k. W and one 50 k. W turbine/generators http: //www. earthsci. org/esa/energy/wavpwr/wavepwr. html 040324

15. 5 Ocean Energy: OTEC (Ocean Thermal Electric Conversion) l Hawaii has the research OTEC system [shut down in 1985? ] l OTEC requires some 40°F temperature difference between the surface and deep waters to extract energy l Open-cycle plants vaporize warm water and condense it using the cold sea water, yielding potable water and electricity from turbine-driven alternators l 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 l Current flow turbines are essentially waterproof underwater wind turbines l The forces are much greater since water has 832 times the density of air l Turbines can turn slowly and are less likely to damage marine animals l This version is raised above the water surface for maintenance 040324

15. 7 Hydraulic Pressure Absorbers for Wave and Tide l Large synthetic rubber bags filled with water could be placed offshore where large waves pass overhead u. Also respond to tides u. A connecting pipe conducts hydraulic pressure to a positive displacement motor that spins a generator u. The motor can turn a generator to make electricity that varies sinusoidally with the pressure http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm 040323

15. 8 Other Issues l Biofouling can clog intake pipes or other parts of submerged equipment l Storms can tear loose moorings, leading to loss of equipment l Offshore units may pose a navigation hazard u. Simple obstruction u. Adrift from a storm l NIMBYs may not want to see them and loudly protest 040324

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

References: Books, etc. l l l 040323 General: u Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0 -12656152 -4. u Henry, J. Glenn and Gary W. Heinke. Environmental Science and Engineering. Englewood Cliffs: Prentice. Hall, 728 pp. , 1989. 0 -13 -283177 -5, TD 146. H 45, 620. 8 -dc 19 u Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0 -262 -02349 -0, TJ 807. 9. U 6 B 76, 333. 79’ 4’ 0973. u Di Lavore, Philip. Energy: Insights from Physics. NY: John Wiley & Sons, 414 pp. , 1984. 0 -471 -89683 -7 l, TJ 163. 2. D 54, 621. 042. u Bowditch, Nathaniel. American Practical Navigator. Washington: USGPO, H. O. Pub. No. 9. u Harder, Edwin L. Fundamentals of Energy Production. NY: John Wiley & Sons, 368 pp. , 1982. 0 -471 -083569, TJ 163. 9. H 37, 333. 79. Tidal Energy, pp. 111 -129. Wind: u Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0 -8493 -1605 -7, TK 1541. P 38 1999, 621. 31’ 2136 u Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co. , 1993. 0930031 -64 -4, TJ 820. G 57, 621. 4’ 5 u Johnson, Gary L, Wind Energy Systems. Englewood Cliffs NJ: Prentice-Hall, Inc. TK 1541. J 64 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, QC 994. K 64, Chap. 11, Wind, Waves, and Swell. Solar: u Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc. , 920 pp. , 1991.

References: Books l Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0 -262 -02349 -0, TJ 807. 9. U 6 B 76, 333. 79’ 4’ 0973. l Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc. , 920 pp. , 1991 l Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co. , 1993. 0 -930031 -64 -4, TJ 820. G 57, 621. 4’ 5 l Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0 -8493 -1605 -7, TK 1541. P 38 1999, 621. 31’ 2136 l Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0 -12 -656152 -4. 040323

References: Internet l General: u u u http: //www. google. com/search? q=%22 renewable+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 l Tidal: u u u 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/ph 162/l 17 b. html http: //www. bluenergy. com/public/index_2. html l Waves: u http: //www. env. qld. gov. au/sustainable_energy/publicat/ocean. htm u http: //www. bfi. org/Trimtab/summer 01/ocean. Wave. htm u http: //www. oceanpd. com/ u u http: //www. newenergy. org. cn/english/ocean/overview/status. htm http: //www. energy. org. uk/EFWave. htm u http: //www. earthsci. org/esa/energy/wavpwr/wavepwr. html 040324

References: Internet l Thermal: u http: //www. nrel. gov/otec/what. html u http: //www. hawaii. gov/dbedt/ert/otec_hi. html#anchor 349152 on OTEC systems l Wind: u http: //awea-windnet@yahoogroups. com. Wind Energy elist u http: //awea-wind-home@yahoogroups. com. Wind energy home powersite elist u http: //telosnet. com/wind/20 th. 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/chap 2/2 -01 m. 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#anchor 349152 on OTEC systems telosnet. com/wind/20 th. html www. google. com/search? q=%22 renewable+energy+course%22 solstice. crest. org/ dataweb. usbr. gov/html/powerplant_selection. html 040325

Units and Constants l Units: u Power in watts (joules/second) u Energy (power x time) in watt-hours l Constants: u 1 m = 0. 3048 ft exactly by definition u 1 mile = 1. 609 km; 1 m/s = 2. 204 mi/h (mph) u 1 mile 2 = 27878400 ft 2 = 2589988. 11 m 2 u 1 ft 2 = 0. 09290304 m 2; 1 m 2 = 10. 76391042 ft 2 u 1 ft 3 = 28. 32 L = 7. 34 gallon = 0. 02832 m 3; 1 m 3 = 264. 17 US gallons u 1 m 3/s = 15850. 32 US gallons/minute u g = 32. 2 ft/s 2 = 9. 81 m/s 2; 1 kg = 2. 2 pounds u Air density, ρ (rho), is 1. 225 kg/m 3 or 0. 0158 pounds/ft 3 at 20ºC at sea level u Solar Constant: 1368 W/m 2 exoatmospheric or 342 W/m 2 surface (80 to 240 W/m 2) u 1 HP = 550 ft-lbs/s = 42. 42 BTU/min = = 746 W (J/s) u 1 BTU = 252 cal = 0. 293 Wh = 1. 055 k. J u 1 atmosphere = 14. 696 psi = 33. 9 ft water = 101. 325 k. Pa = 76 cm Hg =1013. 25 mbar u 1 boe (42 - gallon barrel of oil equivalent) = 1700 k. Wh 040323

Energy Equations l Electricity: u E=IR; P=I 2 R; P=E 2/R, where R is resistance in ohms, E is volts, I is current in amperes, and P is power in watts u Energy = P t, where t is time in hours l Turbines: u Pa = ½ ρ A 2 u 3, where ρ (rho) is the fluid density, A = rotor area in m 2, and u is wind speed in m/s u P = R ρ T, where P = pressure (Nm-2 = Pascal) u Torque, T = P/ω, in Nm/rad, where P = mechanical power in watts, ω is angular velocity in rad/sec l Pumps: u Pm = g. Qmh/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